Calponin
Encyclopedia
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.
. At the CH domain calponin binds to α-actin and filamin and binds to actin within the RD domain. Calponin does not bind to actin in the CH domain as generally described due to the fact that the CH domain is known to bind calcium to calmodulin which then inhibits actin binding. Calponin is responsible for binding many actin binding proteins, phospholipids, and regulates the actin/myosin interaction. Calponin is also thought to negatively effect the bone making process due to being expressed in high amounts in osteoblasts
.
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
binding protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
. Calponin tonically inhibits the ATPase activity of myosin in smooth muscle. Phosphorylation of calponin by a protein kinase
Kinase
In chemistry and biochemistry, a kinase is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates, a process referred to as phosphorylation. Kinases are part of the larger family of phosphotransferases...
, which is dependent upon calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
binding to calmodulin
Calmodulin
Calmodulin is a calcium-binding protein expressed in all eukaryotic cells...
, releases the calponin's inhibition of the smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
ATPase.
Sturcture and function
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 repeatsCalponin family repeat
In molecular biology, the calponin family repeat is a 26 amino acid protein domain. Calponin-1 contains three copies of this domain. This domain is also found in vertebrate smooth muscle protein , and a number of other proteins whose physiological role is not yet established, including Drosophila...
. At the CH domain calponin binds to α-actin and filamin and binds to actin within the RD domain. Calponin does not bind to actin in the CH domain as generally described due to the fact that the CH domain is known to bind calcium to calmodulin which then inhibits actin binding. Calponin is responsible for binding many actin binding proteins, phospholipids, and regulates the actin/myosin interaction. Calponin is also thought to negatively effect the bone making process due to being expressed in high amounts in osteoblasts
Osteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...
.