Ischemia-induced association of the stress protein alpha B-crystallin with I-band portion of cardiac titin.

During ischemia the cardiac stress protein, alpha B-crystallin, was shown by immunoelectron microscopy to translocate to the N(2)-line area of myofibrillar I-bands of rat cardiomyocytes where alpha B-crystallin resisted extraction with 1 m NaSCN and 2 m urea as did titin. Actin became completely extracted under these conditions, indicating association of alpha B-crystallin with titin the only remaining non-actin cytoskeletal component of I-bands outside Z-disks. Titin, extracted from ischemic pig myocardium, was shown to copurify with alpha B-crystallin. Further evidence for binding of alpha B-crystallin to titin was obtained by dot-blot assays in which biotinylated alpha B-crystallin was demonstrated to bind to the titin-enriched fraction immobilized on nitrocellulose. Binding of alpha B-crystallin to titin during cardiac ischemia could serve to stabilize titin against denaturation and might provide an endogenous mechanism to delay ischemic damage of this important elastic component of myofibrils. Copyright 2002 Academic Press.