CRYSTALLIN COMPOSITION OF HUMAN CATARACTOUS LENS MAY BE MODULATED BY PROTEIN GLYCATION

Background: This study was designed to establish whether increased gly cation of human crystallins could be related to an increased susceptib ility to aggregation and insolubilization. The study was focused parti cularly on the glycation levels and composition of low-molecular-weigh t (LMW) peptides present in human Methods: Lens crystallins from the w ater-soluble fraction were separated on a preparative scale by gel fil tration. Each crystallin was purified and its glycation level evaluate d as furosine content. The peptides were further purified by reverse-p hase chromatography. The amino acid composition of each of these pepti des was also determined by RP-HPLC using PITC pre-column derivatizatio n. Results: The high-molecular-weight (HMW), alpha(L)-crystallin and L MW crystallins from diabetic patients present high furosine content. L MW peptides were shown to constitute a heterogeneous population of thr ee major peptides with a lysine content similar to that observed for n ative crystallins. These peptides were shown to present glycation leve ls ten times higher than those observed for the crystallins. Glycated proteins from insoluble fraction were found to be mostly urea soluble and were present at higher concentration in diabetic cataracts. Conclu sions: LMW peptides are suggested to play a major role in protein aggr egation and insolubilization, probably via a mechanism involving prote in glycation. This process seems to be particularly relevant to diabet ic cataract development.