Roles of protein deamidation in molecular and cellular aging.

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Deamidation of Asn residue is a chemical posttranslational alteration of the protein. it is now appreciated that deamidation would occur on most proteins in a time-dependent manner under physiological conditions. The purpose of this study was to elucidate roles and effects of deamidation in cellular aging as the molecular clock. We analyzed the amino acid residues of red cell membrane proteins, protein 4.1 and ankyrin, on which deamidation occurred and examined the functions of the deamidated proteins which was generated by site-directed mutagenesis. Mass spectrometry and amino acid analysis of the proteolytic peptides derived from protein 4.1 revealed that deamidation occurred at Asn502 and Asn478. We demonstrated that deamidation of Asn502 occurs very slowly during red cell aging with the change of apparent molecular mass. This was confirmed by converting a congenor of protein 4.1 to a deamidated form by mutagenesis. Changes of trypsin-sensitive sites within the polypeptide, particularly in the domains neighboring the deamidation sites, were observed, indicating a structural alteration of protein 4.1 molecule by deamidation. However, on significant differences was observed in the function of the protein 4.1 with or without Asn502 deamidation determined by binding to the red cell membranes which had been depleted of skeletal proteins. We also observed that the 2nd and 8th Asn-Gly sequence within the ANK repeat structure of the N-terminal 89-kDa domain of ankyrin were accessible to deamidation.