STRUCTURE OF THE BOVINE EYE LENS PROTEIN GAMMA-B(GAMMA-II)-CRYSTALLINAT 1.47 ANGSTROM

The molecular structure of calf gammaB-crystallin (previously called g ammaII), a lens-specific protein, has been refined to a crystallograph ic R factor of 18.1% for all reflection data, between 8.0 and 1.47 ang strom, 25 959 hkl measured at 293 (1) K. 230 water molecules have been defined by difference Fourier techniques and included in a restrained least-squares refinement. Difference Fourier maps clearly indicated t he presence of multiple sites for the sulfur atoms of Cys 18 and Cys 2 2 which were therefore given coupled second-site occupancies during th e refinement. The sulfur atom in the major position of Cys 22 is in th e reduced state. Either of the Cys 18 sites can form a high-energy dis ulfide bridge with the minor position of Cys 22. The position of the c arboxy terminus and many other surface side chains have been further d efined including the RGD signal peptide. The hydration of the backbone and the interdomain region has been analysed. 27 water molecules make extensive contacts to a single protein molecule and thus contribute t o its stability.