Effects of temperature and concentration on bovine lens alpha-crystallin secondary structure: a circular dichroism spectroscopic study.

Elucidation of the structure of alpha-crystallin, the major protein in all vertebrate lenses, is important for understanding its role in maintaining transparency and its function in other tissues under both normal and pathological conditions. Progress toward a unified consensus concerning the tertiary and quaternary structures of alpha-crystallin depends, in part, on an accurate estimation of its secondary structure. For the first time, three algorithms, SELCON, K2D and CONTIN were used to analyze far ultra-violet circular dichroism (UV-CD) spectra of bovine lens alpha-crystallin to estimate the secondary structure and to determine the effects of temperature and concentration. Under all experimental conditions tested, the analyses show that alpha-crystallin contains 14% alpha-helix, 35% beta-sheet and the remainder, random coil and turns. The results suggest that alpha-crystallin is best classified as a mixed protein. In addition, increased temperature and concentration of alpha-crystallin result in increased alpha-helices with a compensatory decrease in beta-sheets. Such structural alterations in alpha-crystallin may be functionally important during terminal differentiation of the lens fiber cells that is accompanied by increased protein concentrations and its role as a chaperone-like protein.