A 36 kDa monomeric protein and its complex with a 10 kDa protein both isolated from bovine aorta are calpactin-like proteins that differ in their Ca2+-dependent calmodulin-binding and actin-severing properties.

Interaction of plasma membrane with the cytoskeleton involves a large number of proteins, among them a 36 kDa protein that was found to be involved in the interaction with actin filaments. We have isolated a 36 kDa protein from bovine aorta as a monomer and in a complex with a 10 kDa protein. Partial amino acid sequence determinations show that the 36 kDa and 10 kDa proteins isolated from bovine aorta are analogous to or identical with corresponding proteins purified from bovine intestine already described by Kristensen, Saris, Hunter, Hicks, Noonan, Glenney & Tack [(1986) Biochemistry 25, 4497-4503]. We report here that the association of the 10 kDa protein with the 36 kDa protein confers specific calmodulin-binding and actin-severing properties on the complex that are not possessed by the 36 kDa monomer alone. These findings suggest that the protein complex could be involved in thin-filament-related structures or could modulate some Ca2+-regulated events mediated by calmodulin.