α-Crystallin can function as a molecular chaperone

Abstract

The α-crystallins (αA and αB) are major lens structural proteins of the vertebrate eye that are related to the small heat shock protein family. In addition, crystallins (especially αB) are found in many cells and organs outside the lens, and αB is overexpressed in several neurological disorders and in cell lines under stress conditions. Here I show that α-crystallin can function as a molecular chaperone. Stoichiometric amounts of αA and αB suppress thermally induced aggregation of various enzymes. In particular, α-crystallin is very efficient in suppressing the thermally induced aggregation of β- and γ-crystallins, the two other major mammalian structural lens proteins. α-Crystallin was also effective in preventing aggregation and in refolding guanidine hydrochloride-denatured γ-crystallin, as judged by circular dichroism spectroscopy. My results thus indicate that α-crystallin refracts light and protects proteins from aggregation in the transparent eye lens and that in nonlens cells α-crystallin may have other functions in addition to its capacity to suppress aggregation of proteins.