Identification and properties of anti-chaperone-like peptides derived from oxidized bovine lens betaL-crystallins

Thermal aggregation of betaL-crystallin was higher in the presence of peptide fragments generated from oxidized and trypsin-digested betaL-crystallin compared with thermal aggregation of the control proteins without oxidized betaL-crystallin fragments. Increased aggregation of betaL-crystallin was also observed despite the presence of alpha-crystallin (which has anti-aggregating properties) in the system. Self-aggregation of the oxidized betaL-crystallin fragments per se was not observed under the experimental conditions. Reverse-phase HPLC analysis of the precipitate obtained after heating a mixture of betaL-crystallin and oxidized betaL-crystallin fragments revealed that more than one peptide co-precipitates with betaL-crystallin. Electrospray mass spectrometry analysis of the peptides revealed that the molecular weight(s) of the peptides ranged from 1400-1800. Tandem mass spectrometry and a data base search revealed that two of the peptides originated from betaA4-crystallin (LTIFEQENFLGR, residues 121-132) and betaB3-crystallin (AINGTWVGYEFPGYR, residues 153-167) respectively. Oxidized synthetic peptides representing the same sequence were also found to enhance the aggregation of betaL-crystallin in a manner similar to oxidized lens betaL-crystallin peptides. These data suggest that the polypeptides generated after oxidation and proteolysis of betaL-crystallins interact with denaturing proteins and facilitate their aggregation and light scattering, thus behaving like anti-chaperones.