4bak | pdb_00004bak
Thrombin in complex with inhibitor
Structural highlights
Disease[THRB_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] Function[THRB_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] [HIRV1_HIRME] Hirudin is a potent thrombin-specific protease inhibitor. It forms a stable non-covalent complex with alpha-thrombin, thereby abolishing its ability to cleave fibrinogen.[16] Publication Abstract from PubMedFor improved understanding of drug-target interactions, the effect of introducing substituted amine residues with increased chain length in the P3 residue of the thrombin inhibitor melagatran was explored. Inhibition, kinetic and thermodynamic data obtained via stopped-flow spectroscopy (SF), isothermal microcalorimetry (ITC) and surface plasmon resonance (SPR) biosensor analysis were interpreted with the help of X-ray crystal structures of the enzyme inhibitor complexes. The association rate became faster when increasing the lipophilicity of the inhibitors. This was coupled to an increased enthalpic component and a corresponding decreased entropic component. The dissociation rates were reduced upon increasing the chain length, with only a smaller increase and decrease of the enthalpic and entropic components, respectively. Overall, the affinity increased with increasing chain length, with similar changes in the enthalpic and entropic components. ITC analysis confirmed the equilibrium data from SPR analysis, showing that melagatran was the most enthalpy driven interaction. Structural analysis of the thrombin-inhibitor complex showed that the orientation of the P1 and P2 parts of the molecules was very similar, but that there were significant differences in the interaction between the terminal part of the P3 side chain and the binding pocket. A combination of charge repulsion, H-bonds and hydrophobic interactions could be used to explain the observed kinetic and thermodynamic profiles for the ligands. In conclusion, changes in the structure of a lead compound can have significant effects on its interaction with the target that translate directly into kinetic and thermodynamic effects. In contrast to what may be intuitively expected, hydrogen bond formation and breakage is not necessarily reflected in enthalpy gains and losses, respectively. Identification of Structure-Kinetic and Structure-Thermodynamic Relationships for Thrombin Inhibitors.,Winquist J, Geschwindner S, Xue Y, Gustavsson L, Musil D, Deinum J, Danielson UH Biochemistry. 2013 Jan 4. PMID:23290007[17] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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