Calponin is a smooth muscle-specific, actin-, tropomyosin- and calmodulin-binding protein believed to be involved in regulation or modulation of contraction [<cite idref="PUB00001664"/>]; interaction of the protein with actin inhibits actomyosin MgATPase activity. Multiple isoforms are found in smooth muscle [<cite idref="PUB00002836"/>]. Calponin is a basic protein of ~34 Kd [<cite idref="PUB00002979"/>]. The protein contains three repeats of a well-conserved 26-residue domain (see <db_xref db="INTERPRO" dbkey="IPR000557"/>).