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Summary The incidence of skin cancer, which often affects the facial skin, has risen worldwide. After resecting such facial lesions, plastic reconstruction is necessary in most cases. The paramedian forehead flap (PFF) and the bilobed flap (BF) are commonly used for nasal reconstruction, but whether patients and physicians are satisfied with the esthetics is undetermined? In this study, scar questionnaires (Manchester Scar Scale, Vancouver Scar Scale, and Patient and Observer Scar Assessment Scale) and optical three-dimensional (3D) imaging were used for subjective and objective evaluation of esthetical outcomes after plastic reconstruction of the nose in 30 patients. The distances between landmarks and changes in volume between the treated and both the mirrored, healthy side of the face as well as an untreated, matched control group were measured using the optical (3D) scans. The questionnaires ascertained whether the patient was content with the esthetical outcome of both flaps. In the opinion of the observer, the esthetical outcome of both flaps was sufficient; only a few of the measured distances differed significantly between the patients and the control group. However, the measured volume differences of the donor site of the flap differed significantly between the PFF group and the control group (p = 0.0078). The BF was used for smaller defects, while the PFF was used for major defects. Besides a greater donor-side morbidity for the PFF, both flaps led to esthetically sufficient results and could be used for the reconstruction of the nose depending on the defect size and localization.

The trigger factor is associated with bacterial ribosomes and catalyzes proline-limited protein folding reactions. Its folding activity is very high and conserved in evolution, as shown for the homologous enzymes from Escherichia coli and Mycoplasma genitalium. The folding protein substrate (a variant of ribonuclease T1) binds with high affinity to the trigger factors, and permanently unfolded proteins are strong, competitive inhibitors. We used this inhibition to characterize the substrate binding sites of the trigger factors. Unfolded α-lactalbumin binds very tightly and inhibits the trigger factor from M. genitalium with a KI value of 50 nM. The binding of inhibitory proteins is independent of proline residues, as shown for unfolded tendamistat, which binds to the trigger factor with equal affinity in the presence and in the absence of its three proline residues. The good inhibition by a non-folding variant of ribonuclease T1 that lacks Pro39 showed that this proline, at which the catalysis of folding occurs, is dispensable for substrate binding. The trigger factors cannot catalyze prolyl isomerization when proteins are partially folded already. They preferentially recognize unstructured protein chains, which bind with high affinity to a site distinct from the catalytic prolyl isomerase center in the FKBP domain.

In the absence of its two disulfide bonds, ribonuclease T1 can exist in a native-like folded conformation when > or = 2 M NaCl is present. We measured the kinetics of unfolding and refolding of two reduced and carboxymethylated variants of ribonuclease T1 with one cis proline (the Ser54Gly/Pro55Asn variant) and with two cis prolines (the wild-type protein) as a function of the NaCl concentration. Single and double mixing techniques were used. Analysis of the kinetic results demonstrates that the two cis prolyl bonds at Pro39 and Pro55 remain cis in the folded state after the reduction and carboxymethylation of the disulfide bonds. Folded molecules with trans isomers could not be found. The substitution of cis-Pro55 influences the proline-limited folding reaction, and the analysis of the changes in the folding kinetics shows that the trans-->cis isomerizations of both prolines are slow and are rate-determining steps for the refolding of ribonuclease T1 in the presence as well as in the absence of the disulfide bonds. The direct folding reaction of protein chains with correct prolyl isomers is also affected by the Ser54Gly/Pro55Asn mutation. The rate of refolding is decreased, whereas the rate of unfolding is almost unaffected. The kinetic analysis points to two main consequences of the Ser54Gly/Pro55Asn mutation for the stability and the folding mechanism of RNase T1. It is moderately destabilizing, because the deletion of a conformationally restricted residue (Pro55-->Asn) and the insertion of a flexible residue (Ser54-->Gly) both tend to increase the entropy of the unfolded state. The cis trans isomerization of Pro55 is abolished, however, leading to a decrease in the entropy of the unfolded protein. These two entropic contributions seem to partially compensate each other, and the net change in free energy as a consequence of the Ser54Gly/Pro55Asn double mutation is very small.

Disulfide bonds in a folding protein chain are equivalent to prematurely formed native-like tertiary interactions. We investigated whether the mechanism of protein folding is changed by the presence of disulfide bonds. As a model we used the S54G/P55N-variant of ribonuclease T1, a protein with two disulfide bonds and a single cis proline (Pro39), and we measured both the direct and the proline-limited folding reactions before and after breaking of the disulfide bonds. The folding kinetics were compared under refolding conditions, in the regions of the area-induced unfolding transitions of the two forms, and under folding conditions. The kinetics in the transition regions were analyzed on the basis of a three-species mechanism and all microscopic rate constants of folding and of prolyl isomerization could be determined as a function of the area concentration from the measured rates and amplitudes. These kinetic analyses indicated that the disulfide bonds can be rather unfavorable for the folding of S54G/P55N-ribonuclease T1. Under strongly native conditions they retard the rate-limiting trans → cis isomerization of Pro39 because they allow the rapid formation of partially ordered structure prior to the proline-limited refolding reaction. Under unfolding conditions the isomerization of Pro39 is not affected. The direct unfolding and refolding reactions in the transition region of polypeptide chains with correct prolyl isomers are also decelerated when the disulfide bonds are present. These changes in the folding kinetics are possibly related to the decrease in chain flexibility that is caused by the disulfide bonds. A high flexibility is probably important throughout folding, and in the case of ribonuclease T1 a premature locking of tertiary contacts by intact disulfide bonds can interfere unfavorably with both the direct and the proline-limited folding reactions.

We present a kinetic method to determine the concentration of native molecules in protein folding transitions. It is based on the observation that frequently native protein molecules unfold slowly when transferred to unfolding conditions, whereas folding intermediates unfold rapidly. The fraction of native molecules in a folding transition can thus be determined by kinetic unfolding assays in a two-step procedure. Aliquots of the protein are first equilibrated at different concentrations of denaturant and then transferred to constant unfolding conditions to determine the amplitude of unfolding. This amplitude is a direct measure for the concentration of native molecules in the sample. The two-state character of a solvent-induced unfolding transition can thus be examined. When the fractional change of a spectral property in a transition follows the decrease in the concentration of the native molecules, as measured by the unfolding assays, then the presence of intermediates that differ from the unfolded protein in this property can be definitely excluded. This test complements the calorimetric test for intermediates in thermal unfolding transitions. By using this method, we show that the NaCl-induced folding transition of the reduced and carboxymethylated form of a variant of ribonuclease T1 is well described by the two-state approximation. In the unfolding of apo-alpha-lactalbumin, the measured profile for the native protein coincides with the fluorescence-detected transition, but not with the transition that is monitored by amide circular dichroism. This confirms that a partially folded intermediate is present in the folding transition of apo-alpha-lactalbumin.

In a recent publication in this journal (1), the mechanisms, detection and prevention of gammopathy interference in clinical chemistry assays were discussed. Here, we report a case in which a monoclonal gammopathy was detected by measurement of the semi-quantitative serum indices on a MODULAR ANALYTICS P module (Roche Diagnostics, Mannheim, Germany). For the serum index measurement, 8 mL of sample are mixed with 200 mL of saline and absorbances at 480, 505, 570, 600, 660 and 700 nm are measured. From these absorbance values, semi-quantitative results are calculated for the degree of lipemia, hemolysis and icterus present in the sample. The degree of lipemia can be more precisely described as the degree of turbidity in the sample. The lipemia index is equivalent to the concentration of Intralipid , up to a linearity limit of 1000 mg/dL. A 50-year-old female patient was admitted to hospital for loss of consciousness, subsequent collapse

Monoclonal gammopathy is characterized by the presence of an M-protein in serum or urine that has homogeneous structural and functional properties. It can occur in very high concentrations and may cause significant interference in clinical chemistry assays. Examples of gammopathy interference for the analytes glucose, bilirubin, gamma-glutamyltransferase, urea and ferritin are presented. Various mechanisms of interference are described, such as the production of turbidity by the M-protein and the binding of the M-protein to a component of the test system or analyte. In immunoglobulin tests, the M-protein is the analyte itself and may not be completely bound by the test antibody owing to its structural properties. Modern analyzers can detect unusual changes in absorption during the course of a reaction, and thus the formation of turbidity due to M-proteins. This interference may be prevented by optimizing the buffering conditions of the reagents to avoid the formation of turbidity or by removal of the M-protein prior to analysis of the sample. Owing to the unique properties of each M-protein, it is impossible to protect common clinical chemistry test systems completely from gammopathy interference. Therefore, efficient ways for the detection of such interference are needed.

Publisher Summary This chapter discusses the function of prolyl isomerases in protein folding. The importance of prolyl isomerization reactions as slow, rate-limiting steps of folding, and their interdependence with other events in protein folding are described. Some experimental data on the catalysis by prolyl isomerases of various slow in vitro protein folding reactions are reviewed. The enzymatic functions of prolyl isomerases in vitro are fairly well characterized. They catalyze cis-trans isomerizations of Xaa-Pro bonds in small peptides and some proline-limited steps in the slow folding of several proteins. The characterization of the molecular nature of rate-limiting steps is a major aim in the elucidation of the folding mechanism of proteins. Folding reactions that involve prolyl isomerization are identified by measuring their kinetic properties and by comparing them with the properties of prolyl isomerization in short peptides. The chapter also explores the results that possibly suggest a role for prolyl isomerases in cellular folding and a close inter-relationship with disulfide bond formation. The efficiencies of various prolyl isomerases as catalysts of the slow-folding reactions of different proteins under varying folding conditions are tabulated.

Prolyl isomerases are able to accelerate slow steps in protein refolding that are limited in rate by cis/trans isomerizations of Xaa-Pro peptide bonds. We show here that prolyl isomerizations in the course of protein unfolding are also well catalyzed. To demonstrate catalysis we use cytoplasmic prolyl isomerase from Escherichia coli as the enzyme and reduced and carboxymethylated ribonuclease T1 as the substrate. This form of ribonuclease T1 without disulfide bonds is nativelike folded only in the presence of moderate concentrations of NaCl. Unfolding can be induced by reducing the NaCl concentration at ambient temperature and in the absence of denaturants. Under these conditions prolyl isomerase retains its activity and it catalyzes prolyl cis/trans isomerization in the unfolding protein. Under identical conditions within the NaCl-induced transition unfolding and refolding are catalyzed with equal efficiency. The stability of the protein and thus the final distribution of unfolded and folded molecules attained at equilibrium is unchanged in the presence of prolyl isomerase. These results demonstrate that prolyl isomerase functions in protein folding as an enzyme and catalyzes prolyl isomerization in either direction.