| Symbol: | CH |
| Calponin Homology Domain | |
| Pfam: | PF00307 |
| Pfam Clan: | CL0188 |
| Interpro: | IPR001715 |
| calponin 1, basic, smooth muscle | |
| Caption: | Solution structure of the CH domain of human Calponin 1. Rainbow colored cartoon (N-terminus = blue, C-terminus = red).[1] |
| Hgncid: | 2155 |
| Symbol: | CNN1 |
| Entrezgene: | 1264 |
| Omim: | 600806 |
| Refseq: | NM_001299 |
| Uniprot: | P51911 |
| Pdb: | 1WYP |
| Chromosome: | 19 |
| Arm: | p |
| Band: | 13.2-13.1 |
| calponin 2 | |
| Hgncid: | 2156 |
| Symbol: | CNN2 |
| Entrezgene: | 1265 |
| Omim: | 602373 |
| Refseq: | NM_004368 |
| Uniprot: | Q99439 |
| Chromosome: | 19 |
| Arm: | p |
| Band: | 13.3 |
| calponin 3, acidic | |
| Hgncid: | 2157 |
| Symbol: | CNN3 |
| Entrezgene: | 1266 |
| Omim: | 602374 |
| Refseq: | NM_001839 |
| Uniprot: | Q6FHA7 |
| Chromosome: | 1 |
| Band: | p22 |
| Locussupplementarydata: | -p21 |
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.[2] 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.[3]