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 mai ntaining transparency and its function in other tissues under both nor mal and pathological conditions. Progress toward a unified consensus c oncerning the tertiary and quaternary structures of alpha-crystallin d epends, in part, on an accurate estimation of its secondary structure. For the first time, three algorithms, SELCON, K2D and CONTIN were use d to analyze far ultra-violet circular dichroism (UV-CD) spectra of bo vine lens alpha-crystallin to estimate the secondary structure and to determine the effects of temperature and concentration. Under all expe rimental conditions tested, the analyses show that alpha-crystallin co ntains 14% alpha-helix, 35% beta-sheet and the remainder, random coil and turns. The results suggest that alpha-crystallin is best classifie d as a mixed protein. In addition, increased temperature and concentra tion of alpha-crystallin result in increased alpha-helices with a comp ensatory decrease in beta-sheets. Such structural alterations in alpha -crystallin may be functionally important during terminal differentiat ion of the lens fiber cells that is accompanied by increased protein c oncentrations and its role as a chaperone-like protein. (C) 1997 Elsev ier Science B.V.