The heparin-binding site(s) of histidine-rich glycoprotein as suggested by sequence homology with antithrombin III

A high degree of sequence homology has been found between the N-terminal region of histidine-rich glycoprotein (HRG) and that of antithrombin III (AT III) where the putative heparin-binding site of AT III is located. The amino acid residue at the position corresponding to Arg-47 of AT III that is essential for the heparin-binding was also arginine (Arg 23 and 78) in the homologous sequences of HRG. These observations strongly suggest that the heparin-binding sites of HRG and AT III are evolutionarily related. There was no apparent sequence similarity between the remaining about 70% portions of the two proteins.