In vivo carbamylation and acetylation of water‐soluble human lens αB‐crystallin lysine 92

Several post‐translational modifications of lysine residues of lens proteins have been implicated in cataractogenesis. In the present study, the molecular weight of an α‐crystallin isolated from the water‐soluble portion of a cataractous human eye lens indicated that it was a modified αB‐crystallin. Further analysis by mass spectrometry of tryptic digests of this modified protein showed that Lys 92 was modified and that the sample was structurally heterogeneous. Lys 92 was acetylated in one population and carbamylated in another. Although carbamylation of lens crystallins has been predicted, this is the first documentation of in vivo carbamylation of a specific site. These results are also the first documentation of in vivo lysine acetylation of αB‐crystallin. Both modifications alter the net charge on αB‐crystallin, a feature that may have significance to cataractogenesis.

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