Effects of structure-forming solutes on chicken egg white lysozyme after reductive cleavage of disulfide bonds

Aggregate formation and the structure of the aggregates of disulfide-reduced proteins

Aggregate formation and the structure of the aggregates of disulfide-reduced proteins were investigated using alpha-lactalbumin and lysozyme as model proteins. First, reducing conditions were adjusted so that only one of the four disulfide bonds present in each native protein was cleaved. These three-disulfide (3SS) proteins are known to adopt almost native conformations, yet formed precipitates with a basic peptide, lactoferricin, and heparin and heparin fragment, respectively, at concentrations at which native proteins mixed with these compounds remained clear. The 3SS-lysozyme also formed precipitates in the absence of these ligands. Thus, subtle structural changes could lead to aggregation. Electron microscopy revealed fibrillar structures in the aggregates of extensively reduced proteins in the absence of ligands but not in their presence, which shows that the reduction of disulfide bonds suffices for fibril formation and that ligands inhibit fibril formation.

Hydrophobicity and flexibility of alpha A- and alpha B-crystallin are different

Since the discovery that the lens protein alpha-crystallin is also found in non-lenticular tissues and can function as a chaperone, relatively little attention has been paid to differences in properties between alpha A- and alpha B-crystallin, which form mixed aggregates in the lens but have so far never been found together in other tissues. In this study hydrophobicity and flexibility, properties that are thought to be relevant for chaperone function, are compared for alpha A- and alpha B-crystallin. Hydrophobicity was monitored from sodium dodecylsulphate polyacrylamide gel electrophoresis in the absence and presence of (methyl-substituted) ureas. Flexibilities were calculated from primary structures. Based on literature data also some other properties are compared. The results indicate significant difference in hydrophobicity profile, flexibility of the terminal parts and stability of alpha A- and alpha B-crystallin.

Contribution of disulfide bonds to stability of the folding intermediate of alpha-lactalbumin

The secondary structure formed in disulfide reduced alpha-lactalbumin is investigated by CD spectrum and is compared with that of the folding intermediate of the disulfide intact protein. The peptide backbone structure of the reduced protein depends strongly on salt concentration in contrast to that of the intermediate. It is close to a random coil in the absence of salt, but it is almost the same as that of the intermediate at a high concentration of salt. The secondary structures of both the proteins undergo broad unfolding transitions when temperature is raised or when urea is added. The secondary structure of the reduced protein is less stable against both heat and urea. These results show that the disulfide bonds are not a determinant of the secondary structure formed at an early stage of folding, and they stabilize the secondary structure of the folding intermediate.

Oxidation-reduction potential studies: a new method in pharmacology principles, materials, and methods

Oxidation-reduction (redox) potential measurement is not used in pharmacology at the present time. However, it represents a physicochemical parameter that may be as important as the other currently used physicochemical parameters, such as pH and pKa. Redox potential variations include conformational modifications that may influence bioavailability of drugs. We report here an original and convenient equilibrium method to determine this potential in biological fluids, especially in blood.

Evidence for interaction of substrate analogs with chicken eggwhite lysozyme after exhaustive reduction of disulfide bonds

In a study of factors that influence the remaining secondary structure of reduced chicken eggwhite lysozyme, N-acetyl-D-glucosamine (NAG) and N,N'-diacetylchitobiose (di-NAG) were found to alter the circular dichroic (CD) spectrum of the reduced protein and its carboxymethyl derivative (Cml). Thus, negative ellipticities in the far u.v. were greater in the presence of the analogs, with NAG being the more effective. For Cml, curve fitting analysis of the CD data indicated an increased helical content in the presence of NAG by an average of 3% of the chain length, while beta-structure decreased by an equivalent amount. Other compounds structurally related to NAG produced no similar effects on the CD spectrum of Cml, nor were comparable effects of NAG in evidence on the Cm reduced derivatives of ribonuclease, chymotrypsin, wheat germ agglutinin, or alpha-lactalbumin. The effect therefore appears specific between NAG and Cml. Conversion of the tryptophan residue at Position 62 of Cml to the oxindolealanyl derivative prevented these effects of NAG, and this residue may therefore participate in the interaction. During a 4-day incubation at room temperature, the analog preserved the CD spectrum of Cml as well as its concentration. This effect was nearly specific when compared with other Cm reduced proteins and with other carbohydrates. Only one, N-acetyl mannosamine, was effective in preserving the concentration of Cml, but not the CD spectrum. Since D-glucosamine was entirely without effect on either the CD spectrum of Cml or on its change during incubation, the acetyl group appears essential for the NAG-Cml interaction. The specificity between NAG and Cml is tentatively accounted for in terms of interactions with the primary structure, rather than with the remaining secondary structure.(ABSTRACT TRUNCATED AT 250 WORDS)