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金沢大学理工研究域物質化学系, Type III Cu ligand, His456 and His458, of Myrothecium verrucaria (MT-1) bilirubin oxidases (BO) [EC 1.3.3.5] were doubly mutated as to Lys, Asp, and Val. In spite of perturbation of the type III Cu centers, these mutants were pale blue or colourless when isolated. However, they became intense blue on reaction with reducing agents such as dithionite, ascorbate, hexacyanoferrate(II), and octacyanotangstate(IV) under air, or with an oxidizing agent such as hexacyanoferrate(III), indicating that they are in mixed forms when expressed in Aspergillus oryzae. His456.458Lys and His456.458Asp mutated as to potential coordinating groups showed weak BO and ferroxidase activities, while His 456.458Val mutated as to non-coordinating groups showed no enzyme activity at all.

We previously showed that bovine apolipoprotein A-II (apoA-II) has antimicrobial activity against Escherichia coli in PBS, and its C-terminal residues 49-76 are responsible for the activity using synthetic peptides. In order to understand the structural requirements of peptide 49-76 for the antimicrobial activity, the N- or C-terminus was truncated and then the charged (Lys or Asp) or Ser residues were replaced by Ala. Deletion of the first or last three amino acids and replacement of Lys-54/55 or 71/72 by Ala caused a substantial decreases in alpha-helical content in 50% TFE, showing the possible presence of helices in N- and C-terminal regions, respectively. The anti-Escherichia coli activity of the peptide correlated with its liposome-binding activity. Replacement of Lys-54/55 or 71/72 by Ala resulted in an almost complete loss of anti-E. coli activity with a substantial decrease in liposome-binding activity. Moreover, deletion of the last three amino acids caused a reduction to 1/17 of the original anti-E. coli activity with a moderate decrease in liposome-binding activity. In contrast, replacement of Ser-65/66, Asp-59, or Asp-69 by Ala hardly affected the anti-E. coli activity. These findings suggest that Lys-54/55 and Lys-71/72 on the putative helices are critical for antimicrobial activity, and the C-terminal 3 amino acids are important for the structural integrity of the C-terminal region for effective antimicrobial activity.

We have developed a new ultraviolet spectrophotometric method for measurement of serum gamma-glutamyltransferase activity. The principle of the method is as follows. Using L-gamma-glutamyl-3-chloro-4-aminobenzoate as the donor substrate, 3-chloro-4-aminobenzoate formed upon transfer of the gamma-glutamyl moiety from the donor substrate to the acceptor substrate glycylglycine is stoichiometrically converted to 3-chloro-4-hydroxyaniline by 4-aminobenzoate hydroxylase from Agaricus bisporus, coupled with the oxidation of NADH to NAD+, and the resulting decrease in absorbance at 340 nm is monitored. The results obtained indicate that there is a good possibility to establish an ultraviolet spectrophotometric method for measurement of serum gamma-glutamyltransferase activity using L-gamma-glutamyl-3-chloro-4-aminobenzoate as the donor substrate and 4-aminobenzoate hydroxylase from Agaricus bisporus as a coupling enzyme.

We previously showed that bovine apolipoprotein A-II (apoA-II) had antimicrobial activity against Escherichia coli and the yeast Saccharomyces cerevisiae in PBS. We have characterized here the active domain of apoA-II using synthetic peptides. A peptide corresponding to C-terminal residues Leu(49)-Thr(76) exhibited significant antimicrobial activity against E. coli in PBS, but not against S. cerevisiae. Experiments using amino-acid-substituted peptides indicated that the residues Phe(52)-Phe(53)-Lys(54)-Lys(55) are required for the activity. Peptide Leu(49)-Thr(76) induced the release of calcein trapped inside the vesicles whose lipid composition resembles that of E. coli membrane, suggesting that peptide Leu(49)-Thr(76) can destabilize the E. coli membrane. CD measurements showed that the alpha-helicity of peptide Leu(49)-Thr(76) increased from 3.5 to 36% by addition of the vesicles. When E. coli cells were incubated with peptide Leu(49)-Thr(76), some proteins were released to the external medium, probably owing to membrane destabilization caused by the peptide. In electron micrographs of E. coli cells treated with peptide Leu(49)-Thr(76), transparent nucleoids and granulated cytoplasm were observed. Amino acid substitutions, Phe(52)Phe(53)-->AlaAla (Phe(52, 53)-->Ala) in peptide Leu(49)-Thr(76) caused the loss of antimicrobial activity against E. coli, although protein-releasing activity was retained. Electron micrographs of the cells treated with peptide Leu(49)-Thr(76)(Phe(52,53)-->Ala) revealed morphological change only at the nucleoids. Therefore peptide Leu(49)-Thr(76) appears to primarily target the cytoplasm rather than the membrane of E. coli cells.

The regions contributing to the thermostability of inorganic pyrophosphatase (PPase, EC 3.6.1.1) from Thermus thermophilus (Tth) were deduced in our previous study by random chimeragenesis, one of them being estimated to be Ala144-Lys145 [Satoh, T., Takahashi, Y., Oshida, N., Shimizu, A., Shinoda, H., Watanabe, M., and Samejima, T. (1999) Biochemistry 38, 1531-1536]. Therefore, we investigated the contributions of these two residues in Tth by preparing a deletion mutant (del.144-145 mutant) of Tth PPase. We examined its thermostability in terms of the CD and fluorescence spectra, and the thermal change in the enzymatic activity. The thermostability of the enzymatic activity of the del.144-145 mutant was similar to that of the wild type Tth PPase, whereas this mutant was more stable against heating. Furthermore, we compared the thermal aggregation of the wild type with that of the del.144-145 mutant. We found that the thermal aggregation of the mutant was reduced relative to that of the wild type. Moreover, the molecular weight of the mutant after heating at 90 degrees C was higher than that of the unheated one, whereas the wild type aggregated under the same conditions. Therefore, we can conclude that although the Ala144-Lys145 residues in Tth PPase may partly cause thermal aggregation, the deletion of these residues may stabilize the Tth PPase molecule structurally against heating and suppress thermal aggregation.

Baker's asthma, a typical occupational allergic disease, is a serious problem in the food industries. In this study, purification and identification of major allergens recognized by IgEs in sera of allergic patients were performed. Major immunoreactive proteins were purified from the albumin fraction by gel filtration on a Toyopearl HW-50 column followed by reverse-phase HPLC. The N-terminal amino acid sequences and molecular masses measured by MS indicated that the major immunoreactive proteins are members of the α-amylase inhibitor family, 0.19 and 0.28. Significant leukotriene release by each purified protein was observed in cell-associated stimulation tests, suggesting in vivo activity of these antigens. Carbohydrate analyses of major allergens indicated that they are monoglycosylated but not N-glycosylated in spite of the presence of a potential N-glycosylation site. Recombinant 0.19 expressed in Escherichia coli showed the same reactivity with IgE as native wheat 0.19 in Western blotting and ELISA using methyl vinyl ether maleic anhydride co-polymer as an immobilizing reagent, suggesting that the allergenic epitopes are located in the peptide portions.

Previous reports on the chaperone activity of alpha-crystallin to prevent protein denaturation and thermal aggregation have suggested that partially denatured proteins can bind alpha-crystallin in its central region. Likewise, beta- and gamma-crystallin can also be localized to the central cavity of alpha-crystallin particle in vivo, which provides indirect evidence that alpha-crystallin can function as a chaperone in the intact lens. In this study, we have further demonstrated that the binding of the substrate proteins to alpha-crystallin by short-term preincubation may mimic the in vivo conditions of crystallin association. Preheating of alpha-crystallin with its substrate proteins at 60 degrees C for 20 min resulted in the formation of stable complexes between alpha-crystallin and its substrates (8.0% of insulin or 5.3% of gamma-crystallin was involved in complex formation). Under such conditions, the chaperone activity of alpha-crystallin to inhibit dithiothreitol-, ultraviolet-, or oxidation-induced protein aggregation can be greatly enhanced. Since UV-irradiation and oxidative stress are common insults to eye lenses under normal physiological conditions, the presence of alpha/gamma and alpha/beta complex in vivo may play an important role to maintain the lens in a transparent state.

A synthetic gene encoding 0.19 alpha-amylase inhibitor (alpha-AI) from wheat kernel was obtained by enzymatic assembly of 18 oligodeoxynucleotides which were chemically synthesized. The synthetic gene was introduced into vector pET15b for expression in Escherichia coli BL21(DE3) under the control of T7 promoter. However, in SDS-PAGE and Western blotting analyses of the E. coli cell lysate, the expression product could not be detected. Expression analysis for various partially deleted gene fragments suggested that the putative hairpin-like structure of mRNA in the 5'-terminal coding region might interrupt efficient expression. When the hairpin structure was eliminated by using degenerate codons, the resulting gene could be overexpressed in E. coli. Although the gene product was accumulated in an insoluble fraction as inclusion bodies, its inhibitory activity could be recovered by solubilization with 8 M urea, followed by refolding through two successive steps of dialysis at alkaline pH. After purification, the recombinant 0.19 alpha-AI showed the same characteristics as the authentic inhibitor in terms of N-terminal amino acid sequence, peptide mapping on reverse-phase HPLC, far-UV circular dichroism (CD) spectrum and have inhibition of human salivary alpha-amylase. Thus, we have established an overexpression system in E. coli for active recombinant 0.19 alpha-AI.

alpha-Crystallin, a major protein of the lens, is known to have chaperone activity to protect other proteins against thermal aggregation. Heat-induced structural change of alpha-crystallin was previously shown to increase its chaperone activity. In this report, we studied the thermal reversibility of alpha-crystallin and the effect of change in secondary structure on its chaperone function in vitro. The heat-induced conformational changes in the aromatic region of near-UV CD spectra showed only a small degree of reversibility. The structural transitions from 50 to 70 degrees C were largely reversible if the incubation time was short. However, the protective ability to inhibit thermal aggregation of alcohol dehydrogenase by alpha-crystallin was essentially similar at 48 and 70 degrees C. Under long-term heating at high temperatures, there was a time-dependent irreversibility of structural change in alpha-crystallin as revealed by CD spectroscopy. Such denatured alpha-crystallin by long-term heating can still preserve its ability to prevent UV-induced aggregation of gamma-crystallin at room temperature, indicating relatively little effect of heat-induced changes in secondary structure on the chaperone activity of alpha-crystallin.

A series of NH2-terminal truncated forms of human cysteine proteinase inhibitor, cystatin A, was prepared by genetic engineering using Escherichia coli harboring mutated genes. Each variant of cystatin A was efficiently expressed as a fused protein with porcine adenylate kinase and released by CNBr degradation after exchange of the sole inner Met to Leu. The mutant cystatin A lacking an amino-terminal Met residue (called standard variant starting from Ile2, CystA2-98(M65L) showed the same inhibitory activity as authentic one isolated from human epidermis. Two-residue truncation scarcely influenced the activity, but further truncations deleting Pro3 and beyond conservative Gly4 and Gly5 caused a remarkable decrease of their inhibitory activity. But little effect was observed by a substitution of Pro3 with Leu. The loss of the activity by amino-terminal truncation was compensated slightly by engineered substitution of Gly75 with His on a second loop. In the two-dimensional 15N-1H HSQC NMR spectrum, four-residue truncation was found to cause changes in the chemical shifts of Val47 and Val48, which locate on a first loop and consist of a conservative QVVAG sequence. Furthermore, the truncation led to a change in fluorescence spectroscopic behavior of Trp75, which was introduced as a probe on the second loop. Fluorescence intensity of the Trp of the truncated (5-98) form was more affected by heating than the active standard variant. Conversely, fluorescence of Trp75 in 2-98 form was more quenched by acrylamide than the 5-98 variant. Thus, the amino-terminal region of cystatin A is essential for the expression of its inhibitory activity.(ABSTRACT TRUNCATED AT 250 WORDS)

The expression system for human recombinant cystatin A has already been established to be a fusion protein with porcine adenylate kinase in Escherichia coli [Kaji et al. (1990) Biol. Chem. Hoppe-Seyler 371, Suppl., 145-150]. After cyanogen bromide cleavage of the fused protein expressed in E. coli, the cystatin portion could be readily isolated. The inhibitory activity of the obtained variant (Cyst A (2-98)) was found to be almost identical with that of the wild type, and thereafter a mutation was introduced into this variant (Ctst A(2-98)), called the standard variant. To elucidate the role of the Gly-4 residue, which is completely conserved in all cystatin species, this residue was substituted with 17 other amino acids by means of cassette mutagenesis. Thus 17 variants (Cyst A(2-98)[G4X]) obtained were examined as to their inhibitory activity towards papain. As the side chain of the substituted amino acid residue became more bulky, the inhibitory activity of the variant markedly decreased. Variants whose side chains were bulkier than a Val residue showed almost no inhibitory effect towards papain. Consequently, it was deduced that the large side chain of a substituted amino acid may cause steric hindrance, which may be responsible for the decrease in inhibitory activity. Thus, we could conclude that the 4th (Gly) residue on cystatin A must be small, because amino acids which existed on the N-terminal side of this residue could interact with a papain molecule.

Myrothecium verrucaria bilirubin oxidase expressed in Aspergillus oryzae is in a resting form different from that of the authentic bilirubin oxidase, but reaches the resting form of the authentic enzyme after one cycle of reduction and reoxidation with dioxygen as shown by the absorption and electron paramagnetic resonance spectra.

Reaction of methyl 2-deoxy-2-C-(3-bromoacetoxypropyl)-α-D-arabinofuranosides, prepared from methyl 2,3-anhydro-α-D-ribofuranoside, with oligodeoxyribonucleotide (21mer) in acetonitrile-H2O (pH 7) and subsequent treatment with piperidine resulted in the cleavage of the nucleotide chain at the position G, A, and C.

The conformation of bilirubin oxidase (EC 1.3.3.5) from Myrothecium verrucaria was studied by circular dichroism (CD). The far-UV CD spectrum showed a single minimum at 215 nm and a maximum near 198 nm, suggesting the dominance of beta-sheets. There was another negative band at 187 nm that is absent from the spectra of model alpha-helix or beta-sheet. CD analysis by the method of Chang et al. agreed well with the estimates based on the Chou and Fasman sequence-predictive method, but the Provencher-Glöckner method of CD analysis agreed well with the sequence-predictive method of Garnier et al. At pH 12 the 215- and 187-nm bands completely disappeared and the protein was denatured. This denaturation was accompanied by the appearance of a large positive band at 250 nm, probably due to ionization of tyrosine residues. In 20 mM sodium dodecyl sulfate the magnitude of the 215-nm band increased, but the spectrum transformed to that of partial helices after heating at 100 degrees C. In 6 M guanidine hydrochloride the far-UV CD spectrum was monotonic and became more negative at the lower wavelength limit (near 212 nm), suggesting that the secondary structure of the protein was disrupted. However, the near-UV CD spectrum retained residual aromatic bands even after heating at 100 degrees C. Thus, our denaturation studies suggest that bilirubin oxidase has a rigid tertiary structure.

Myrothecium verrucaria bilirubin oxidase (EC 1.3.3.5) is an enzyme catalyzing the oxidation of bilirubin to biliverdin and other substrates. We have purified bilirubin oxidase from the medium of M. verrucaria and determined its partial amino acid sequence and isolated cDNA fragment amplified by polymerase chain reaction using oligonucleotide primers designed on the basis of the partial amino acid sequence. The gene for bilirubin oxidase has been cloned from a genomic library using the cDNA fragment as a probe. The gene encodes a precursor of bilirubin oxidase consisting of 572 amino acid residues, which comprises the prepro-region of 38 amino acid residues and the mature enzyme of 534 amino acid residues containing one cysteine. Five introns were found within the coding region. Sequence comparison of bilirubin oxidase with other blue copper proteins (laccase, ascorbate oxidase, human ceruloplasmin, plastocyanin, and azurin) revealed the presence of four domains corresponding to potential copper ligands. We have expressed this bilirubin oxidase gene in Saccharomyces cerevisiae under the repressible acid phosphatase promotor and found an active recombinant bilirubin oxidase, establishing the functional identity of the gene.

A rat cystatin A cDNA clone was isolated from a lambda ZAP library representing newborn rat skin mRNA by screening with a synthetic oligonucleotide designed from amino acid sequence 15-23 of the cysteine proteinase inhibitor. The obtained clone contained a partial coding region of the inhibitor, lacking the 5'-untranslated region and coding sequence for the NH(2)-terminal 13 residues. The amino acid sequence deduced from the base sequence, Glu14-Phe103, coincided with that determined at the amino acid level. To obtain the recombinant cystatin A protein, the DNA was fused with a synthetic linker encoding its missing N-terminal 17 residues and introduced into an expression vector, pMK2. In Escherichia coli, however, the expression level of the semi-synthetic gene was low, 0. 5 mg of the purified recombinant protein per 1 liter culture being produced. Changing of the codon usage of the N-terminal region in a pET-15b expression system led to an increase in the yield depending on the instability of the putative secondary structure around an initiation codon of the mRNA. The expressed cystatin A showed identical characteristics with the authentic form except for the absence of the N-terminal acetyl blocking group. Using the expression system, two kinds of point mutation, the conservative Val54 in the first loop QxVxG region being changed to Lys and Glu, were introduced, but there was almost no effect on the inhibitory activity toward papain. This suggests that the conserved Val in the reactive site is not restricted and that the hydrophobicity of the position is not essential for the activity of rat cystatin A.

4-aminobenzoate hydroxylase (4ABH) is a flavin-dependent monooxygenase that catalyzes the decarboxylative hydroxylation of 4-aminobenzoate to 4-hydroxyaniline. For use as a clinical reagent, the gene encoding 4ABH from Agaricus bisporus was cloned by the RACE method. Also, the cDNA encoding 4ABH was expressed in Escherichia coli cells as a fusion protein with glutathione S-transferase (GST). The expressed GST-4ABH fusion protein (recombinant 4ABH) in the soluble fraction exhibits decarboxylative hydroxylation and additional NADH oxidation activities.We investigated a new ultraviolet spectrometric method for determining serum gamma-glutamyltransferase (gamma-GT) using recombinant 4ABH as a coupling enzyme. The principle of the method is as follows. Using gamma-glutamyl-3-choloro-4-aminobenzoate (L-gamma-glu-PAClBA) and glycylglycine as the donor and acceptor substrates, 3-choloro-4-aminobenzoate (PAClBA) is formed by the catalysis of serum gamma-GT. PAClBA is stoichiometrically converted to 3-choloro-4-hydroxyaniline (PHClA) and NAD(+) by 4ABH and NADH. However, NADH oxidation results in a high reagent blank, which is considered as a drawback for use as a clinical reagent. Using recombinant 4ABH, we examined the effects of pH and detergents on these two activities, and found that several detergents suppress the additional NADH oxidation activity with little or no effect on hydroxylation activity. The results indicate a promising approach to establishing an ultraviolet spectrophotometric method for determining serum gamma-GT activity using L-gamma-glu-PAClBA as the donor substrate and recombinant 4ABH as a coupling enzyme.

In our previous paper, we reported a mutant of recombinant Myrothecium verrucaria bilirubin oxidase, in which the Met467 residue was replaced by Gly [Shimizu, A. et al. (1999) Biochemistry 38, 3034-3042]. This mutant displayed a remarkable reduction in enzymatic activity and an evident decrease in the intensity of the absorption band around 600 nm (type 1 charge transfer transition). In this study, we report the preparation of three Met467 mutants (Met467Gln, Met467His, and Met467Arg) and characterize their enzymatic activities, midpoint potentials, and absorption and ESR spectra. Met467His and Met467Arg show no enzymatic activity and a great reduction in the intensity of the absorption band around 600 nm. Furthermore, their ESR spectra show no type 1 copper signal, but only a type 2 copper signal; however, oxidation by ferricyanide caused the type 1 copper signal to appear. On the other hand, Met467Gln as expressed shows both type 1 and type 2 copper signals in its ESR spectrum, the type 1 copper atom parameters being very different from usual blue copper proteins but very similar to those of stellacyanin. The enzymatic activity of the Met467Gln mutant for bilirubin is quite low (0.3%), but the activity for potassium ferrocyanide is similar (130%) to that of the wild type enzyme. These results indicate that Met467 is important for characterizing the features of the type 1 copper of bilirubin oxidase.

Bilirubin oxidase (EC:1.3.3.5) purified from a culture medium of Myrothecium verrucaria MT-1 (authentic enzyme) catalyzes the oxidation of bilirubin to biliverdin in vitro and recombinant enzyme (wild type) was obtained by using an overexpression system of the bilirubin oxidase gene with Aspergillus oryzae harboring an expression vector. The absorption and ESR spectra showed that both bilirubin oxidases are multicopper oxidases containing type 1, type 2, and type 3 coppers similar to laccase, ascorbate oxidase, and ceruloplasmin. Site-directed mutagenesis has been performed for the possible ligands of each type of copper. In some mutants, Cys457 --> Val, Ala, His94 --> Val, and His134.136 --> Val, type 1 and type 2 copper centers were perturbed completely and the enzyme activity was completely lost. Differing from the holoenzyme, these mutants showed type 3 copper signals. However, the optical and magnetic properties characteristic of type 1 copper were retained even by mutating one of the type 1 copper ligands, i.e., a mutant, Met467 --> Gly, showed a weak but apparent enzyme activity. A double mutant His456.458 --> Val had only type 1 Cu, showing a blue band at 600 nm (epsilon = 1.6 x 10(3)) and an ESR signal with very narrow hyperfine splitting (A parallel = 7.2 x 10(-)3 cm-1). Since the type 2 and type 3 coppers are not present, the mutant did not show enzyme activity. These results strongly imply that the peculiar sequence in bilirubin oxidase, His456-Cys457-His458, forms an intramolecular electron-transfer pathway between the type 1 copper site and the trinuclear center composed of the type 2 and type 3 copper sites.

Factors contributing to the thermostability of inorganic pyrophosphatase (PPase) were investigated by examining chimeric PPases from Escherichia coli and Thermus thermophilus (Tth). Two chimeric PPase genes, T1-135E (residues 1-135 from the N terminus are comprised of Tth PPase and residues 136-173 are derived from the C terminus of E. coli PPase) and T1-149E [residues 1-149 from the N terminus are from Tth PPase and the rest (150-175) are from E. coli PPase], were constructed by random chimeragenesis. After the genes were overexpressed in the E. coli BL21(DE3) strain and the expression products were purified, we compared the characteristics of these chimeric PPases with those of the parental PPases. We found that the two chimeras had higher activity than either parent PPase at the optimum temperature. We also examined thermal stability in terms of CD spectra, fluorescence spectra, and thermal changes in enzyme activity. The results revealed that the thermal stability of T1-149E is similar to that of Tth PPase, but T1-135E is much more stable. This suggests that the four residues that are different between T1-135E and T1-149E may be critical for thermostability between the two chimeras. By comparing the three-dimensional structures of Tth and E. coli PPases, we deduced that the following two factors may contribute to differences in thermostability. (1) Two residues (Thr138 and Ala141 in the Tth PPase and His140 and Asp143 in the E. coli PPase) in the vicinity of the trimer-trimer interface were different. (2) The Ala144-Lys145 loop in the Tth PPase was deleted in the E. coli PPase and also in the T1-135E chimera. Therefore, we conclude that T1-135E was thermostabilized by these two factors, and also, the Tth PPase moiety may contribute to the structural integrity of the chimeric enzymes.

The complete primary structure of inorganic pyrophosphatase [EC 3.6. 1.1] from Bacillus stearothermophilus (ATCC 12016) was determined at the amino acid level by automated Edman degradation. The subunit of the enzyme consists of 164 amino acid residues with a calculated molecular mass of 18,796. The amino acid sequence of the enzyme is almost identical to that of thermophilic bacterium PS-3. Based on the determined primary structure, a PCR-amplified semi-synthetic gene was constructed and expressed in Escherichia coli JM109. The recombinant Bst. PPase showed the same characteristics and activity as the authentic enzyme, and exhibits higher thermostability than the E. coli enzyme. Furthermore, we prepared tyrosine-substituted variants by site-directed mutagenesis to elucidate the role of two highly conserved tyrosines (Y46 and Y130). As a result, two variants, Y46F and Y130F, lost most of their enzyme activity, whereas their conformations were unaffected. However, the wild-type and two variants exhibited different thermostability behaviors in the presence or absence of Mg2+. Therefore, these tyrosines may contribute to the structural integrity of the active site of the enzyme.

To determine the role of Val75 in the oligomeric structure of trimeric inorganic pyrophosphatase (PPase) [EC 3.6.1.1] from Bacillus stearothermophilus (Bst.), we used site-directed mutagenesis to prepare variants in which Val75 was replaced by Ala, Phe, Leu, Ile, Lys, Gln, and Asp. As a result, the variants in which valine is replaced by hydrophobic residues such as Ala, Phe, Leu, and Ile (V75A, F, L, and I) show almost the same level of enzyme activity and thermostability as the wild type enzyme, whereas variants with hydrophilic residue replacements such as Lys, Gln, and Asp (V75K, Q, and D) showed gross reductions in enzyme activity and thermostability. The dissociation of V75K and V75D from trimer to monomers occurred rapidly as the temperature rose, while V75F, V75L, and V75I dissociated more slowly than the wild type. There was no particular effect of heat treatment on the dissociation of V75A or V75Q, but these variants were slightly dissociated even in the native state. Thus, we conclude that Val75 may locate at the interface between the monomers and its hydrophobic interactions with its surroundings may play a key role in the thermostability and oligomeric subunit interactions of the enzyme.

The genomic DNA encoding the inorganic pyrophosphatase from an extremely thermophilic bacterium, Thermus thermophilus HB8 (ATCC27634), was isolated by colony hybridization with a probe designed as a part of gene amplified by the PCR method, which was derived from the partial amino acid sequence of the enzyme. The DNA was cloned into a plasmid vector, pUC118, after digestion with BamHI. The inserted nucleotide fragment was about 1.8 kbp in length and the nucleotide sequence included a 525 bp open reading frame. The deduced amino acid sequence was completely identical with that of the enzyme determined by automated Edman analysis of peptide fragments isolated from digests obtained with Staphylococcus aureus V8 protease and Achromobacter protease I, and also from products obtained on chemical cleavage with cyanogen bromide and 70% formic acid. The subunit of this enzyme is composed of 174 amino acid residues with a calculated molecular weight of 19,084. Then, the gene was overexpressed in Escherichia coli BL21 (DE3) using a plasmid vector, pET15b, system. The recombinant enzyme was fully active, and exhibited higher thermostability than the E. coli enzyme. Amino acid residues located on the surface of the recombinant enzyme were determined by means of limited proteolysis, and the results revealed that the environment of Lys residues is almost the same as the crystal structure reported previously [Teplyakov, A. et al. (1994) Protein Sci. 3, 1098-1107]. Furthermore, the roles of two tryptophan residues were investigated by site-directed mutagenesis, which indicated that they may be responsible for the structural integrity and thermostability.

The solution structure of a human cystatin A variant, cystatin A2-98 M65L, which maintains the full inhibitory activity of the wild-type protein, was determined at pH 3.8 by sD/3D heteronuclear double- and triple-resonance NMR spectroscopy. The structure is based on a total of 1343 experimental restraints, comprising 1139 distance, 154 phi and chi 1 torsion angle restraints, and 50 distance constraints for 25 backbone hydrogen bonds. A total of 15 structures was calculated using the YASAP protocol with X-PLOR, and the atomic rms distribution about the mean coordinate positions for residues 8-93 was 0.55 +/- 0.10 A for the backbone atoms and 1.05 +/- 0.11 A for all heavy atoms. The structure consists of five antiparallel beta-sheets and two short alpha-helices. Comparison with the X-ray structure of cystatin B in the papain complex shows that the conformation of the first binding loop is quite similar to that of cystatin A, with an rms deviation of 0.78 A for the backbone atoms in the 43-53 region (cystatin A numbering). The second binding loop, however, is significantly different in the two structures, with an rms deviation greater than 2 A. There are some other significant differences, especially for the N-terminal and alpha-helix regions. The overall structure of cystatin A is also compared with the recently reported NMR structure of the wild-type cystatin A (stefin A) at pH 5.5 (Martin et al., 1995) and reveals the following features. that differ in our structure from the previous one: (1) the N-terminal segment, which was unstructured in the previous report, folds over in close vicinity to the C-terminus, as revealed by the distinctive NOEs between those segments; (2) two discrete short alpha-helices linked by a type II reverse turn were found, instead of the continuous single alpha-helix with a slight kink shown in the previous structure; (3) the second binding loop, which was not well converged in the previous study at pH 5.5, is determined very well in our structure. The effect of the N-terminal truncation on the cystatin A structure was examined by comparing the 1H-15N HSQC spectrum of cystatin A2-98 with that of the cystatin A5-98 variant, which lacks the anti-papain activity, revealing significant chemical shift differences in the residual N-terminal segment and the first binding loop, together with small shifts in the other parts.(ABSTRACT TRUNCATED AT 400 WORDS)

Lens crystallins from the African ostrich (Struthio camelus) were isolated and characterized. Four crystallin fractions corresponding to alpha-, delta/beta- and beta-crystallins similar to those of duck crystallins were isolated, but epsilon-crystallin was found to be absent. The native molecular masses and subunit structures of the purified fractions were analysed by gel filtration. SDS/PAGE and isoelectric focusing, revealing various extents of heterogeneity in each orthologous crystallin class. An ion-exchange chromatographic method was used for the large-scale preparation of delta-crystallin suitable for structural and enzymic studies. It was unexpectedly found that the purified native delta-crystallin of ostrich lens possessed high argininosuccinate lyase activity, in contrast with chicken delta-crystallin. The c.d. spectra indicated a predominant beta-sheet structure in alpha- and beta-crystallins, and a significant contribution of alpha-helical structure in the delta-crystallin fraction. The estimate of secondary structures from c.d. spectroscopy for each crystallin class bears a resemblance to that of duck crystallins, except that ostrich delta-crystallin possesses much less helical content than duck delta-crystallin. Comparison of crystallin compositions and structures from aquatic and terrestrial birds revealed distinct differences.

The complete amino acid sequence of the inorganic pyrophosphatase from thermophilic bacterium PS-3 was determined by automated Edman analysis of the intact protein and of peptides derived from digests obtained with lysylendopeptidase, Staphylococcus aureus strain V8 protease, and arginylendopeptidase. The monomer peptide chain comprises 164 amino acid residues and has a calculated molecular weight of 18,792. The sequence is identical at about 46% of the amino acid positions with that of the Escherichia coli enzymes.

Subcellular distribution of catalase for porcine kidney was analyzed by differential centrifugation of kidney homogenate. The specific activity of catalase was the highest in light mitochondrial fraction, followed by mitochondrial, cytosolic, nuclear, and microsomal fractions. However, about a half of the total activity was found in supernatant (cytosol) fraction and the other half was mainly associated with both mitochondrial and light mitochondrial fractions. Osmotic shock using hypotonic solution, 50 mm sodium phosphate buffer (pH 7.0) was found to be most effective for solubilization of particulate-bound catalase. Both particulate and cytosol catalases from porcine kidney were purified by ammonium sulfate fractionation followed by DEAE-cellulose, CM-cellulose, and Sephadex G-100 column chromatographies. The purified enzymes showed two distinct bands, one major and the other minor, on disc gel electrophoresis. Both particulate and cytosol enzymes showed identical molecular weights estimated from disc gel electrophoresis; that of the major component was 219,000 corresponding to native molecule and that of the minor one 421,000. A similar value, 210,000, was also obtained for the major component by gel filtration on a Bio Gel A-1.5 m column. It was inferred that the minor component was formed by dimerization of native molecule caused by formation of disulfide cross-links due to oxidation of SH groups in protein moiety. The particulate and cytosol catalases showed essentially identical molecular characteristics, although a slight difference was detected in stability in guanidine-HCl solution. The effect of NaCl on enzyme activity and optical properties of catalase were also measured.

Chemical modifications by photooxidation in the presence of rose bengal (RB) and with tetranitromethane (TNM) were carried out to elucidate the amino acid residues involved in the active site of inorganic pyrophosphatase (pyrophosphate phosphohydrolase) [EC 3.6.1.1] from Escherichia coli Q13. The photooxidation caused almost complete inactivation, which followed pseudo-first-order kinetics depending on pH and concentration of RB. The presence of Mg2+ or complex between Mg2+ and substrate or substrate analogues, imidodiphosphate and sodium methylenediphosphate, gave partial protection against the photoinactivation, whereas the substrate alone showed no protective effect. The enzyme was almost completely inactivated by chemical modification with TNM, depending upon the concentration of TNM. The amino acid analyses and enzyme activity measurements revealed that 2 histidyl residues among 5 photooxidized residues and 2 tyrosyl residues per subunit were essential for the enzyme activity. The circular dichroism (CD) spectra in the far ultraviolet region showed no significant alteration during these two modifications, indicating that the polypeptide chain backbone of the enzyme remained unaltered. However, the modifications altered considerably the CD bands in the near ultraviolet region and the fluorescence spectra, indicating that subtle change in conformation had occurred in the vicinity of the active site in the enzyme molecule. These results strongly suggest that histidyl and tyrosyl residues may be involved in the active site or be located in the vicinity of the active site and seem to participate in the mechanism of stability against heat inactivation.

Bilirubin oxidase [EC 1.3.3.5], purified from the culture medium of Myrothecium verrucaria, was found to contain two blue copper atoms per protein molecule with a molecular weight of ca. 52 kDa. The two copper atoms were estimated to be in the all cupric state by the cuproine colorimetric method and also atomic absorption analysis. We could remove the reduce cuprous ions from the holo enzyme by adding ascorbate, followed by a KCN solution, yielding an apo-enzyme with no activity. The apo-enzyme can be reconstituted with Cu or other divalent cations such as Co, Fe, and Cd, with accompanying recovery of the enzyme activity. The activity recovery depended upon the species of cation employed; Cu being most effective, an almost 100% recovery, and Cd the least, only a 25% recovery. We could obtain information on the copper ions and their coordination structure by spectroscopic analyses of the apo- and reconstituted enzymes, obtaining such as absorption, CD, MCD, and XPS spectra. The bilirubin oxidase catalyzed-reaction was a second order reaction with respect to copper bound with protein. The donor set was of the CuSS*N2 (S = Cys, S* = Met, N = His) type, i.e., the same as in the case of blue copper proteins. On studying the Co-substituted enzyme, it was revealed that the copper site of the enzyme had a 4-coordinated structure.

Porcine erythrocyte catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase, EC 1.11.1.6) has been purified from porcine blood by DEAE-cellulose column chromatography, ammonium sulfate fractionation and CM-cellulose column chromatography. The purified enzyme was found to associate into larger molecules than the native one when it was stored at 4°C for more than one week. The associated molecules can be detected by gel filtration on a Bio-gel A-1.5 m column and disc gel electrophoresis as well as ultracentrifugal analysis. Molecular weights of the associated catalase molecules were about 500 000, 750 000, 1 000 000 and so forth estimated by gel filtration and disc gel electrophoresis, corresponding to dimer, trimer and tetramer respectively, of a native molecule (monomer) with a molecular weight of about 250 000. The association of catalase molecules is found to be time-dependent and to proceed seemingly from monomer through dimer as an intermediate. From the effects of several thiol reagents or reducing reagents on the association process and spectrophotometric titration of SH groups, it is inferred that this specific association of porcine erythrocyte catalase is caused by formation of intermolecular disulfide cross-links due to air oxidation of SH groups in the protein moiety.

We have studied the primary structure of human cystatin As from epidermis, liver, spleen, and leukocytes. These molecules were indistinguishable on PAGE in the presence and absence of SDS, by fast protein liquid chromatography (FPLC) chromatofocusing on a Mono P column, and in amino acid composition. The NH2- and COOH-terminal amino acid sequences of human cystatin As from epidermis, liver, and spleen were identical with those of human leukocyte cystatin A previously reported except for the lack of the NH2-terminal methionine residue in human epidermal cystatin A. The peptides obtained upon digestion of four human cystatin As with Achromobacter protease I (AP) showed identical peptide maps on HPLC except for different retention times of the NH2-terminal peptides. Furthermore, the amino acid compositions of corresponding separated peptide quartets were identical. We also determined the complete amino acid sequence of human epidermal cystatin A by sequencing peptides obtained from AP digestion and cyanogen bromide (CNBr) cleavage. It consisted of 97 amino acid residues, and was identical with those of human cystatin As from liver, spleen, and leukocytes except for the lack of the NH2-terminal methionine residue.

Two low-molecular-weight thiol proteinase inhibitors, TPI(1) and TPI(2), were purified from newborn rat epidermis by homogenization and extraction at 37 degrees C, followed by lyophilization, Sephadex G-75 gel filtration and DEAE-cellulose column chromatography. Both purified inhibitors were shown to be homogeneous by polyacrylamide gel electrophoresis in the presence and absence of SDS. TPI(1) was more anionic than TPI(2), and the molecular weights of TPI(1) and TPI(2) were determined to be ca. 12,000 and 13,000, respectively. They were highly specific for thiol proteinase; TPI(1) was especially more effective than TPI(2) on the proteolytic activity of casein and hydrolytic activity of papain on authentic substrates, and a similar but lesser effect was detected for ficin. They inhibited the enzyme in a noncompetitive manner with inhibition constants of 6.01 X 10(-8) M and 4.57 X 10(-7) M for TPI(1) and TPI(2), respectively, calculated from the BAPA hydrolytic activity of papain. Both inhibitors were quite stable proteins as to heat and extreme pHs. The amino acid composition of TPI(1) and TPI(2) were slightly different from each other, and both inhibitors contained no cysteinyl or cytinyl residue and trptophanyl residue. From these results, TPI(1) and TPI(2) seem to be iso-inhibitors. The absorption and CD spectra of TPI(1) and TPI(2) in the near ultraviolet region indicated that the conformation in the vicinity of aromatic amino acid residues in TPI(1) was slightly different from that of TPI(2). The CD spectra of both inhibitors in the far ultraviolet region showed the presence of the beta turn structure in the protein moiety, suggesting some important roles of the beta turn of both inhibitors in the interaction with the thiol enzymes.

The inactivating effects of halide ions on porcine kidney catalase were investigated. It was found that the inactivation of catalase was dependent on incubation time with halides and on their concentrations: the addition of 2 M NaCl reduced the activity to 18% of the original level, whereas the same extent of inactivation was obtained in the presence of 0.1 M NaF. Removal of excess halide ions by dialysis resulted in good recovery of enzyme activity for all halides examined except for KI. Additions of halide ions to catalase solution caused subtle but evident alterations in the absorption and CD spectra. We could detect clear difference spectra between the salt-treated and native catalase solutions. These difference spectra showed halide concentration dependence with an evident isosbestic point. From these changes and also changes in CD spectra, we deduced that fluoride, chloride, and bromide ions can bind with heme iron of the catalase molecule as ligands to form stable catalase-halide complexes, but iodide ions showed a different reactivity with catalase from other halides and may cause gross alteration in the structure or conformation of catalase. Dissociation constants (Kd) were estimated to be 2.5, 0.23, and 26 M for chloride, fluoride, and bromide complexes with catalase, respectively, and there is no heme-heme interaction during formation of the catalase-halide complexes as estimated from the Hill plot.

Inorganic pyrophosphatases (PPiases) from both yeast and Escherichia coli were found to be stable against heat denaturation in the presence of Mg2+, as previously observed with the enzymes from thermophilic bacteria. No loss of activity was observed after 1 h of incubation at 50 °C and pHs between 6 and 9 in the yeast enzyme, and at 60 °C and pHs between 7.2 and 9.2 in the E. coli enzyme. Such an induced thermostability of the E. coli enzyme was detected when Mn2+, Co2+, Ca2+, Cd2+, and Zn2+ were added in place of Mg2+. On the other hand, the degree of induced thermostability of the yeast enzyme was dependent upon the divalent cations used, and Ni2+ and Cu2+ accelerated the heat inactivation. On adding the divalent cations, the difference spectra of the E. coli enzyme always showed negative peaks in the ultraviolet region, but those of the yeast enzyme changed again depending upon the divalent cations. The circular dichroism spectra in the near ultraviolet region of both enzymes greatly differed from each other, but both were not affected so much by adding the divalent cations unlike the thermophilic enzymes from Bacillus stearothermophilus and thermophilic bacterium PS-3. Yeast and E. coli PPiases did not cross-link with the anti-immunoglobulin G's from the thermophilic enzymes, but the thermophilic enzymes did with each other's antisera. The results in the present study indicated that the conformation of PPiase, in which the aromatic amino acid residues were buried in the interior of the protein molecule, was very important for the thermostability and also that the protein structures of PPiases from B. stearothermophilus and thermophilic bacterium PS-3 were very similar to each other, but were very different from those of the mesophilic enzymes.

Photooxidation of inorganic pyrophosphatase [pyrophosphate phosphohydrolase EC 3.6.1.1] from Bacillus stearothermophilus in the presence of rose bengal resulted in rapid loss of enzymatic activity. The pH profile of the inactivation rate by the photooxidation showed an inflection point around pH 6.8, suggesting the involvement of histidyl residues in the inactivation. Amino acid analysis revealed that the loss of enzymatic activity was accompanied by the destruction of 3 histidyl residues per molecule. The presence of Mg2+ alone afforded partial protection against the inactivation, whereas inorganic pyrophosphate, the substrate, showed almost no protective effect against inactivation. The photooxidation of inorganic pyrophosphatase altered the circular dichroism spectrum and the difference UV spectrum induced by Mg2+ in the near ultraviolet region. These results suggested that histidyl residues appear to be located at the binding site of Mg2+ and may contribute to the conformational change induced by Mg2+.

The dissociation of porcine erythrocyte catalase [EC 1.11.1.6] into subunits on denaturation with alkali, GuHCl and urea was investigated by following the changes in hydrodynamic properties, absorption and CD spectra in the Soret region and inactivation of the enzyme. It was found that dissociation proceeded in an "all or none" manner from the native tetramer (molecular weight, ca. 250,000) into identical 1/4-sized monomers (molecular weight, ca. 54,000 with alkali, 65,000 with urea and 71,000 with GuHCl) as estimated by ultracentrifugal analyses. On this dissociation, the sedimentation coefficient decreased from about 11S to 5.1 - 3.7S, and absorption spectra in the Soret region decreased to about 40% of the native level and showed a broad band around 365-375 nm and a shoulder around 415-420 nm; these changes were accompanied by complete loss of enzyme activity. The change in enzyme activity correlated well with that of absorption and CD spectra in the Soret region, depending on denaturation time, alkaline pH used and concentration of both denaturants. The reassociated catalase obtained by removing urea by dialysis was characterized by recovery of distinct CD bands in the Soret and near ultraviolet regions, although the partial refolding of alpha-helical conformation occurred without recovery of enzyme activity. These results indicate that the conformational changes and dissociation process of catalase into subunits can be monitored spectrophotometrically in relation to enzyme activity, and that subtle conformations near the heme groups and polypeptide backbone play an important role in maintaining full enzyme activity of the catalase molecule.

The conformational changes of the papain molecular on interaction with two thiol proteinase inhibitors (TPI(1) and TPI(2] from newborn rat epidermis were studied by measuring circular dichroism (CD), the difference absorption spectrum, and the fluorescence spectrum due to tryptophan residues in papain. The far-ultraviolet CD band of papain between 210 and 230 nm was distinctly reduced on interaction with both inhibitors. Also, the near-ultraviolet CD spectrum of TPI(1)-bound papain changed between 285 and 320 nm as well as that of the TPI(2)-bound enzyme. The difference absorption spectrum for TPI(1)-bound papain exhibited two distinct peaks at 276.5 and 282 nm, indicating perturbation of aromatic amino acid residues. The fluorescence intensity of papain was significantly decreased on interaction with both inhibitors, which showed pH-dependency on an ionizable group, with pK values of 8.5 and 7.9 for TPI(1) and TPI(2), respectively. The complex formation of papain with both inhibitors caused a reduction of the susceptibility of a tryptophan residue, probably tryptophan-177, to chemical modification with N-bromosuccinimide. These results suggest that the active site involving histidine-159 in the papain molecule was much influenced by the alteration of the microenvironment of tryptophan-177 as a part of the interaction site for these two thiol proteinase inhibitors.

A synthetic gene containing the coding sequence for the human cysteine proteinase inhibitor, cystatin A, was obtained by enzymatic assembly of 20 oligodeoxyribonucleotides which had been chemically synthesized by the solid phase phosphoramidite method. It was cloned into an Escherichia coli plasmid. The expression plasmid for cystatin A was constructed by introducing the synthetic gene downstream of the tac promoter of an E. coli plasmid which is a derivative of pKK223-3 with high copy number. The gene was expressed in E. coli JM109 without IPTG-induction. The expression of cystatin A was detected by SDS-polyacrylamide gel electrophoresis of the E. coli JM109 lysate, followed by immunoblotting using rabbit antiserum raised with human epidermal cystatin A and alkaline phosphatase-conjugated goat anti-rabbit IgG. The result showed that the molecular weight of the expression product is identical with that of the authentic protein and the antigenic properties are also the same. Furthermore, the expression product purified with a CM-papain Sepharose affinity column and FPLC system with a Mono-Q column showed the same inhibitory activity for various cysteine proteinases. Also, purified recombinant cystatin A was found to have identical amino acid composition, NH2-terminal amino acid sequence, and peptide-map on reverse phase HPLC with those of the authentic inhibitor.

The process of activation to peroxidase due to the complexing between hematin and chelating reagents (pyridine, histidine, arginine, guanidine, formamide, acetate, and methanol) were studied by measuring both enzymic activity and spectral change as a function of reagent concentration. A large spectral change occurs when a hematin complex carrying two moles of a reagent is formed from hematin. On the other hand, the complexes active as peroxidase carry more than two moles of reagent; two moles on the ferric iron atom of hematin and others, probably, on the protoporphyrin ring. Histidine and arginine are effective in activating hematin, while other essential amino acids are ineffective. The values of k 4 (rate constant for the reaction with hydrogen donor) for the active nonprotein complexes are comparable to or one order less than those for common peroxidases, whereas the values of k 1 (rate constant for the reaction with H 2 O 2 ) are much smaller than the k 1 values for peroxidases. The role of the apoproteins of peroxidases is discussed in connection with the results obtained for the hematin complexes.

Optical rotatory dispersions between 200 and 600 mμ are presented for mononucleosides and 5′-mononucleotides in neutral, acid, and in some cases alkaline solutions. All display a single Cotton effect in the ultraviolet region (above 220–240 mμ); the purine ones are negative in sign and the pyrimidine ones positive, with the crossovers (zero rotations) in most cases close to the wavelengths of their respective absorption maxima. The visible rotatory dispersions obey the one-term Drude equation, except for TMP and UMP, which show anomalous dispersions. The rotational strengths of the dichroic bands were estimated from the Cotton effect profiles; cytosine mononucleotides and mononucleotides show the strongest rotational strengths among the compounds studied.