EVIDENCE FOR THE PARTICIPATION OF ALPHA-B-CRYSTALLIN IN HUMAN AGE-RELATED NUCLEAR CATARACT

The aim of this study was to determine if the unusual coloured species characteristic of age-related nuclear cataract could be localised to specific residues of the crystallins. The insoluble, crosslinked and c oloured cataract protein fraction (CPF) was isolated from cataract hum an lenses. Using a combination of tryptic digestion, gel filtration an d multiple reversed phase high performance liquid chromatography (RP-H PLC), coloured peaks were isolated and subjected to amino acid sequenc e analysis. With these techniques, it was hoped to identify and locate the modified residues. Sequence information was obtained on 16,'colou red' peptides. Many of the peptides were found to be derived from alph a B-crystallin. When redundancies are taken into account, six distinct ive peptides were found to be derived from alpha B-cryslallin; one fro m beta B1-crystallin, two from beta A3/A1-crystallin and three from ga mma S-crystallin. Three sites of possible crystallin residue isomerisa tion to modification were detected in the alpha B- and beta A3/beta A1 -crystallins, including probable asp isomerisation at residues 25 and 36 in alpha B-crystallin. Since the CPF is unique to nuclear cataract lenses, these data suggest that alpha-crystallin, and alpha B-crystall in in particular, may be implicated in the cataract process. This find ing supports that of a recent study on cataract proteins using pronase digestion [Chen YC, Reid GE, Simpson RJ, Truscott RJW. Exp Eye Res 19 97;65:835.]. (C) 1998 Elsevier Science B.V. All rights reserved.