The X-ray Crystal Structure of Human γS-crystallin C-terminal Domain*

γS-crystallin is a major human lens protein found in the outer region of the eye lens, where the refractive index is low. Because crystallins are not renewed they acquire post-translational modifications that may perturb stability and solubility. In common with other members of the βγ-crystallin superfamily, γS-crystallin comprises two similar β-sheet domains. The crystal structure of the C-terminal domain of human γS-crystallin has been solved at 2.4 Å resolution. The structure shows that in thein vitro expressed protein, the buried cysteines remain reduced. The backbone conformation of the “tyrosine corner” differs from that of other βγ-crystallins because of deviation from the consensus sequence. The two C-terminal domains in the asymmetric unit are organized about a slightly distorted 2-fold axis to form a dimer with similar geometry to full-length two-domain family members. Two glutamines found in lattice contacts may be important for short range interactions in the lens. An asparagine known to be deamidated in human cataract is located in a highly ordered structural region.

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