αB-Crystallin in Skeletal Muscle: Purification and Localization1

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 (65% 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 alpha B-crystallin with the two proteins on immunoblotting. alpha B-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 alpha B-crystallin. Immunoblotting confirmed that most of the alpha B-crystallin was solubilized, though some was tightly bound to myofibrils. This bound portion was localized in Z-bands of isolated myofibrils by immunocytochemical light and electron microscopy. Muscle alpha B-crystallin is tentatively proposed to be a myofibril-stabilizing protein, based upon its extraction characteristics, localization, and amino acid sequence.