Vitronectin
Template:Short description Script error: No such module "redirect hatnote". Template:Cs1 config Template:Infobox gene Vitronectin (VTN or VN) is a glycoprotein of the hemopexin family which is synthesized and excreted by the liver, and abundantly found in serum, the extracellular matrix and bone.[1] In humans it is encoded by the VTN gene.[2][3]
Vitronectin binds to integrin alpha-V beta-3 and thus promotes cell adhesion and spreading. It also inhibits the membrane-damaging effect of the terminal cytolytic complement pathway and binds to several serpins (serine protease inhibitors). It is a secreted protein and exists in either a single chain form or a clipped, two chain form held together by a disulfide bond.[2] Vitronectin has been speculated to be involved in hemostasis[4] and tumor malignancy.[5][6]
Structure
Vitronectin is a 75 kDa glycoprotein, consisting of 478 amino acid residues. About one-third of the protein's molecular mass is composed of carbohydrates. On occasion, the protein is cleaved after arginine 379, to produce two-chain vitronectin, where the two parts are linked by a disulfide bond. No high-resolution structure has been determined experimentally yet, except for the N-terminal domain.
The protein consists of three domains:
- The N-terminal Somatomedin B domain (1-39)
- A central domains with hemopexin homology (131-342)
- A C-terminal domain (residues 347-459) also with hemopexin homology.
Several structures has been reported for the Somatomedin B domain. The protein was initially crystallized in complex with one of its physiological binding partners: the Plasminogen activator inhibitor-1 (PAI-1) and the structure solved for this complex.[7] Subsequently two groups reported NMR structures of the domain.[8][9]
The somatomedin B domain is a close-knit disulfide knot, with 4 disulfide bonds within 35 residues. Different disulfide configurations had been reported for this domain[10][11][12] but this ambiguity has been resolved by the crystal structure.[12]
Homology models have been built for the central and C-terminal domains.[12]
Function
The somatomedin B domain of vitronectin binds to plasminogen activator inhibitor-1 (PAI-1), and stabilizes it.[7] Thus vitronectin serves to regulate proteolysis initiated by plasminogen activation. In addition, vitronectin is a component of platelets and is, thus, involved in hemostasis. Vitronectin contains an RGD (45-47) sequence, which is a binding site for membrane-bound integrins, e.g., the vitronectin receptor, which serve to anchor cells to the extracellular matrix. The Somatomedin B domain interacts with the urokinase receptor, and this interaction has been implicated in cell migration and signal transduction. High plasma levels of both PAI-1 and the urokinase receptor have been shown to correlate with a negative prognosis for cancer patients. Cell adhesion and migration are directly involved in cancer metastasis, which provides a probable mechanistic explanation for this observation.
References
Further reading
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External links
Template:PDB Gallery Template:Glycoproteins Template:Fibrous proteins
- ↑ Boron, Walter F. and Boulpaep, Emile L. "Medical Physiology". Saunders, 2012, p.1097.
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