Calponin

Calponin Homology Domain
CH domain from H.Sapiends Calponin 1. PDB 1wyp
Identifiers
Symbol	CH
Pfam	PF00307
Pfam clan	CL0188
InterPro	IPR001715
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

calponin 1, basic, smooth muscle
Solution structure of the CH domain of human Calponin 1. Rainbow colored cartoon (N-terminus = blue, C-terminus = red).
Identifiers
Symbol	CNN1
Entrez	1264
HUGO	2155
OMIM	600806
PDB	1WYP
RefSeq	NM_001299
UniProt	P51911
Other data
Locus	Chr. 19 p13.2-13.1

Calponin is a calcium binding protein. Calponin tonically inhibits the ATPase activity of myosin in smooth muscle. Phosphorylation of calponin by a protein kinase, which is dependent upon calcium binding to calmodulin, releases the calponin's inhibition of the smooth muscle ATPase.

Calponin is mainly made up of α-helices with hydrogen bond turns. It is a binding protein and is made up of three domains. These domains in order of appearance are Calponin Homology (CH), regulatory domain (RD), and Click-23, domain that contains the calponin repeats. At the CH domain calponin binds to α-actin and filamin and binds to actin within the RD domain. Calmodulin, when activated by calcium may bind weakly to the CH domain and inhibit calponin binding with α-actin. Calponin is responsible for binding many actin binding proteins, phospholipids, and regulates the actin/myosin interaction. Calponin is also thought to negatively affect the bone making process due to being expressed in high amounts in osteoblasts.