The molecular structure and stability of the eye lens: X-ray analysis of γ-crystallin II

The three-dimensional structure of the eye lens protein, bovine γ-crystallin II, has been determined at 2.6 Å resolution. The protein has a two domain β-structure, folded into four remarkably similar ‘Greek key’ motifs, and shows the highest internal symmetry of any protein studied by X-ray analysis. Although the symmetrical structure seems very stable, the arrangement of the sulphydryl groups would allow intramolecular cross-linking leading to possible destabilization, and intermodular cross-linking leading to aggregation, both of which may be important in cataract formation.