The cardiomyopathy and lens cataract mutation in alpha B-crystallin altersits 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 c haracterized by the coaggregation of intermediate filaments with alpha B-cr ystallin, and it identifies intermediate filaments as important physiologic al substrates for alpha B-crystallin, Using recombinant human alpha B-cryst allin, the effects of the disease-causing mutation R120G upon the structure and the chaperone activities of alpha B-crystallin are reported, The secon dary, tertiary, and quaternary structural features of alpha B-crystallin ar e all altered by the mutation as deduced by near- and far-UV circular dichr oism spectroscopy, size exclusion chromatography, and chymotryptic digestio n assays. The R120G alpha B-crystallin is also less stable than wild type a lpha B-crystallin to heat-induced denaturation, These structural changes co incide with a significant reduction in the in vitro chaperone activity of t he mutant alpha B-crystallin protein, as assessed by temperature-induced pr otein aggregation assays. The mutation also significantly altered the inter action of alpha B-crystallin with intermediate filaments. It abolished the ability of alpha B-crystallin to prevent those filament filament interactio ns required to in duce gel formation while increasing alpha B-crystallin bi nding to assembled intermediate filaments. These activities are closely cor related to the observed disease pathologies characterized by filament aggre gation accompanied by alpha B-crystallin binding. These studies provide imp ortant insight into the mechanism of alpha B-crystallin-induced aggregation of intermediate filaments that causes disease.