αB-Crystallin in Skeletal Muscle: Purification and Localization

Abstract

Atrophy of rat soleus muscles by hindlimb suspension is characterized by an early dramatic decrease in a soluble 22-kDa protein. The 22-kDa protein was purified from rat red skeletal muscle and rat lens by three different methods of chromatography. The partial amino acid sequence (66% of total amino acids) determined for muscle 22-kDa protein was identical with that of rat lens crystallin. The HPLC elution patterns of lysylendopeptidase fragments of 22-kDa protein from the two sources were identical. Polyclonal antibodies to rat muscle and bovine lens αB-crystallin with the two proteins on immunoblotting. αB-Crystallin protein was expressed and synthesized efficiently in slow skeletal muscle and poorly in fast muscle. Thus, the decreased 22-kDa protein of slow muscle in the suspension treatment was confirmed to be αB-crystallin. Immunoblotting confirmed that most of the αB-crystallin was solubilized, though some was tightly bound to myofibrils. This bound portion was localized in Z-bands of isolated myofibrils by immunocyto-chemical light and electron microscopy. Muscle αB-crystallin is tentatively proposed to be a myofibril-stabilizing protein, based upon its extraction characteristics, localization, and amino acid sequence.