Crystal structure of calf eye lens gamma-crystallin IIIb at 2.5 A resolution: its relation to function.

The crystal structure of gamma-crystallin IIIb (gamma C) from calf eye lens has been refined at 2.5 A resolution. The molecule of about 21 kDa consists of two similar domains. Each domain is composed of two motifs with the 'Greek key' topology which form a pair of four-stranded beta-sheets with an antiparallel packing. The molecule has three hydrophobic cores: one within each domain and one between them. Six of the eight functionally important cysteines are located within the N-domain, and only two in the C-domain. Several large clusters of charged residues are at the surface of the molecule. Surface residues Val 101, Met 103 and Leu 155 are important for packing of molecules in crystal medium and possibly in the lens. Features of the gamma-crystallin IIIb molecule which may be related to its function in the vertebrate eye lens are briefly discussed. An attempt has been made to correlate molecular characteristics with some general properties of the eye lens such as high density and refractive index gradients and strong stability of the lens during an organism's lifetime.

Molecular cartography of proteins: surface relief analysis of the calf eye lens protein gamma-crystallin.

Methods of calculating the protein molecular surface and different map representations are described. The maps are obtained by projection of the space-filling molecular model on the surface of the ellipsoid of inertia. A new approach to surface analysis is proposed which is based on the use of three general maps: an identification map with all residues outlined, a surface relief map and a coloured map with a specific colour for each of the surface atoms. Superposition of these maps greatly simplifies molecular surface analysis. The usefulness of such an approach has been demonstrated by the study of the relief of the calf eye lens protein gamma-crystallin II. Protrusions of the relief have been shown to be occupied generally by charged residues, but in some cases by the hydrophobic ones. It is interesting to note that in crystal medium the protruding residues are involved, in the majority of cases, in intermolecular contacts. The protruding regions have been found to be pseudosymmetrical to each other in accordance with the two-fold rotation axis of the molecule. However, the colours of these regions, i.e. the atoms of the corresponding side chains, differ greatly.