Histidine-rich glycoprotein
Domain
The His/Pro-rich (HRR) region contains approximately 12 tandem internal repeats of the 5-residue G[H/P][H/P]PH consensus sequence. HRR binds heparan sulfate and possesses antiangiogenic, antibacterial and antifungal properties through binding Candida cells, and preferentially lysing the ergosterol-containing liposomes at low pH. The tandem repeats also bind divalent metal ions and heme.
The cystatin domains can also bind heparan sulfate. Binding is enhanced in the presence of zinc ions.
Function
Plasma glycoprotein that binds a number of ligands such as heme, heparin, heparan sulfate, thrombospondin, plasminogen, and divalent metal ions. Binds heparin and heparin/glycosaminoglycans in a zinc-dependent manner. Binds heparan sulfate on the surface of liver, lung, kidney and heart endothelial cells. Binds to N-sulfated polysaccharide chains on the surface of liver endothelial cells. Inhibits rosette formation. Acts as an adapter protein and is implicated in regulating many processes such as immune complex and pathogen clearance, cell chemotaxis, cell adhesion, angiogenesis, coagulation and fibrinolysis. Mediates clearance of necrotic cells through enhancing the phagocytosis of necrotic cells in a heparan sulfate-dependent pathway. This process can be regulated by the presence of certain HRG ligands such as heparin and zinc ions. Binds to IgG subclasses of immunoglobins containing kappa and lambda light chains with different affinities regulating their clearance and inhibiting the formation of insoluble immune complexes. Tethers plasminogen to the cell surface. Binds T-cells and alters the cell morphology. Modulates angiogenesis by blocking the CD6-mediated antiangiongenic effect of thrombospondins, THBS1 and THBS2. Acts as a regulator of the vascular endothelial growth factor (VEGF) signaling pathway; inhibits endothelial cell motility by reducing VEGF-induced complex formation between PXN/paxillin and ILK/integrin-linked protein kinase and by promoting inhibition of VEGF-induced tyrosine phosphorylation of focal adhesion kinases and alpha-actinins in endothelial cells. Also plays a role in the regulation of tumor angiogenesis and tumor immune surveillance. Normalizes tumor vessels and promotes antitumor immunity by polarizing tumor-associated macrophages, leading to decreased tumor growth and metastasis.
Involvement in disease
Thrombophilia due to histidine-rich glycoprotein deficiency
THPH11
A hemostatic disorder characterized by a tendency to thrombosis.
None
The disease is caused by variants affecting the gene represented in this entry.
Post-translational modifications
Proteolytic cleavage produces several HRG fragments which are mostly disulfide-linked and, therefore, not released. Cleavage by plasmin is inhibited in the presence of heparin, zinc ions or in an acidic environment. Cleavage reduces binding of HRG to heparan sulfate, but enhances the ability of HRG to bind and tether plasminogen to the cell surface. On platelet activation, releases a 33 kDa antiangiogenic peptide which encompasses the HRR. Also cleaved in the C-terminal by plasmin.
N-glycosylated.
Tissue Specificity
Expressed in macrophages and in malignant cells. Expressed by the liver and secreted in plasma (at protein level).
Cellular localization
- Secreted
Alternative names
Histidine-rich glycoprotein, Histidine-proline-rich glycoprotein, HPRG, HRG