The X-ray crystal structure of human gamma S-crystallin C-terminal domain.

Andrew G Purkiss,Christine Slingsby,Julia M Goodfellow,Orval A Bateman,Nicolette H Lubsen

doi:10.1074/jbc.m110083200

Abstract

gammaS-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 betagamma-crystallin superfamily, gammaS-crystallin comprises two similar beta-sheet domains. The crystal structure of the C-terminal domain of human gammaS-crystallin has been solved at 2.4 A resolution. The structure shows that in the in vitro expressed protein, the buried cysteines remain reduced. The backbone conformation of the "tyrosine corner" differs from that of other betagamma-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.

Highlights

The lens crystallins are protein molecules that need to last a lifetime, because they are found in cells that have no protein synthetic or degradation machinery (1)
␥S-crystallin is a major human lens protein found in the outer region of the eye lens, where the refractive index is low
As a first step toward providing detailed molecular information on a major human lens crystallin involved in cataract, we have solved the x-ray crystal structure of the C-terminal domain from human ␥S-crystallin

Summary

The crystallins are a well studied family of proteins for which

The atomic coordinates and structure factors (code 1ha4) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/). The N- and C-terminal domains pair about a similar pseudo-2-fold axis, with the domains in monomeric ␥-crystallins being covalently connected, whereas domain swapping can lead to dimerization in ␤-crystallins (8). Several x-ray structures of ␥A-F crystallins are known, and they all show very similar two-domain pairing about a hydrophobic interface that contributes toward stability (14 –17). For ␥S-crystallin, only the C-terminal domain of the bovine protein has been solved by x-ray crystallography (25), showing how two domains self-associate to form a dimer in an analogous way to that of the native two-domain ␥-crystallins, This paper is available on line at http://www.jbc.org. We show that the C-terminal domains of human ␥S-crystallin pair about a slightly distorted 2-fold axis to form a dimer with both tyrosine corners in a nonstandard conformation

EXPERIMENTAL PROCEDURES

Solvent content

RESULTS

Surface area buried