Histidine-rich glycoprotein (HRG) is one of the major plasma proteins and thought to function in blood coagulation, fibrinolysis, and innate immune systems. The amino acid sequence of HRG revealed a multidomain structure consisting of cystatin-like domains 1 and 2, a Pro-rich domain 1, a His-rich domain, a Pro-rich domain 2, and a C-terminal domain. Broad ligand-binding properties of HRG are involved in the multivalent functions of HRG. Among various functions of HRG, its interactions with heparin/heparan sulfate, fibrinogen, and plasminogen are thought to be intimately related to its roles in the coagulation and fibrinolytic systems. Recent studies on these topics are mainly reviewed in this article. The newly disclosed abilities of HRG in angiogenesis, its antibacterial effect, its activation of T-cell lines in cooperation with Concanavalin A, and the identification of a putative receptor for HRG on T cell lines are also described.
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