title: Allosteric activation of antithrombin is independent of charge neutralization or reversal in the heparin binding site.
abstract: We investigate the hypothesis that heparin activates antithrombin (AT) by relieving electrostatic strain within helix D. Mutation of residues K125 and R129 to either Ala or Glu abrogated heparin binding, but did not activate AT towards inhibition of factors IXa or Xa. However, substitution of residues C-terminal to helix D (R132 and K133) to Ala had minimal effect on heparin affinity but resulted in appreciable activation. We conclude that charge neutralization or reversal in the heparin binding site does not drive the activating conformational change of AT, and that the role of helix D elongation is to stabilize the activated state.
authors.affiliation: University of Cambridge, Department of Haematology, Cambridge Institute for Medical Research, Division of Structural Medicine, Wellcome Trust/MRC Building, Cambridge CB2 2XY, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Langdown
authors.forename: Wendy J
authors.initials: WJ
authors.lastname: Carter
authors.forename: Trevor P
authors.initials: TP
authors.lastname: Baglin
authors.forename: James A
authors.initials: JA
authors.lastname: Huntington
mesh_terms: D000494:Allosteric Regulation; D000991:Antithrombins / Q000502:physiology*; D001665:Binding Sites; D006487:Hemostasis; D006493:Heparin / Q000378:metabolism*; D055672:Static Electricity
chemical_list: D000991:Antithrombins; D006493:Heparin