Purification, characterization, and partial sequence analysis of a new 25-kDa actin-binding protein from bovine aorta: a SM22 homolog.

We have purified a Ca(2+)-sensitive 25-kDa protein from bovine aorta. The 25-kDa protein remains associated with the membrane fraction in the presence of Ca2+ and is dissociated by EGTA. The purified protein binds directly to F-actin at a ratio of 1:6 actin monomers, with a binding constant of 7.0 x 10(5) M-1. The partial sequence analysis revealed a high homology to predicted protein derived from mRNA, named WS3-10 and chicken SM22 protein. Although chicken SM22 had not any interaction with contractile proteins or Ca2+, the bovine homolog clearly binds to F-actin and has Ca(2+)-binding domain in its primary structure.