Molecular interactions in the eye lens.

Introduction The lens is a cellular structure formed from elongated fibre cells aligning into concentric layers that stack together with the organization of a uni-axial crystal 111. Within the fibre cells, where protein turnover is low, protein components are packed together [2-41 with short-range order [S]. The high protein concentration is important both for refraction and transparency. Globular proteins fold compactly into domains with the exclusion of water [6]. The index of refraction of a concentrated protein solution is therefore higher than water, and the short-range correlation in protein positions reduces light scattering, ensuring that the medium is transparent 171. Any mechanism that produces spatial fluctuations in the index of refraction, such as protein aggregation or phase separation, will result in turbidity [ X I . Knowledge of the molecular basis of cataract is dependent on an understanding of the forces that control the distribution and spacing of lens proteins. Although lenses are transparent as a result of uniformity of refractive index on the scale of the wavelength of light, the constituent structural proteins are extremely diverse. All vertebrate lenses comprise members from two superfamilies, aand /?, y-crystallins. Whereas a-crystallins are derived from two genes ( a A , aB), P,y-crystallins are encoded by at least thirteen genes (PBI, pB2, PB3,