SVS II--an androgen-dependent actin-binding glycoprotein in rat semen

Rat seminal vesicles and the lateral prostate secrete a glycoprotein designated as SVS II in an androgen-dependent manner. SVS II, which has a M(r) of 49,000 and a pI of 10.5, is an actin-binding protein. G- and F-actins cosediment with SVS II at a ratio of 2:1 (actin:SVS II). SVS II affects the kinetics of actin polymerization in the same way as do barbed end capping proteins. Interaction with actin is specific for the skeletal and cardiac muscle isoforms and there is no corresponding interaction with cytoplasmic actins. The binding site is close to the C-terminus of actin. Monospecific polyclonal antibodies directed against the N-terminus of actin cross-react with SVS II, but there is no cross-reaction by a monoclonal antibody directed against a C-terminal epitope on actin. Recent sequence analysis of SVS II shows a sequence of about 14 residues that is repeated 13 times between residues 86 and 298. The consensus sequence based on these repeats is homologous to residues 10 to 25 of actin; this may account for the immunological cross-reactivity. Like actin, SVS II binds and inhibits the activity of DNase I, but SVS II has no effect on the ATPase activity of myosin subfragment 1. Thus, SVS II is an actin-binding protein which retains some properties of actin itself.