Post-translational modification of alphaB-crystallin of normal human lens.

The current study reports several post-translational modifications of alphaB-crystallin in normal human lenses. The isoforms of post-translational modified alphaB-crystallin were isolated from the normal human lenses of >70-age group by ion exchange chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isoform modifications were determined in detail by fast atom bombardment mass spectroscopy and amino acid sequence analysis. As the criterion of non-modified alphaB-crystallin, alphaB-crystallin from 1-d-old infant lenses were used. The modifications found in this study involve oxidation of the N-terminal methionine-1 residue, phosphorylation of the serine-59 residue, and truncation of four amino acids from the C-terminal position of the crystallin. The oxidation of methionine-1 was found in the early stage of human life in 1-d-old lens, although other modification of alphaB-crystallin were usually only found in old lenses (>70-age group).