Abstract
Abstract: :
Purpose:To study whether X-ray scattering data, reflecting the liquid structure of high concentration α and γ B crystallin mixtures, can be reproduced by Monte Carlo simulation of particles interacting via simple, appropriate model potentials. Methods:Model γ B-γ B interactions combined hard-core repulsion of effective spheres with an attractive Yukawa potential . α-α and α-γ B interactions were represented by hard-core repulsion alone. The Yukawa range and depth were chosen using the known critical volume fraction and critical temperature for γ B-crystallin. Effective sphere sizes were chosen using the known molecular volume of γ B, and the radius of gyration observed by X-ray scattering for α. For X-ray scattering, calf lens proteins were isolated using size-exclusion and ion-exchange chromatography, concentrated by ultrafiltration, and analyzed in solutions containing 0.1 M sodium phosphate buffer, pH 7.1, with 20mM dithiothreitol. The X-ray scattering intensity, I(q), as a function of wavevector, q, was measured in the range 0.04 < q < 6 nm-1, using Beamline 8-ID at the Advanced Photon Source. Results:We find nearly quantitative agreement between the simulated I(q) and the measured I(q), at a total protein concentration of 260 mg/ml, for α-crystallin relative proportions ranging from 0 to 1. Refinements to incorporate more realistic γ B-crystallin shape may be needed. Conclusion:Simple model potentials such as these can provide useful starting points for understanding the liquid structure of lens crystallin mixtures, at concentrations comparable to those in the eye lens.
Keywords: 378 crystallins