3pmh
Mechanism of Sulfotyrosine-Mediated Glycoprotein Ib Interaction with Two Distinct alpha-Thrombin Sites
Structural highlights
DiseaseTHRB_HUMAN Defects in F2 are the cause of factor II deficiency (FA2D) [MIM:613679. It is a very rare blood coagulation disorder characterized by mucocutaneous bleeding symptoms. The severity of the bleeding manifestations correlates with blood factor II levels.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] Genetic variations in F2 may be a cause of susceptibility to ischemic stroke (ISCHSTR) [MIM:601367; also known as cerebrovascular accident or cerebral infarction. A stroke is an acute neurologic event leading to death of neural tissue of the brain and resulting in loss of motor, sensory and/or cognitive function. Ischemic strokes, resulting from vascular occlusion, is considered to be a highly complex disease consisting of a group of heterogeneous disorders with multiple genetic and environmental risk factors.[13] Defects in F2 are the cause of thrombophilia due to thrombin defect (THPH1) [MIM:188050. It is a multifactorial disorder of hemostasis characterized by abnormal platelet aggregation in response to various agents and recurrent thrombi formation. Note=A common genetic variation in the 3-prime untranslated region of the prothrombin gene is associated with elevated plasma prothrombin levels and an increased risk of venous thrombosis. Defects in F2 are associated with susceptibility to pregnancy loss, recurrent, type 2 (RPRGL2) [MIM:614390. A common complication of pregnancy, resulting in spontaneous abortion before the fetus has reached viability. The term includes all miscarriages from the time of conception until 24 weeks of gestation. Recurrent pregnancy loss is defined as 3 or more consecutive spontaneous abortions.[14] FunctionTHRB_HUMAN Thrombin, which cleaves bonds after Arg and Lys, converts fibrinogen to fibrin and activates factors V, VII, VIII, XIII, and, in complex with thrombomodulin, protein C. Functions in blood homeostasis, inflammation and wound healing.[15] Publication Abstract from PubMedThe involvement of exosite I in alpha-thrombin (FIIa) binding to platelet glycoprotein Ibalpha (GPIbalpha), which could influence interactions with other substrates, remains undefined. To address the problem, we generated the GPIbalpha amino terminal domain (GPIbalpha-N) fully sulfated on three tyrosine residues and solved the structure of its complex with FIIa. We found that sulfotyrosine (Tys) 278 enhances the interaction mainly by establishing contacts with exosite I. We then evaluated how substituting tyrosine with phenylalanine, which cannot be sulfated, affects FIIa binding to soluble or surface-immobilized GPIbalpha-N. Mutating Tyr(276), which mostly contacts exosite II residues, markedly reduced FIIa interaction with both soluble and immobilized GPIbalpha-N; mutating Tyr(278) or Tyr(279), which mostly contact exosite I residues, reduced FIIa complexing in solution by 0-20% but affinity for immobilized GPIbalpha-N 2 to 6-fold, respectively. Moreover, three exosite I ligands-aptamer HD1, hirugen, and lepirudin-did not interfere with soluble FIIa complexing to GPIbalpha-N, excluding that their binding caused allosteric effects influencing the interaction; nonetheless, all impaired FIIa binding to immobilized GPIbalpha-N and platelet GPIb nearly as much as aptamer HD22 and heparin, both exosite II ligands. Bound HD1 and hirugen alter Trp(148) orientation in a loop near exosite I preventing contacts with the sulfate oxygen atoms of Tys(279). These results support a mechanism in which binding occurs when the two exosites of one FIIa molecule independently interact with two immobilized GPIbalpha molecules. Through exosite engagement, GPIbalpha may influence FIIa-dependent processes relevant to hemostasis and thrombosis. Binding of {alpha}-thrombin to surface-anchored platelet glycoprotein Ib{alpha} sulfotyrosines through a two-site mechanism involving exosite I.,Zarpellon A, Celikel R, Roberts JR, McClintock RA, Mendolicchio GL, Moore KL, Jing H, Varughese KI, Ruggeri ZM Proc Natl Acad Sci U S A. 2011 May 24;108(21):8628-33. Epub 2011 May 9. PMID:21555542[16] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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