Post-Translational Modifications in the Nuclear Region of Young, Aged, and Cataract Human Lenses

The urea-soluble proteins from the nucleus of two young, two aged, and two early-stage nuclear cataract
lenses were subjected to tryptic digestion and analysis by 2D LC−MS/MS. Several novel post-translational modifications were identified. Deamidation was, by far, the most common modification.
A number of differences were found in cataract compared to normal lenses, most notably an increase
in the number of oxidized tryptophan residues. Semiquantitative analysis revealed that there appeared
to be a trend toward increased levels of deamidation with age; however, there was no apparent increase
upon the onset of nuclear cataract. This is in contrast to Trp oxidation, where an increase in the extent
of modification was apparent in cataract lenses when compared to aged normal lenses. These findings
suggest Trp oxidation may be involved in nuclear cataract development.
Keywords: post-translational modification • 2D LC−MS/MS • cataract • human lens • tryptophan • oxidation