CALPONIN

Calponin is a troponin-T like protein purified from chicken gizzard sm ooth muscle. It binds to actin, myosin, Ca2+-binding proteins and trop omyosin and inhibits the actomyosin ATPase as well as the movement of actin filaments over myosin in vitro. These properties have led to the proposal that calponin may be involved in the Ca2+-dependent regulati on of actin-myosin interaction and consequently of smooth muscle contr action. Calponin is localized in both the contractile;md the cytoskele tal parts of the smooth muscle cell and may have a structural function in smooth muscle cells. It may also regulate the pool of free actin a vailable for cytoskeleton organization. In vitro calponin function is modulated by its interaction with a Ca2+-binding protein and/or by its phosphorylation. This suggests that calponin may play an important ro le in signal transduction from the membrane receptor to the contractil e proteins in smooth muscle. Copyright (C) 1996 Elsevier Science Ltd