Vitronectin
Vitronectin (VN) is a multifunctional glycoprotein of 75 kD that binds to various biological ligands and plays a key role in tissue remodeling by regulating cell adhesion through binding to different types of integrins, mainly via the RGD sequence.
From: Comprehensive Biomaterials II, 2017
Related terms:
Scleroprotein
Peptide
Protein
Protein S
Von Willebrand Factor
Fibrinogen
Fibronectin
Laminin
Ligand
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Vitronectin
Yu-Ching Su, Kristian Riesbeck, in The Complement FactsBook, 2018
Abstract
The multifaceted complement regulator vitronectin (Vn) can be found in almost all tissues of the human body. It is primarily produced by the liver and is thus detected at high concentrations in plasma. Upon inflammation, Vn is upregulated revealing its importance for the innate immune defence against danger signals. It consists of 459 amino acids and has several key sequences linked to its functions. Vn interacts at its N-terminal with plasminogen activator inhibitor-1 and urokinase-type plasminogen activator receptor (uPAR). Downstream of these binding sites are sequences that attract integrins and collagen in addition to the thrombin–antithrombin III complex. Heme-binding plasma proteins, as well as plasminogen, can also interact with Vn through heparin-binding domains. One of the main functions of Vn is to inhibit the terminal pathway of the complement system by preventing formation of the lethal pore-forming complex. This chapter will in detail discuss the knowledge on this important molecule.
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Platelet Thrombus Formation in Flowing Blood
Zaverio M. Ruggeri, Shaun P. Jackson, in Platelets (Third Edition), 2013
4 Platelet Adhesion to Vitronectin
Vitronectin is a fairly abundant plasma protein, produced and secreted by the liver, that under physiopathological conditions associates with cell surfaces—for example, it binds to activated platelets153—and with extracellular matrices of various tissues.154 Vitronectin becomes incorporated into blood clots; in experimental conditions, purified multimeric vitronectin incorporated into fibrin enhances platelet adhesion and local aggregation.15 The direct contribution of vitronectin to platelet aggregation has been controversial, but the study of vitronectin-deficient mice has helped clarify the issue.155 In ex vivo experiments, thrombin-induced aggregation of plasma-free platelets from vitronectin-deficient mice was impaired, but ADP-induced aggregation of vitronectin-deficient platelet-rich plasma was enhanced as compared to normal. This enhancement was reduced by adding plasma-derived vitronectin; thus, platelet-released vitronectin may contribute to aggregation, and plasma vitronectin may be inhibitory. Moreover, in vivo studies demonstrated that thrombi formed in response to vascular injury were unstable in the absence of vitronectin, resulting in delayed vessel occlusion and frequent reopening.156 Vitronectin binds to and stabilizes plasminogen activator inhibitor-1 (PAI-1) and may protect fibrin from lysis acting as a thrombus stabilizer. Indeed, the thrombotic phenotype of mice with a combined PAI-1 and vitronectin deficiency does not differ significantly from that of mice with the corresponding single defects, suggesting that PAI-1 and vitronectin may influence thrombus stability by regulating a common pathway.157
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Biologically Inspired and Biomolecular Materials
S. Bierbaum, D. Scharnweber, in Comprehensive Biomaterials, 2011
2.208.2.2.4 Vitronectin
VN is a multifunctional glycoprotein of 75 kDa that binds to various biological ligands and plays a key role in tissue remodeling by regulating cell adhesion through binding to different types of integrins, mainly via the RGD sequence. VN also regulates blood-system-related protease cascades such as coagulation and fibrinolysis through interaction with heparin and thrombin–antithrombin III complexes. Tissue VN interacts with PGs and collagens, but plasma VN is believed to be in the inactive monomer form that does not bind, requiring activation through urea, heat, or certain ligands like heparin.19
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Biologically Inspired and Biomolecular Materials
S. Bierbaum, ... D. Scharnweber, in Comprehensive Biomaterials II, 2017
2.8.2.2.4 Vitronectin
Vitronectin (VN) is a multifunctional glycoprotein of 75 kD that binds to various biological ligands and plays a key role in tissue remodeling by regulating cell adhesion through binding to different types of integrins, mainly via the RGD sequence. Vitronectin also regulates blood system related protease cascades such as coagulation and fibrinolysis through interaction with heparin and thrombin-antithrombin III complexes. Tissue VN interacts with proteoglycans and collagens, but plasma VN is believed to be in the inactive monomer form that does not bind, requiring activation through urea, heat or certain ligands like heparin (Schvartz et al., 1999).
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The Regulatory Role of Matrix Proteins in Mineralization of Bone
WEI ZHU, ... ADELE L. BOSKEY, in Osteoporosis (Third Edition), 2008
c. Vitronectin
Vitronectin, also termed the S-protein of the complement system, is produced predominantly by the liver. It is found in serum at concentrations of 200–400 μg/mL and in bone matrices at low levels [322, 347]. Although it also appears in basement membranes, it is generally found in most matrices containing the fibrillar collagens.
The human gene encoding for vitronectin is located on chromosome 17q [348]. The protein has a molecular weight of ∼70 kDa, and the primary structure of human vitronectin was predicted from cDNA analysis by Oldberg et al. [349] and Jenne and Stanley [350]. Several homologous domains in the mammalian vitronectin sequences obtained from different sources have been defined [351]. From the amino to the carboxy terminus there is a "somatomedin B" domain which is rich in cysteines, followed by an RGD cell attachment site, a collagen-binding domain, a cross-linking site for transglutaminase, a plasminogen binding site, a heparin binding site, a PAI binding site, and an endogenous cleavage site. Sites for sulfation and cAMP-dependent phosphorylation are also present.
In vitro, vitronectin may be a biosynthetic product of osteoblastic cells [352]. Vitronectin is very active in mediating attachment of all cell types. Bone cells, including osteoclasts, attach very strongly to vitronectin [313, 322, 353, 354], mainly via the receptor integrin, αvβ3 [313, 353]. Vitronectin is detectable in developing bone by immunohistochemistry and is found in a very limited number of cells lying on the surface of newly formed bone [352]. However, it is not clear that these cells are in fact osteoblasts. Mice deficient in the vitronectin gene have been shown to have a thrombolytic phenotype, but there is no report on whether skeletal defects were apparent in these mice [355].
Vitronectin inhibits secondary nucleation of apatite crystals in vitro [356], whereas a direct effect on mineral deposition has not been established. Bone matrix is only faintly stained by immunological techniques, indicating accumulation of vitronectin in matrix at very low levels [313]. However, prior to mineral deposition, vitronectin is increased in concentration in the unmineralized osteoid [352], implying that it may be involved in preparing the matrix for mineral deposition.
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Matrix Chemistry Controlling Stem Cell Behavior
Christina Klecker, Lakshmi S. Nair, in Biology and Engineering of Stem Cell Niches, 2017
2.7.2.3 Vitronectin
Vitronectin is considered a glycoprotein, although nearly 1/3 of the structure consists of carbohydrate chains. It is secreted predominantly by hepatocytes, with a single chain configuration, which may later be cleaved and reconnected with a disulfide bond. This molecule is active in many ways throughout the body, with major contributions during wound healing and tissue remodeling. In the blood stream, vitronectin is capable of binding and stabilizing plasminogen activator inhibitor-1, which leads to increased clot formation. In the ECM, it utilizes RGD sequences to bind with integrins on cells, facilitating their adhesion to the matrix using alternative binding domains.36
Previous studies have shown that vitronectin supports high rate of hMSCs adhesion within minutes of exposure.22 After confirming adequate interactions, the role of purified vitronectin on osteogenic differentiation of hMSCs was examined, in both basal and osteogenic media. It was observed that the presence of vitronectin could stimulate mineralization of hMSCs without any other inducing factors. Moreover, the cells expressed osteopontin and alkaline phosphatase activity, which indicate osteogenic differentiation. The study also demonstrated that the combined presence of vitronectin and collagen I could provide the most conducive environment for the osteogenic differentiation of hMSCs. Based on the data, researchers hypothesized that the mechanism for vitronectin's osteogenic influence is by integrin-mediated signaling, which upregulates the expression of collagen I within the cell. Once the matrix is enhanced with collagen, the synergistic effects of these two proteins enhanced the osteogenic differentiation of the hMSC. Moreover, the study also revealed that ECM/integrin binding initiates an ERK-dependent pathway, leading to increased expression of RUNX2 and CBFA1. Studies by this same group identified FAK signaling as the regulator for ERK activity in this process.37 Using a knockdown approach, the authors observed that without FAK signaling cascade, the osteogenic differentiation of hMSCs in the presence of vitronectin is substantially diminished.
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Sulphonated biomaterials as glycosaminoglycan mimics in wound healing
B.J. Tighe, A. Mann, in Advanced Wound Repair Therapies, 2011
13.5.6 Biochemical factors: vitronectin/plasmin effects
Vitronectin has an important pro-active role in modulating the conversion of plasminogen to plasmin. The plasminogen-plasmin activation process is kept in equilibrium via the anatagnostic activities of the plasminogen activator system and plasminogen activator inhibitor (PAI) system. The most significant plasminogen activator inhibitor in cellular systems is PAI-1 which binds to vitronectin, thus localising PAI-1 to the pericellular compartment where active plasminogen activator is generated (Vaheri et al., 2002). If vitronectin is localised on a surface adjacent to the cellular site (such as a chronic wound), it removes plasminogen activator inhibitor from the reaction by fixing it, creating an imbalance in favour of the plasminogen activator and a production of active plasmin. This results in local upregulation of plasmin formation. The phenomenon of plasmin upregulation has been known in relation to corneal wound healing and in conventional cosmetic lens wear for several years. (Chapter 12).
Because vitronectin is a sticky protein, once adsorbed on the biomaterial it remains there. The adsorption is very material-dependent and is promoted by high interfacial tension and the presence of hydrophobic domains within the material. Sulphonated biomimetic materials minimise this irreversible deposition. Increase in vitronectin associated with the material increases the potential for plasmin upregulation in the fluid held between material and tissue surface. The analogies between the cornea and the chronic wound have been outlined in Chapter 12. We have carried out extensive studies in this area, including the effect of sulphated biomimetic hydrogels in comparison with both neutral and carboxyl-containing hydrogels.
The conclusion in relation to hydrogel wound dressings seems clear and is supported by experience in studies of contact lens-cornea interactions. The presence of hydrophobic domains within neutral and carboxyl-containing hydrogels leads to irreversible deposition of vitronectin and its consequent depletion in the tissue bed. Since this depletes active PAI-1 there is a consequent upregulation of plasmin – and ultimately collagenase. In the eye this effect is minimised by sulphonated biomimetic materials – it is logical to expect the same to apply to hydrogel wound dressings.
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The Complement System
R.R. Kew, in Pathobiology of Human Disease, 2014
Regulation of the Terminal Pathway
•
Vitronectin is a multifunctional plasma protein that binds C5-7 complex and prevents C7 from binding to membrane phospholipids. The soluble vitronectin/C5b-7 is inactive and cannot generate an MAC (Figure 8).

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Figure 8. Regulation of the terminal (membrane attack) pathway. The pathway is regulated at the C7 binding step by clusterin or the vitronectin. CD59 (MIRL) regulates the pathway by preventing C8 and C9 from binding to the C5b-7 or C5b-8 complex.
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Clusterin (apo J) is also a multifunctional plasma protein that inhibits the terminal pathway by binding C5b-7 in a similar manner as the vitronectin.
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CD59 (also known as membrane inhibitor of reactive lysis, MIRL) is a cell-surface inhibitor that binds C5b-7 and blocks C8 from inserting into the membrane and/or binds C5b-8 and prevents C9 from binding and polymerizing. CD59, like DAF, is a GPI-anchored regulatory protein and is widely expressed on many different cell types.
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Evolution of SARS Coronavirus and the Relevance of Modern Molecular Epidemiology
Z. Shi, L.-F. Wang, in Genetics and Evolution of Infectious Diseases (Second Edition), 2017
5.3 Receptor Usage and Evolutionary Selection
The S protein of coronavirus is responsible for attachment to cellular receptor to initiate the first step of virus infection. The angiotensin-converting enzyme 2 (ACE2) was identified as a main functional receptor for SARS-CoV.45 Further analysis demonstrated that the region covering aa 318–520 of S protein is the key receptor-binding domain (RBD), which is both essential and sufficient to bind the human ACE2 molecule in vitro.46 Detailed analysis of the crystal structure of the RBD–ACE2 complex revealed that 19 key residues have close contact with the receptor molecule, which are located from aa 424 to 474. This region is termed the receptor-binding motif (RBM).47
When the existing epidemiological data was analyzed in combination with the data on infectivity of SARS-CoV isolated in humans at the different phases of the outbreaks and SARS-CoV isolates in civets, a clear correlation could be established between the evolution of the S proteins and virus infectivity. It was observed that the S protein is the fastest evolving protein of SARS-CoV during interspecies transmission from animal to human and in the following phases of human to human transmission. The majority of the mutations are located in the S1 domain (31 of a total of 48 SNVs), particularly in the RBD.1,46 The interaction analysis between the S proteins of different isolates and the ACE2 molecules demonstrated that two aa residues in the S protein, aa 479 and aa 487, played a key role in virus infectivity.48,49 For aa residue 479, all 2002–2003 human isolates contain asparagine (N). The palm civet isolates seem to have variable aa residues at this position, all 2002–2003 and some 2003–2004 civet isolates have lysine (K) while other 2003–2004 isolates have either asparagine (N) or arginine (R). For aa residue 487, all isolates including those from early- and middle-phase patients, civets of 2002–2003 and 2003–2004, have a codon for serine (S), whereas all isolates from 2002–2003 late-phase human patients have a codon for threonine (T) (Fig. 26.3). When examined using an HIV-based pseudovirus infection assay, S proteins with all combinations of residues 487/479 could efficiently use the civet ACE2 as an entry receptor, but showed different infectivity in human ACE2-mediated infection.48,49 The combination of N479/T487 had the highest infectivity, N479/S487 medium infectivity, and K479/S487 the lowest, which almost abolished the infection. These results demonstrated elegantly at the molecular interface that the rapid evolution of the S protein, especially at the aa positions important for host receptor engagement, was essential for the adaptation to and establishment of an effective and productive human infection.
When the genome sequences of SL-CoVs were analyzed, it became evident that the N-terminal regions of their S proteins are the most divergent among themselves, as well as with the SARS-CoV. As shown in Fig. 26.3, bat SL-CoVs can be grouped into three groups based on the RBM sequences. The strains discovered early are close to each other and have a major sequence difference involving deletions of 17–18 aa right in the middle of RBM. We have since demonstrated experimentally that SL-CoV S proteins are unable to use ACE2 molecule, regardless of its origin, as a functional receptor. The second group, identified from European bats, has deletions of 4 aa.32 The third group, discovered recently, has no deletion and contains an identical size as the SARS-CoV in the S protein (Fig. 26.3).31,34,35 As predicted from their S sequences, three isolates from the third group, SL-CoV—WIV1, WIV16, and SHC014, have been shown to be able to use ACE2 for cellular entry, even though these S proteins still have slight difference at the key aa involved in direct interaction with ACE2.31,34,50 Most importantly, the SHC014 can replicate well in transgenic mice containing human ACE2, and it caused tissue damage in tested animals.50
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Toroviruses (Coronaviridae)
K.-O. Cho, A.E. Hoet, in Reference Module in Biomedical Sciences, 2014
Post-Translational Processing
The N-glycosylated spike (S) protein is derived from the processing of a 200 kDa precursor present in infected cells, but not in virions. Eighteen potential N-glycosylation sites, two heptad repeat domains, and a possible 'trypsin-like' cleavage site exist in the spike protein amino acid sequence. The mature S protein consists of two subunits and their electrophoretic mobility upon endoglycosidase F treatment suggests that the predicted cleavage site is functional in vivo. The heptad repeat domains are probably involved in the generation of an intra-chain coiled-coil secondary structure; similar interchain interactions can play a role in the formation of the observed S protein dimers. The intra- and interchain coiled-coil interactions may stabilize the stalk of the torovirus peplomers.
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