Calponin is a family of actin filament-associated proteins which regulate smooth muscle cell contraction. It is capable of binding to actin, calmodulin, troponin C and tropomyosin. Three isoforms of calponin exist: calponin h1 (CNN1) , calponin h2 (CNN2) and calponin 3 (CNN3). CNN1 is expressed in smooth muscle and tissues containing significant amounts of smooth muscle. Two isoforms of calponin exist whose molecular weights are 34kDa and 29kDa.