A novel nonmuscle alpha-actinin. Purification and characterization of chicken lung alpha-actinin

Two distinct alpha-actinin-like proteins were detected in chicken lung extract by immunoblot analysis with monoclonal antibodies against alpha-actinin. The mobilities of these proteins on SDS-polyacrylamide gel electrophoresis are very close (approximately 100 kDa). On SDS-polyacrylamide gel electrophoresis in the presence of 6 M urea, however, one of the proteins migrates at 115 kDa and is clearly separated from the other protein (105 kDa). The 115-kDa protein was purified and shown to have at least three unique amino acid sequences which were not detected in other kinds of alpha-actinins: one locates at the extreme NH2-terminal region, and the others locate at the COOH-terminal half region. Immunoblot and proteolytic cleavage analyses revealed that the 115-kDa protein has structural divergence at the COOH-terminal region that includes Ca(2+)-binding EF-hand motifs. Falling-ball viscometric studies showed that although the 115-kDa protein-induced gelation of F-actin is sensitive to Ca2+, the gelation activity of the 115-kDa protein is much higher than that of Ca(2+)-insensitive gizzard alpha-actinin regardless of Ca2+. This indicates that the 115-kDa protein is distinct from other nonmuscle alpha-actinins by its Ca2+ sensitivity.