Increased deamidation of asparagine during human senile cataractogenesis

To identify and quantitate deamidation of a specific asparagine residue of gammaS-crystallin that preferentially undergoes deamidation during the process of human senile cataractogenesis.

Reverse phase chromatography, together with synthetic peptide standards, was used to resolve the amidated and deamidated forms of asparagine-143 in the gammaS-crystallin sequence 131-145 from total tryptic digests of the central, nuclear region of human cataractous and normal lenses. Identities of the resolved peptides co-eluting with synthetic peptide standards were confirmed by mass spectral analysis. The synthetic peptide standards were also used to quantitate the amount of deamidation occurring in individual cataractous and normal lenses.

In all lenses analyzed, there was greater deamidation of asparagine-143 in cataractous lenses, as compared with age-matched normal lenses.

The results demonstrate, for the first time, that increased deamidation of a specific asparagine residue is present in proteins from the human cataractous lens.