Vitronectin (VTN)

Vitronectin(VTN) is a glycoprotein synthesized by hepatocytes with a 75 kDa molecular weight and it circulates predominantly as an internally folded and stabilized monomer. VTN is a crucial component of the human extracellular matrix (ECM) and is produced in the liver and secreted into plasma. The N-terminal part of the VTN is composed of a somatomedin-B (SMB) domain followed by a cell receptor binding site characterized by an Arg-Gly-Asp (RGD) sequence. VTN contains four haemopexin-like domains which are predicted as putative haem-binding motifs with unknown function.

Vitronectin acts as an essential part of several biological processes, such as cell migration, adhesion, and angiogenesis. Importantly, it is also participating in the regulation of the terminal pathway of complement activation to limit the self-reactivity of the innate immune response. Recently, researchers have demonstrated that many bacterial species interact with VTN, but the functionality of these interactions in pathogenesis has not been fully elucidated. Furthermore, it is also showed that VTN can promote cellular adhesion by interactions with the integrins αvβ1, αvβ3, αvβ5, and αIIbβ3. And, VTN is found at low concentrations in normal extracellular matrices but is raised in chronic inflammatory liver disease where its deposition in the sinusoids is indicative of progressive fibrosis.

Fig.1 Role of VTN as a regulatory molecule for the complement system. (Singh, 2010)

Reference

1. Singh, B., et al. Vitronectin in bacterial pathogenesis: a host protein used in complement escape and cellular invasion. Molecular microbiology. 2010, 78(3), 545-560.