Background: This study was designed to establish whether increased glycation of human crystallins could be related to an increased susceptibility to aggregation and insolubilization. The study was focused particularly on the glycation levels and composition of low-molecular-weight (LMW) peptides present in human cataractous lenses.
Methods: Lens crystallins from the water-soluble fraction were separated on a preparative scale by gel filtration. Each crystallin was purified and its glycation level evaluated as furosine content. The peptides were further purified by reverse-phase chromatography. The amino acid composition of each of these peptides was also determined by RP-HPLC using PITC pre-column derivatization.
Results: The high-molecular-weight (HMW), alpha L-crystallin and LMW crystallins from diabetic patients present high furosine content. LMW peptides were shown to constitute a heterogeneous population of three major peptides with a lysine content similar to that observed for native crystallins. These peptides were shown to present glycation levels 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.
Conclusions: LMW peptides are suggested to play a major role in protein aggregation and insolubilization, probably via a mechanism involving protein glycation. This process seems to be particularly relevant to diabetic cataract development.