Beta crystallin is one of the eye lens proteins involved in cataract, a leading cause of blindness. The clouding of the eye in cataract depends on the strength of attractions and repulsions between its constituent proteins. This work studies forces between beta crystallins, to help quantitatively understand how those forces might be related to eye lens transparency. Bovine beta crystallin fractions were isolated using size-exclusion chromatography of 1-2 week old calf lens cortical homogenates, and studied using static and quasielastic light scattering at 633 nm wavelength, up to concentrations of 250 milligrams/milliter (mg/ml). These measurements yield excess Rayleigh ratios, or absolute cross sections for light scattering, and corresponding collective diffusion coefficients. For higher beta crystallin molecular weight fractions averaging 7x104 grams/mole, as measured by light scattering at low concentration, high concentration Rayleigh ratios plateau in the vicinity of 200 to 250 mg/ml, at close to 1.5 x 10-3 inverse centimeters. Collective diffusion coefficients are approximately constant at 5.5 x 10-7 cm2/sec over an extended concentration range, before decreasing at the highest concentrations.. We find that the Carnahan-Starling equation of state provides a useful approximation to the observed Rayleigh ratios within this concentration range. Thus the observed dependence of the Rayleigh ratios on concentration is approximately consistent with the influence of repulsive, hard-core interactions between beta crystallins.

Light scattering from concentrated eye lens beta crystallin solutions

250th National Meeting (2015)

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