The molecular refractive function of lens gamma crystallins

Monday, October 24, 2011 — Poster Session I
Noon – 2:00 p.m.	Natcher Conference Center	NIBIB	BIOINFO-20

Authors

• H Zhao
• PH Brown
• M Magone
• P Schuck

Abstract

Gamma crystallins are the major protein component in the nucleus of the eye lens. They exhibit extremely high solubility and thermodynamic stability to help prevent scattering of light and the formation of cataracts. However, functions beyond this structural role have remained mostly unclear. In the present work, we show that all lens gamma crystallins have evolved a significantly elevated molecular refractive index increment, which is far above those of most proteins, and above non-lens members of the beta-gamma crystallin family from different species. The same trait has evolved in parallel in crystallins of different phyla, including in the S-crystallins of cephalopods. A high refractive index increment can lower the crystallin concentration required to achieve a suitable refractive power of the lens, and thereby reduce the propensity of crystallins to aggregate and form cataract. To achieve a sufficiently high refractive index increment, a global shift in the amino acid composition is required, which can naturally explain the highly unusual amino acid composition of gamma crystallins and their functional homologues. This function provides a new perspective for interpreting their molecular structure.

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