Surface interactions of γ‐crystallins in the crystal medium in relation to their association in the eye lens

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Abstract
A comparative study of intermolecular interactions in crystals of two homologous low molecular weight proteins, γ‐II and γ‐IIIb crystallins, from calf eye lens was carried out. Crystal packings for these proteins are very different: intermolecular contact areas compose about 33% of the total accessible surface area of γ‐II as compared with 13% in γ‐III. Two key residues seem to be mainly responsible for the differences in protein association in the crystal medium. These are Ser 103 and Leu 155 in γ‐II, which are replaced by Met 103 and His 155 in γ‐IIIb. A similar substitution of these residues is observed in different gene products of γ‐crystallins from a number of vertebrates. This is consistent with the existence of a genetically controlled mechanism for determining intermolecular association of γ‐crystallins in the native medium of the lens.