aB-Crystallin in Cardiac Tissue Association With Actin and Desmin Filaments

aB-Crystallin is a 20-kd peptide highly homologous to the small heat-shock proteins. This protein forms soluble homomultimeric complexes (M, 300-700 kd) and is very abundant in cardiac muscle cells. In vitro experiments (affinity column chromatography and binding studies with isolated proteins) have shown that aB-crystallin interacts directly with actin and, in particular, with desmin filaments. The immunocytochemical localization of aB-crystallin within the cardiomyocytes showed that the protein is distributed exclusively in the central region of the I bands (Z lines), where desmin is localized. In vitro studies have further shown that the binding affinity of aB-crystallin to actin and desmin filaments increases considerably at slightly acidic pH (6.5) or after a heat treatment (45C). Moreover, aB-crystallin was found to prevent effectively the tendency of actin filaments to form aggregates (i.e., paracrystals) at acidic pH. These in vitro data suggest a protective role of aB-crystallin during stress conditions such as ischemia of the heart. Crystallin could prevent the aggregation of filaments, which might occur during the acidification of the cytosol and lead eventually to irreversible structural damage. (Circulation Research 1992;71:288-294)