The cardiomyopathy and lens cataract mutation in αB-crystallin alters its protein structure, chaperone activity, and interaction with intermediate filaments in vitro

Desmin-related myopathy and cataract are both caused by the R120G mutation in alpha B-crystallin, Desmin-related myopathy is one of several diseases characterized by the coaggregation of intermediate filaments with alpha B-crystallin, and it identifies intermediate filaments as important physiological substrates for alpha B-crystallin, Using recombinant human alpha B-crystallin, the effects of the disease-causing mutation R120G upon the structure and the chaperone activities of alpha B-crystallin are reported, The secondary, tertiary, and quaternary structural features of alpha B-crystallin are all altered by the mutation as deduced by near- and far-UV circular dichroism spectroscopy, size exclusion chromatography, and chymotryptic digestion assays. The R120G alpha B-crystallin is also less stable than wild type alpha B-crystallin to heat-induced denaturation, These structural changes coincide with a significant reduction in the in vitro chaperone activity of the mutant alpha B-crystallin protein, as assessed by temperature-induced protein aggregation assays. The mutation also significantly altered the interaction of alpha B-crystallin with intermediate filaments. It abolished the ability of alpha B-crystallin to prevent those filament filament interactions required to in duce gel formation while increasing alpha B-crystallin binding to assembled intermediate filaments. These activities are closely correlated to the observed disease pathologies characterized by filament aggregation accompanied by alpha B-crystallin binding. These studies provide important insight into the mechanism of alpha B-crystallin-induced aggregation of intermediate filaments that causes disease.