Deamidation of Asn-143 of gammaS crystallin from protein aggregates of the human lens

Abstract

Purpose. Determine if gammaS crystallin is preferentially deamidated in the high molecular weight aggregate fraction of old human lenses. Methods. The high molecular weight aggregate and lower molecular weight fractions were prepared from water soluble proteins of old human lenses. Synthetic peptides corresponding to expected amidated and deamidated tryptic fragments of gammaS crystallin, together with reverse phase chromatography, were used to resolve and quantitate possible deamidation of glutamine-92, glutamine-96 and asparagine-143 from this protein. Results. Analyses of the high molecular weight aggregate from lenses of different ages consistently demonstrated deamidation of asparagine-143, with no deamidation of glutamine-92 or glutamine-96, while analyses of the lower molecular weight fraction from the same lenses showed no detectable deamidation of any of these three residues. Conclusions. Preferential deamidation of asparagine-143 of gammaS crystallin is present in the high molecular weight fraction of human lenses, consistent with the possibility that modification of this residue may play a role in the aggregation process occurring in vivo.