Aspartic acid residues 72 and 75 and tyrosine-sulfate 73 of heparin cofactor II promote intramolecular interactions during glycosaminoglycan binding and thrombin inhibition

J Biol Chem. 2002 May 31;277(22):19823-30. doi: 10.1074/jbc.M200630200. Epub 2002 Feb 20.


We used site-directed mutagenesis to investigate the role of Glu(69), Asp(70), Asp(71), Asp(72), Tyr-sulfate(73), and Asp(75) in the second acidic region (AR2) of the serpin heparin cofactor II (HCII) during formation of the thrombin.HCII complex with and without glycosaminoglycans. E69Q/D70N/D71N recombinant (r)HCII, D72N/Y73F/D75N rHCII, and E69Q/D70N/D71N/D72N/Y73F/D75N rHCII were prepared to localize acidic residues important for thrombin inhibition. Interestingly, D72N/Y73F/D75N rHCII had significantly enhanced thrombin inhibition without glycosaminoglycan (4-fold greater) and with heparin (6-fold greater), showing maximal activity at 2 microg/ml heparin compared with wild-type recombinant HCII (wt-rHCII) with maximal activity at 20 microg/ml heparin. The other rHCII mutants had lesser-enhanced activities, but they all eluted from heparin-Sepharose at significantly higher ionic strengths compared with wt-rHCII. Neutralizing and reversing the charge of Asp(72), Tyr-sulfate(73), and Asp(75) were done to characterize their individual contribution to HCII activity. Only Y73K rHCII and D75K rHCII have significantly increased heparin cofactor activity compared with wt-rHCII; however, all of the individual rHCII mutants required substantially less glycosaminoglycan at maximal inhibition than did wt-rHCII. Inhibition of either alpha-thrombin/hirugen or gamma(T)-thrombin (both with an altered anion-binding exosite-1) by the AR2 rHCII mutants was similar to wt-rHCII. D72N/Y73F/D75N rHCII and D75K rHCII were significantly more active than wt-rHCII in a plasma-based thrombin inhibition assay with glycosaminoglycans. These results indicate that improved thrombin inhibition in the AR2 HCII mutants is mediated by enhanced interactions between the acidic domain and anion-binding exosite-1 of thrombin and that AR2 may be a "molecular rheostat" to promote thrombin inhibition in the presence of glycosaminoglycans.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Anions
  • Aspartic Acid / chemistry*
  • Binding Sites
  • Chymotrypsin / antagonists & inhibitors
  • Dermatan Sulfate / pharmacology
  • Dose-Response Relationship, Drug
  • Glycosaminoglycans / chemistry*
  • Glycosaminoglycans / metabolism
  • Heparin / chemistry
  • Heparin / metabolism
  • Heparin Cofactor II / chemistry*
  • Humans
  • Ions
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Mutation
  • Protein Binding
  • Recombinant Proteins / metabolism
  • Thrombin / antagonists & inhibitors
  • Thrombin / metabolism*
  • Tyrosine / analogs & derivatives
  • Tyrosine / chemistry
  • Tyrosine / metabolism*


  • Anions
  • Glycosaminoglycans
  • Ions
  • Recombinant Proteins
  • Dermatan Sulfate
  • tyrosine O-sulfate
  • Aspartic Acid
  • Tyrosine
  • Heparin Cofactor II
  • Heparin
  • Chymotrypsin
  • Thrombin