DEAMIDATION AND DISULFIDE BONDING IN HUMAN LENS GAMMA-CRYSTALLINS

Detailed analysis of the three gamma-crystallins present in the water- soluble portion of human lenses, gamma S, gamma D and gamma C, has ide ntified disulfide bonding and deamidation as the major post-translatio nal modifications of these crystallins. Chromatographic and mass spect rometric techniques were used to isolate and identify water-soluble ga mma-crystallins from normal lenses, ages 32 week gestation, 0 day old, 4 day old, 19, 31, 45 and 55 year old. The amino acid sequences of th e gamma-crystallins were confirmed and/or corrected by mass spectromet ric analysis of peptides produced by enzymatic digestion or chemical f ragmentation of the isolated crystallins. The molecular weight of pept ides were also used to identify, locate and quantify modifications. Ea ch of the gamma-crystallins had two disulfide bonds as well as several deamidated glutamine and asparagine residues. The extent of disulfide bond formation and deamidation appeared to increase with the age of t he lens. This examination of normal human lens gamma-crystallins, the first detailed characterization of the gamma-crystallins, will provide a basis fbr comparison with modifications found in the water-insolubl e portion and in cataractous lenses. (C) 1998 Academic Press.