THE C-TERMINAL DOMAINS OF GAMMA-S-CRYSTALLIN PAIR ABOUT A DISTORTED TWOFOLD AXIS

The 2-domain gamma S-crystallin, a highly conserved early evolutionary off-shoot of the gamma-crystallin family, is located in the water-ric h region of eye lenses. The expressed C-terminal domain, gamma S-C, ha s been crystallized and the 2.56 Angstrom X-ray structure determined. There are two domains in the asymmetric unit which pair about a distor ted twofold axis. One of the domains has an altered conformation in a highly conserved region of the protein, the tyrosine corner. The disto rted gamma S-C dimer of domains is compared with the highly symmetrica l, equivalent recombinant dimer of C-terminal domains from gamma B-cry stallin. Sequence changes close to the interface, that distinguish gam ma S from the other gamma-crystallins, are examined in order to evalua te their role in symmetrical domain pairing.