The native oligomeric organization of alpha-crystallin, is it necessary for its chaperone function?

Citraconylation of all the lysine residues of alpha B and alpha A disrupts the native oligomeric state of these proteins. For alpha B, the oligomerization is concentration dependent with monomers and dimers formed at low protein concentration (similar to0.01 mg ml(-1)). For concentration higher than 0.5 mg ml(-1) tetramers are the major species. Citraconylated alpha A crystallin is mostly tetrameric at any concentration. Citraconylation had a major effect on the secondary structure of alpha B which was reflected by a significant loss of beta-sheet structure. On the other hand, the secondary structure of alpha A crystallin was not significantly effected by this chemical modification. The chaperone properties of both modified proteins were the same as the native proteins when apo alpha-lactalbumin and malate dehydrogenase were used as target proteins. The data suggest that the native oligomeric state of alpha-crystallin may not be essential for its ability to suppress non-specific aggregation. (C) 2004 Elsevier Ltd. All rights reserved.