Deamidation of alpha-A crystallin from nuclei of cataractous and normal human lenses.

PURPOSE: To quantitate the extent of deamidation of asparagine-101, glutamine-50, and glutamine-6 of alpha-A crystallin in the nucleus from human cataractous and normal lenses.
METHODS: Reverse phase chromatography was used to prepare alpha-A crystallin from total proteins of the nucleus from cataractous and age-matched normal human lenses. Synthetic peptides were made corresponding to the expected amidated and deamidated tryptic fragments containing asparagine-101, glutamine-50, and glutamine-6. The peptides were used to identify and quantitate amidated and deamidated forms of tryptic fragments from alpha-A crystallin eluting from a reverse phase column.
RESULTS: Significant amounts of deamidation of asparagine-101 and glutamine-50, but not glutamine-6, were present in alpha-A crystallin from nuclear sections of both cataractous and age-matched normal lenses. Quantitative analysis of tryptic peptides containing these residues indicated no statistical difference in deamidation in cataractous versus normal lenses.
CONCLUSIONS: There was no significant difference in the extent of deamidation of asparagine-101, glutamine-50, and glutamine-6 for alpha-A crystallin, purified from the nucleus of cataractous versus age-matched normal lenses. These results strongly suggest that deamidation of these residues does not play a role in the biogenesis of human nuclear cataract.