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Mutations in the human γD crystallin gene trigger cataract formation
By Bijal P. Trivedi

Researchers have determined that certain mutant forms of gD crystallin lower the solubility of the protein leading to spontaneous crystallization, which causes the human lens to develop cataracts.

The transparency of the eye's lens is maintained in large part by three proteins: a, b and gD crystallin. Researchers led by George Benedek, of the Massachusetts Institute of Technology, Cambridge, MA, have determined that in two mutants—R36S and R58H—the structure of the gD crystallin protein is modified in such a way that the protein is more susceptible to crystallization.

Based on X-rays showing the arrangement of the atoms within the gD crystallin protein, Benedek's team suggests that the structural changes in the R36S mutant are minute. However, these tiny structural alterations are able to modify the chemical properties of the mutant protein to make it less soluble. The results of this study appear in the current issue of Proceedings of the National Academy of Sciences.

Crystals have been found in the cataract of an individual carrying the R36S mutation. Based on their study, Benedek and colleagues predict that the aculeiform cataract, which has been linked to the R58H mutant of gD crystallin protein, is also due to the formation of crystals.

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Pande, A. et al. Crystal cataracts: Human genetic cataract caused by protein crystallization. Proc Natl Acad Sci USA 98, 6116-6120 (May 22, 2001).

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