Human αB‐Crystallin suppresses the aggregation in vitro of partially folded intermediates of human γC‐, γD‐, and γS‐Crystallins

Abstract

α‐crystallin, a small heat shock protein chaperone, is one of the ubiquitous crystallins in the vertebrate lens, along with the ??‐crystallins. It is a polydisperse complex of ~ 800 kD consisting of two subunits (~20 kD) αA‐ and αB‐crystallin (αA‐ and αB‐crys). Its chaperone activity involves suppressing aggregation by binding aggregation‐prone species. Aggregates isolated from mature‐onset cataracts, the major cause of blindness worldwide, contain damaged and misfolded forms of ??‐crystallins. Human ?D‐ and ?C‐crystallin (H?D‐ and H?C‐crys) are stable, long‐lived ?‐crystallins in the lens nucleus, while ?S‐crystallin (H?S‐crys) is abundant in the lens cortex. All three ?‐crystallins can refold in vitro to their native state after unfolding in high concentrations of GdnHCl. Refolding unfolded H?C‐, H?D‐, or H?S‐crys to very low GdnHCl concentrations (< 1 M) resulted in partially folded intermediates partitioning between productive refolding and aggregation pathways. H?D‐, H?C‐ or H?S‐Crys protein was allowed to refold and aggregate in the presence of HαB‐Crys at different monomer‐to‐monomer ratios. H?D‐ and H?C‐Crys aggregation was suppressed to similar levels, whereas H?S‐Crys aggregation was not suppressed as well under identical conditions in assays measuring solution turbidity at 350 nm. These results provide a model for how α‐crystallin interacts with aggregation‐prone substrates in vivo