Activin A receptor, type I (ACVR1) is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

which in humans is encoded by the ''ACVR1''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

; it is also known as ALK-2 (activin receptor-like kinase-2). ACVR1 has been linked to the 2q23-24 region of the genome. This protein is important in the

bone morphogenic protein Bone morphogenetic proteins (BMPs) are a group of growth factors also known as cytokines and as metabologens. Professor Marshall Urist and Professor Hari Reddi discovered their ability to induce the formation of bone and cartilage, BMPs are now ...

(BMP) pathway that is responsible for the development and repair of the skeletal system. While knockout models with this gene are in progress, the ACVR1 gene has been connected to fibrodysplasia ossificans progressiva, an extremely rare progressive genetic disease characterized by

heterotopic ossification Heterotopic ossification (HO) is the process by which bone tissue forms Heterotopia (medicine), outside of the skeleton in muscles and soft tissue. Symptoms In traumatic heterotopic ossification (traumatic myositis ossificans), the patient may ...

of muscles, tendons, and ligaments. It is a bone morphogenetic protein receptor, type 1.

Function

Activin Activin and inhibin are two closely related protein complexes that have almost directly opposite biological effects. Identified in 1986, activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual c ...

s are dimeric growth and differentiation factors that belong to the transforming growth factor-beta (

TGF beta Transforming growth factor beta (TGF-β) is a multifunctional cytokine belonging to the Transforming growth factor beta family, transforming growth factor superfamily that includes three different mammalian isoforms (TGF-β 1 to 3, HUGO Gene Nomen ...

) superfamily of structurally related signaling proteins. Activins signal through a heteromeric complex of receptor

serine kinase A serine/threonine protein kinase () is a kinase enzyme, in particular a protein kinase, that phosphorylation, phosphorylates the hydroxyl, OH group of the amino acid, amino-acid residues serine or threonine, which have similar side chains. ...

s that include at least two type I ( I and IB) and two type II (II and IIB) receptors. These receptors are all

transmembrane protein A transmembrane protein is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequently un ...

s, composed of a ligand-binding extracellular domain with cysteine-rich region, a

transmembrane domain A transmembrane domain (TMD, TM domain) is a membrane-spanning protein domain. TMDs may consist of one or several alpha-helices or a transmembrane beta barrel. Because the interior of the lipid bilayer is hydrophobic, the amino acid residues in ...

, and a cytoplasmic domain with predicted

serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − ...

threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form when dissolved in water), a carboxyl group (which is in the deprotonated −COO− ...

specificity. Type I receptors are essential for signaling; type II receptors are required for binding

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s and for expression of type I receptors. Type I and II receptors form a stable complex after ligand binding, resulting in

phosphorylation In biochemistry, phosphorylation is described as the "transfer of a phosphate group" from a donor to an acceptor. A common phosphorylating agent (phosphate donor) is ATP and a common family of acceptor are alcohols: : This equation can be writ ...

of type I receptors by type II receptors. This gene encodes activin A type I receptor that signals a particular transcriptional response in concert with activin type II receptors.

Signaling

ACVR1 transduces signals of BMPs. BMPs bind either

ACVR2A Activin receptor type-2A is a protein that in humans is encoded by the ''ACVR2A'' gene. ACVR2A is an activin type 2 receptor. Function This gene encodes activin A type II receptor. Activins are dimeric growth and differentiation factors which ...

/ ACVR2B or a BMPR2 and then form a complex with ACVR1. These go on to recruit the

R-SMAD R-SMADs are receptor-regulated SMADs. SMADs are transcription factors that transduce extracellular TGF-β superfamily ligand signaling from cell membrane bound TGF-β receptors into the nucleus where they activate transcription TGF-β target ge ...

SMAD1 Mothers against decapentaplegic homolog 1 also known as SMAD family member 1 or SMAD1 is a protein that in humans is encoded by the ''SMAD1'' gene. Nomenclature SMAD1 belongs to the SMAD (protein), SMAD, a family of proteins similar to the gene p ...

SMAD2 Mothers against decapentaplegic homolog 2, also known as SMAD family member 2 or SMAD2, is a protein that in humans is encoded by the ''SMAD2'' gene. MAD homolog 2 belongs to the SMAD, a family of proteins similar to the gene products of the ''Dr ...

SMAD3 Mothers against decapentaplegic homolog 3 also known as SMAD family member 3 or SMAD3 is a protein that in humans is encoded by the SMAD3 gene. SMAD3 is a member of the SMAD (protein), SMAD family of proteins. It acts as a mediator of the signal ...

SMAD6 SMAD family member 6, also known as SMAD6, is a protein that in humans is encoded by the ''SMAD6'' gene. SMAD6 is a protein that, as its name describes, is a homolog of the Drosophila gene " mothers against decapentaplegic". It belongs to the SM ...

Clinical significance

Gain-of-function mutations in the gene ACVR1/ALK2 is responsible for the genetic disease fibrodysplasia ossificans progressiva (FOP). The typical FOP patient has the amino acid

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

substituted for the amino acid

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an Amine, α-amino group (which is in the protonated –NH3+ form under Physiological condition, biological conditions), a carboxylic ...

at position 206 in this protein. This substitution causes a change in the critical

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

activation domain of the protein that will then cause the protein to bind its inhibitory ligand (

FKBP The FKBPs, or FK506 binding proteins, constitute a family of proteins that have prolyl isomerase activity and are related to the cyclophilins in function, though not in amino acid sequence. FKBPs have been identified in many eukaryotes, rangin ...

12) less tightly, and thus overactivate the BMP/SMAD pathway. The result of this overactivation is that

endothelial cell The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and th ...

s transform to

mesenchymal stem cell Mesenchymal stem cells (MSCs), also known as mesenchymal stromal cells or medicinal signaling cells, are multipotent stromal cells that can Cellular differentiation, differentiate into a variety of cell types, including osteoblasts (bone cells), ...

s and then to bone. Atypical mutations involving other residues work similarly, thereby causing the protein to be stuck in its active conformation despite no BMP being present. Mutations in the ACVR1 gene have also been linked to cancer, especially

diffuse intrinsic pontine glioma Diffuse midline glioma, H3 K27-altered (DMG) is a tumour that arises in midline structures of the brain, most commonly the brainstem, thalamus and spinal cord. When located in the pons it is also known as diffuse intrinsic pontine glioma (DIPG). ...

(DIPG).

References

External links

* * {{DEFAULTSORT:Acvr1 GS domain TS domain S/T domain Human proteins EC 2.7.11