The chaperone alpha B-crystallin (alpha BC) is a member of the small heat shock protein family and its point or truncated mutants cause the muscular disorder alpha-crystallinopathy. The illness is histologically characterized by accumulation of protein aggregates in muscle cells. Expression of the myopathy-causing R120G mutant of alpha BC, harboring an arginine-to-glycine mutation at position 120, results in aggregate formation. We demonstrated that tethering alpha BC to the endoplasmic reticulum (ER) membrane represses the protein aggregation mediated by the R120G mutant. ER-anchored alpha BC decreased the amount of the R120G mutant through autophagic proteolysis. In contrast, knockdown of ATG5, an E3 ligase essential for autophagy, in ER-anchored alpha BC-transfected cells restored the quantity of the R120G mutant. In this context, aggregate formation was still suppressed, indicating that ER-anchored alpha BC profoundly constrains aggregation competency of the R120G mutant separately from downregulating the abundance of the mutant. We have proposed that protein aggregation is prevented by manipulation of the ER microenvironment with alpha BC, and have shed light on a novel aspect of the ER as a therapeutic target. (C) 2014 Elsevier Inc. All rights reserved.