3dux
Understanding Thrombin Inhibition
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] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedSuccessful design of potent and selective protein inhibitors, in terms of structure-based drug design, strongly relies on the correct understanding of the molecular features determining the ligand binding to the target protein. We present a case study of serine protease inhibitors with a bis(phenyl)methane moiety binding into the S3 pocket. These inhibitors bind with remarkable potency to the active site of thrombin, the blood coagulation factor IIa. A combination of X-ray crystallography and isothermal titration calorimetry provides conclusive insights into the driving forces responsible for the surprisingly high potency of these inhibitors. Analysis of six well-resolved crystal structures (resolution 1.58-2.25 A) along with the thermodynamic data allows an explanation of the tight binding of the bis(phenyl)methane inhibitors. Interestingly, the two phenyl rings contribute to binding affinity for very different reasons - a fact that can only be elucidated by a structure-based approach. The first phenyl moiety occupies the hydrophobic S3 pocket, resulting in a mainly entropic advantage of binding. This observation is based on the displacement of structural water molecules from the S3 pocket that are observed in complexes with inhibitors that do not bind in the S3 pocket. The same classic hydrophobic effect cannot explain the enhanced binding affinity resulting from the attachment of the second, more solvent-exposed phenyl ring. For the bis(phenyl)methane inhibitors, an observed adaptive rotation of a glutamate residue adjacent to the S3 binding pocket attracted our attention. The rotation of this glutamate into salt-bridging distance with a lysine moiety correlates with an enhanced enthalpic contribution to binding for these highly potent thrombin binders. This explanation for the magnitude of the attractive force is confirmed by data retrieved by a Relibase search of several thrombin-inhibitor complexes deposited in the Protein Data Bank exhibiting similar molecular features. Special attention was attributed to putative changes in the protonation states of the interaction partners. For this purpose, two analogous inhibitors differing mainly in their potential to change the protonation state of a hydrogen-bond donor functionality were compared. Buffer dependencies of the binding enthalpy associated with complex formation could be traced by isothermal titration calorimetry, which revealed, along with analysis of the crystal structures (resolution 1.60 and 1.75 A), that a virtually compensating proton interchange between enzyme, inhibitor and buffer is responsible for the observed buffer-independent thermodynamic signatures. Think twice: understanding the high potency of bis(phenyl)methane inhibitors of thrombin.,Baum B, Muley L, Heine A, Smolinski M, Hangauer D, Klebe G J Mol Biol. 2009 Aug 21;391(3):552-64. Epub 2009 Jun 9. PMID:19520086[16] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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