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The substrate specificity of beta-collagenase from Clostridium histolyticum has been investigated by measuring the rate of hydrolysis of more than 50 tri-, tetra-, penta-, and hexapeptides covering the P3 to P3' subsites of the substrate. The choice of peptides was patterned after sequences found in the alpha 1 and alpha 2 chains of type I collagen. Each peptide contained either a 2-furanacryloyl (FA) or cinnamoyl (CN) group in subsite P2 or the 4-nitrophenylalanine (Nph) residue in subsite P1. Hydrolysis of the P1-P1' bond produces an absorbance change in these chromophoric peptides that has been used to quantitate the rates of their hydrolysis under first order conditions ([S] much less than KM) from kcat/KM values have been obtained. The identity of the amino acids in all six subsites (P3-P3') markedly influences the hydrolysis rates. In general, the best substrates have Gly in subsites P3 and P1', Pro or Ala in subsite P2', and Hyp, Arg, or Ala in subsite P3'. This corresponds well with the frequency of occurrence of these residues in the Gly-X-Y triplets of collagen. In contrast, the most rapidly hydrolyzed substrates do not have residues from collagen-like sequences in subsites P2 and P1. For example, CN-Nph-Gly-Pro-Ala is the best known substrate for beta-collagenase with a kcat/KM value of 4.4 X 10(7) M-1 min-1, in spite of the fact that there is neither Pro nor Ala in P2 or Hyp nor Ala in P1. These results indicate that the previously established rules for the substrate specificity of the enzyme require modification.

The relationship between the six collagenases (alpha, beta, gamma, delta, epsilon, and zeta) isolated and characterized in the preceding papers [Bond, M.D., & Van Wart, H.E. (1984) Biochemistry (preceding two papers in this issue)] has been investigated. Chemical modification reactions establish that all six enzymes contain essential carboxyl, tyrosine, and lysine residues. Circular dichroism spectra of the peptide bond region show that the secondary structures of the collagenases are very similar. Ouchterlony double-immunodiffusion experiments carried out with antiserum prepared against beta-collagenase indicate that all six collagenases are cross-reactive. Reverse-phase high-pressure liquid chromatography elution profiles of tryptic digests of these collagenases and sodium dodecyl sulfate electrophoresis gels of the peptides formed on reaction with cyanogen bromide have been obtained. The results indicate that the class I collagenases have extensive sequence homology with each other and that the class II collagenases have extensive sequence homology with each other but that the enzymes in the two classes have substantially different sequences. In addition, the data show that beta-collagenase probably consists of domains that have homologous amino acid sequences, which may have arisen by full or partial intragenic gene duplication. This may account for the unusually high molecular weight of this and the other collagenases. Finally, on the basis of the similarities between the collagenases in the two classes, it is suggested that one class evolved from the other by gene duplication followed by independent evolution by point mutations to yield enzymes with different substrate specificities.

The six collagenases (alpha, beta, gamma, delta, epsilon, and zeta) from Clostridium histolyticum isolated in the preceding paper [Bond, M. D., & Van Wart, H. E. (1984) Biochemistry (first paper of three in this issue)] have been characterized in detail. The molecular weights determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis range from 68 000 to 125 000. Isoelectric focusing experiments demonstrate that the isoelectric points of the collagenases are in the 5.35-6.20 range. These experiments also reveal that the subspecies of alpha- and gamma-collagenases (alpha1 vs. alpha 2 and gamma 1 vs. gamma 2) have different isoelectric points but the same molecular weights. Microheterogeneity is also observed for the beta- and epsilon-collagenases. The amino acid compositions of all six collagenases have been determined, and analysis for neutral sugars and hexosamines shows that none of the enzymes have a significant carbohydrate content. Zinc and calcium are the only metals that copurify with the collagenases. The purified enzymes contain approximately 1 mol of zinc/mol of protein and a calcium content that varies from about 2 mol/mol for alpha-collagenase to about 7 mol/mol for beta-collagenase. All of the collagenases are 5-10 times more active against gelatin than collagen. The alpha-, beta-, and gamma-collagenases are significantly less active toward the synthetic peptide substrates examined than the delta-, epsilon, and zeta-collagenases. This property, taken together with data on the stabilities and amino acid compositions of these enzymes, strongly supports their assignment to two distinct classes. This establishes clearly that C. histolyticum does, indeed, produce more than one different type of collagenase.

Six collagenases present in the culture filtrate of Clostridium histolyticum have been purified to homogeneity. Chromatography over hydroxylapatite, Sephacryl S-200, and L-arginine-Affi-Gel 202 removes the brown pigment and the great majority of the contaminating proteinases active against casein, benzoyl-L-arginine ethyl ester, and elastin. Reactive Red 120 dye ligand chromatography subdivides the collagenases, which have very similar physicochemical properties, among four fractions. The final purification is achieved by chromatography over DEAE-cellulose and SP-Sephadex. All six collagenases, designated alpha, beta, gamma, delta, epsilon and zeta by the order of their purification, are highly active against collagen and devoid of other proteolytic activities. Each exhibits a single band on sodium dodecyl sulfate-polyacrylamide gels. Two distinct subspecies of the alpha and gamma enzymes have been isolated, which have the same molecular weight and activity but different isoelectric points. There is some less pronounced microheterogeneity for the other collagenases. On the basis of their activities toward native collagen and the synthetic peptide 2-furanacryloyl-L-leucylglycyl-L-prolyl-L-alanine (FALGPA), the six collagenases are divided into two classes. Class I collagenases (alpha, beta, and gamma) have high collagenase activity and moderate FALGPA activity while the class II collagenases (sigma, epsilon, and sigma) have moderate collagenase and high FALGPA activities. The relationship between these six collagenases and other reported to have been isolated in the literature has also been examined.

A versatile, convenient assay for vertebrate collagenases has been developed using the fluorescent peptide substrate dansyl-Pro-Gln-Gly-Ile-Ala-Gly-D-Arg. This sequence resembles that of collagen at the site of cleavage but includes modifications designed to eliminate nonspecific hydrolysis by contaminating peptidases. Both human skin fibroblast and bovine corneal cell collagenases cleave the substrate specifically at the Gly-Ile bond. Plasmin, thrombin, trypsin, alpha-chymotrypsin, carboxypeptidase B, and bacterial collagenase do not cleave the substrate. Elastase and angiotensin converting enzyme display 20- and 400-fold less activity than the vertebrate collagenases, respectively, and cleave the peptide at different positions. The assay is performed by incubating a 5- to 25-microliters aliquot of trypsin-activated sample with an equal volume of 2 mM substrate overnight at 33 degrees C and pH 7.5. Thin-layer chromatography then separates the fluorescent product from the substrate in less than 20 min and allows the detection of subnanogram levels of collagenase. The assay is applicable to the screening of large numbers of samples under different conditions of pH and ionic strength and is readily adaptable for use in a variety of collagenase-dependent systems, such as assays for collagenase activating and/or inducing factors.