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Youngman NJ, Walker A, Naude A, Coster K, Sundman E, Fry BG. Varespladib (LY315920) neutralises phospholipase A 2 mediated prothrombinase-inhibition induced by Bitis snake venoms. Comp Biochem Physiol C Toxicol Pharmacol 2020; 236:108818. [PMID: 32512199 DOI: 10.1016/j.cbpc.2020.108818] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 05/26/2020] [Accepted: 06/02/2020] [Indexed: 01/28/2023]
Abstract
Anticoagulant toxicity is a common function of venoms produced by species within the Bitis genus. Potent inhibition of the prothrombinase complex is an identified mechanism of action for the dwarf species B. cornuta and B. xeropaga, along with some localities of B. atropos and B. caudalis. Snake venom phospholipase A2 toxins that inhibit the prothrombinase complex have been identified in snake venom, including an isolated phospholipase A2 toxin from B. caudalis. Current research is investigating the ability of the drug varespladib to inhibit snake venom phospholipase A2 toxins and reduce their toxicity. In particular, varespladib is being investigated as a treatment that could be administered prior to hospital referral which is a major necessity for species such as those from the genus Bitis, due to envenomations often occurring in remote regions of Africa where antivenom is unavailable. Using previously validated coagulation assays, this study aimed to determine if the toxins responsible for inhibition of the prothrombinase complex in the venom of four Bitis species are phospholipase A2 toxins, and if varespladib is able to neutralise this anticoagulant activity. Our results demonstrate that varespladib strongly neutralises the prothrombinase-inhibiting effects of all venoms tested in this study, and that this prothrombinase-inhibiting mechanism of anticoagulant activity is driven by phospholipase A2 class toxins in these four species. This study extends previous reports demonstrating varespladib has broad efficacy for treatment of phospholipase A2 rich snake venoms, indicating it also inhibits their anticoagulant effects mediated by prothrombinase-inhibition.
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Affiliation(s)
- Nicholas J Youngman
- Venom Evolution Lab, School of Biological Sciences, University of Queensland, St Lucia, QLD 4072, Australia
| | - Andrew Walker
- Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Arno Naude
- Snakebite Assist, Pretoria ZA-0001, South Africa
| | | | - Eric Sundman
- Universeum, Södra Vägen 50, 412 54 Gothenburg, Sweden
| | - Bryan G Fry
- Venom Evolution Lab, School of Biological Sciences, University of Queensland, St Lucia, QLD 4072, Australia.
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2
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Mud in the blood: Novel potent anticoagulant coagulotoxicity in the venoms of the Australian elapid snake genus Denisonia (mud adders) and relative antivenom efficacy. Toxicol Lett 2019; 302:1-6. [DOI: 10.1016/j.toxlet.2018.11.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Revised: 11/23/2018] [Accepted: 11/26/2018] [Indexed: 11/18/2022]
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3
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Billur R, Ban D, Sabo TM, Maurer MC. Deciphering Conformational Changes Associated with the Maturation of Thrombin Anion Binding Exosite I. Biochemistry 2017; 56:6343-6354. [PMID: 29111672 DOI: 10.1021/acs.biochem.7b00970] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Thrombin participates in procoagulation, anticoagulation, and platelet activation. This enzyme contains anion binding exosites, ABE I and ABE II, which attract regulatory biomolecules. As prothrombin is activated to thrombin, pro-ABE I is converted into mature ABE I. Unexpectedly, certain ligands can bind to pro-ABE I specifically. Moreover, knowledge of changes in conformation and affinity that occur at the individual residue level as pro-ABE I is converted to ABE I is lacking. Such changes are transient and were not captured by crystallography. Therefore, we employed nuclear magnetic resonance (NMR) titrations to monitor development of ABE I using peptides based on protease-activated receptor 3 (PAR3). Proton line broadening NMR revealed that PAR3 (44-56) and more weakly binding PAR3G (44-56) could already interact with pro-ABE I on prothrombin. 1H-15N heteronuclear single-quantum coherence NMR titrations were then used to probe binding of individual 15N-labeled PAR3G residues (F47, E48, L52, and D54). PAR3G E48 and D54 could interact electrostatically with prothrombin and tightened upon thrombin maturation. The higher affinity for PAR3G D54 suggests the region surrounding thrombin R77a is better oriented to bind D54 than the interaction between PAR3G E48 and thrombin R75. Aromatic PAR3G F47 and aliphatic L52 both reported on significant changes in the chemical environment upon conversion of prothrombin to thrombin. The ABE I region surrounding the 30s loop was more affected than the hydrophobic pocket (F34, L65, and I82). Our NMR titrations demonstrate that PAR3 residues document structural rearrangements occurring during exosite maturation that are missed by reported X-ray crystal structures.
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Affiliation(s)
- Ramya Billur
- Department of Chemistry, University of Louisville , Louisville, Kentucky 40292, United States
| | - David Ban
- Department of Medicine, James Graham Brown Cancer Center, University of Louisville , Louisville, Kentucky 40202, United States
| | - T Michael Sabo
- Department of Medicine, James Graham Brown Cancer Center, University of Louisville , Louisville, Kentucky 40202, United States
| | - Muriel C Maurer
- Department of Chemistry, University of Louisville , Louisville, Kentucky 40292, United States
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De Paula VS, Silva FHS, Francischetti IMB, Monteiro RQ, Valente AP. Recombinant expression of Ixolaris, a Kunitz-type inhibitor from the tick salivary gland, for NMR studies. Protein Expr Purif 2017; 139:49-56. [PMID: 28734839 DOI: 10.1016/j.pep.2017.07.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 06/29/2017] [Accepted: 07/17/2017] [Indexed: 11/16/2022]
Abstract
Ixolaris is an anticoagulant protein identified in the tick saliva of Ixodes scapularis. Ixolaris contains 2 Kunitz like domains and binds to Factor Xa or Factor X as a scaffold for inhibition of the Tissue Factor (TF)/Factor VIIa (FVIIa). In contrast to tissue factor pathway inhibitor (TFPI), however, Ixolaris does not bind to the active site cleft of FXa. Instead, complex formation is mediated by the FXa heparin-binding exosite. Due to its potent and long-lasting antithrombotic activity, Ixolaris is a promising agent for anticoagulant therapy. Although numerous functional studies of Ixolaris exist, three-dimensional structure of Ixolaris has not been obtained at atomic resolution. Using the pET32 vector, we successfully expressed a TRX-His6-Ixolaris fusion protein. By combining Ni-NTA chromatography, enterokinase protease cleavage, and reverse phase HPLC (RP-HPLC), we purified isotopically labeled Ixolaris for NMR studies. 1D 1H and 2D 15N-1H NMR analysis yielded high quality 2D 15N-1H HSQC spectra revealing that the recombinant protein is folded. These studies represent the first steps in obtaining high-resolution structural information by NMR for Ixolaris enabling the investigation of the molecular basis for Ixolaris-coagulation factors interactions.
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Affiliation(s)
- V S De Paula
- Campus Xerém, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 25245-390, Brazil; Centro de Biologia Estrutural e Bioimagem, Rio de Janeiro, 21941-920, Brazil
| | - F H S Silva
- Centro de Biologia Estrutural e Bioimagem, Rio de Janeiro, 21941-920, Brazil; Instituto de Bioquímica Médica, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, 21941-920, Brazil
| | - I M B Francischetti
- Vector Biology Section, Laboratory of Malaria and Vector Research (LMVR), National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH), Bethesda, MD, United States
| | - R Q Monteiro
- Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-902, Brazil
| | - A P Valente
- Centro de Biologia Estrutural e Bioimagem, Rio de Janeiro, 21941-920, Brazil; Instituto de Bioquímica Médica, Centro Nacional de Ressonância Magnética Nuclear Jiri Jonas, Universidade Federal do Rio de Janeiro, 21941-920, Brazil.
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Exploiting the antithrombotic effect of the (pro)thrombin inhibitor bothrojaracin. Toxicon 2016; 119:46-51. [PMID: 27179421 DOI: 10.1016/j.toxicon.2016.05.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Revised: 05/04/2016] [Accepted: 05/10/2016] [Indexed: 11/20/2022]
Abstract
Bothrojaracin is a 27 kDa C-type lectin-like protein from Bothrops jararaca snake venom. It behaves as a potent thrombin inhibitor upon high-affinity binding to thrombin exosites. Bothrojaracin also forms a stable complex with prothrombin that can be detected in human plasma. Formation of the zymogen-inhibitor complex severely decreases prothrombin activation and contributes to the anticoagulant activity of bothrojaracin. In the present study, we employed two rodent models to evaluate the antithrombotic effect of bothrojaracin in vivo: stasis-induced thrombosis and thrombin-induced pulmonary thromboembolism. It was observed that bothrojaracin interacts with rat prothrombin in plasma. Ex-vivo assays showed stable complex formation even after 24 h of a single bothrojaracin dose. As a result, bothrojaracin showed significant antithrombotic activity in a rat venous thrombosis model elicited by thromboplastin combined with stasis. The antithrombotic activity of bothrojaracin (1 mg/kg) persisted for up to 24 h and it was associated with moderate bleeding as assessed by a tail transection method. Formation of bothrojaracin-prothrombin complex has been also observed following intravenous administration of the inhibitor into mice. As a result, bothrojaracin effectively protected mice from thrombin-induced fatal thromboembolism. We conclude that bothrojaracin is a potent antithrombotic agent in vivo and may serve as a prototype for the development of new zymogen-directed drugs that could result in prolonged half-life and possible decreased hemorrhagic risk.
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Choi KM, Jeong JM, Bae JS, Cho DH, Jung SH, Hwang JY, Baeck GW, Park CI. Coagulation factor II from rock bream (Oplegnathus fasciatus): First report on the molecular biological function and expression analysis in the teleost. FISH & SHELLFISH IMMUNOLOGY 2016; 48:145-153. [PMID: 26626585 DOI: 10.1016/j.fsi.2015.11.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 11/19/2015] [Accepted: 11/22/2015] [Indexed: 06/05/2023]
Abstract
The rapid haemostasis of fish prevents bleeding or infection that could be caused by physical properties of the aquatic environment. Additionally, the innate immune system is the first line of defence against infection and is responsible for the recognition of pathogen-associated molecular patterns, which are important for the activation of acquired immune responses. Coagulation factor II (CFII) is an important factor in the coagulation system and is involved in recognition and interaction with various bacterial and extracellular proteins. In this study, we identified and characterised the gene encoding CFII in rock bream (Oplegnathus fasciatus) (RbCFII) and analysed its expression in various tissues after a pathogen challenge. The full-length RbCFII cDNA (2079 bp) contained an open reading frame of 1854 bp encoding 617 amino acids. Alignment analysis revealed that a gamma-carboxyglutamic acid-rich domain, two kringle domains, and a trypsin-like serine protease domain of the deduced protein were well conserved. RbCFII was ubiquitously expressed in all tissues examined but, predominantly detected in the liver and skin. RbCFII expression was dramatically up-regulated in the kidney, spleen and liver after infection with Edwardsiella tarda, Streptococcus iniae, or red seabream iridovirus. The recombinant protein RbCFII (rRbCFII) produced using an Escherichia coli expression system was able to bind all examined bacteria. Interestingly, rRbCFII has agglutination activities towards E. coli and E. tarda, while no agglutination was shown toward Vibrio ordalii and S. iniae. These findings indicate that rRbCFII performs an immunological function in the immune response, and might be involved in innate immunity as well as blood coagulation.
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Affiliation(s)
- Kwang-Min Choi
- Department of Marine Biology and Aquaculture, College of Marine Science, Gyeongsang National University, 38 Cheondaegukchi-Gil, Tongyeong, Gyeongnam 650-160, Republic of Korea
| | - Ji-Min Jeong
- Department of Marine Biology and Aquaculture, College of Marine Science, Gyeongsang National University, 38 Cheondaegukchi-Gil, Tongyeong, Gyeongnam 650-160, Republic of Korea
| | - Jin-Sol Bae
- Department of Marine Biology and Aquaculture, College of Marine Science, Gyeongsang National University, 38 Cheondaegukchi-Gil, Tongyeong, Gyeongnam 650-160, Republic of Korea
| | - Dong-Hee Cho
- Department of Marine Biology and Aquaculture, College of Marine Science, Gyeongsang National University, 38 Cheondaegukchi-Gil, Tongyeong, Gyeongnam 650-160, Republic of Korea
| | - Sung Hee Jung
- Pathology Division, National Fisheries Research and Development Institute, Busan 619-900, Republic of Korea
| | - Jee-Youn Hwang
- Pathology Division, National Fisheries Research and Development Institute, Busan 619-900, Republic of Korea
| | - Gun-Wook Baeck
- Department of Marine Biology and Aquaculture, College of Marine Science, Gyeongsang National University, 38 Cheondaegukchi-Gil, Tongyeong, Gyeongnam 650-160, Republic of Korea
| | - Chan-Il Park
- Department of Marine Biology and Aquaculture, College of Marine Science, Gyeongsang National University, 38 Cheondaegukchi-Gil, Tongyeong, Gyeongnam 650-160, Republic of Korea.
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Saviola AJ, Peichoto ME, Mackessy SP. Rear-fanged snake venoms: an untapped source of novel compounds and potential drug leads. TOXIN REV 2014. [DOI: 10.3109/15569543.2014.942040] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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8
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Kroh HK, Bock PE. Effect of zymogen domains and active site occupation on activation of prothrombin by von Willebrand factor-binding protein. J Biol Chem 2012; 287:39149-57. [PMID: 23012355 DOI: 10.1074/jbc.m112.415562] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Prothrombin is conformationally activated by von Willebrand factor-binding protein (vWbp) from Staphylococcus aureus through insertion of the NH(2)-terminal residues of vWbp into the prothrombin catalytic domain. The rate of prothrombin activation by vWbp(1-263) is controlled by a hysteretic kinetic mechanism initiated by substrate binding. The present study evaluates activation of prothrombin by full-length vWbp(1-474) through activity progress curve analysis. Additional interactions from the COOH-terminal half of vWbp(1-474) strengthened the initial binding of vWbp to prothrombin, resulting in higher activity and an ∼100-fold enhancement in affinity. The affinities of vWbp(1-263) or vWbp(1-474) were compared by equilibrium binding to the prothrombin derivatives prethrombin 1, prethrombin 2, thrombin, meizothrombin, and meizothrombin(des-fragment 1) and their corresponding active site-blocked analogs. Loss of fragment 1 in prethrombin 1 enhanced affinity for both vWbp(1-263) and vWbp(1-474), with a 30-45% increase in Gibbs free energy, implicating a regulatory role for fragment 1 in the activation mechanism. Active site labeling of all prothrombin derivatives with D-Phe-Pro-Arg-chloromethyl ketone, analogous to irreversible binding of a substrate, decreased their K(D) values for vWbp into the subnanomolar range, reflecting the dependence of the activating conformational change on substrate binding. The results suggest a role for prothrombin domains in the pathophysiological activation of prothrombin by vWbp, and may reveal a function for autocatalysis of the vWbp·prothrombin complexes during initiation of blood coagulation.
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Affiliation(s)
- Heather K Kroh
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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9
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Carneiro-Lobo TC, Konig S, Machado DE, Nasciutti LE, Forni MF, Francischetti IMB, Sogayar MC, Monteiro RQ. Ixolaris, a tissue factor inhibitor, blocks primary tumor growth and angiogenesis in a glioblastoma model. J Thromb Haemost 2009; 7:1855-64. [PMID: 19624457 PMCID: PMC2896491 DOI: 10.1111/j.1538-7836.2009.03553.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND The expression levels of the clotting initiator protein Tissue Factor (TF) correlate with vessel density and the histological malignancy grade of glioma patients. Increased procoagulant tonus in high grade tumors (glioblastomas) also indicates a potential role for TF in progression of this disease, and suggests that anticoagulants could be used as adjuvants for its treatment. OBJECTIVES We hypothesized that blocking of TF activity with the tick anticoagulant Ixolaris might interfere with glioblastoma progression. METHODS AND RESULTS TF was identified in U87-MG cells by flow-cytometric and functional assays (extrinsic tenase). In addition, flow-cytometric analysis demonstrated the exposure of phosphatidylserine in the surface of U87-MG cells, which supported the assembly of intrinsic tenase (FIXa/FVIIIa/FX) and prothrombinase (FVa/FXa/prothrombin) complexes, accounting for the production of FXa and thrombin, respectively. Ixolaris effectively blocked the in vitro TF-dependent procoagulant activity of the U87-MG human glioblastoma cell line and attenuated multimolecular coagulation complexes assembly. Notably, Ixolaris inhibited the in vivo tumorigenic potential of U87-MG cells in nude mice, without observable bleeding. This inhibitory effect of Ixolaris on tumor growth was associated with downregulation of VEGF and reduced tumor vascularization. CONCLUSION Our results suggest that Ixolaris might be a promising agent for anti-tumor therapy in humans.
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Affiliation(s)
- T C Carneiro-Lobo
- Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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10
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Ribeiro MMB, Franquelim HG, Castanho MARB, Veiga AS. Molecular interaction studies of peptides using steady-state fluorescence intensity. Static (de)quenching revisited. J Pept Sci 2008; 14:401-6. [PMID: 17994617 DOI: 10.1002/psc.939] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Protein-protein interactions, as well as peptide-peptide and peptide-protein interactions are fields of study of growing importance as molecular-level detail is avidly pursued in drug design, metabolic regulation and molecular dynamics, among other classes of studies. In membranes, this issue is particularly relevant because lipid bilayers potentiate molecular interactions due to the high local concentration of peptides and other solutes.However, experimental techniques and methodologies to detect and quantify such interactions are not abundant. A reliable, fast and inexpensive alternative methodology is revisited in this work. Considering the interaction of two molecules, at least one of them being fluorescent, either intrinsically (e.g. Trp residues) or by grafting a specific probe, changes in their aggregation state may be reported, as long as the fluorophore is sensitive to local changes in polarity, conformation and/or exposure to the solvent. The interaction will probably lead to modifications in fluorescence intensity resulting in a decrease ('quenching') or enhancement ('dequenching'). Although the presented methodology is based on static quenching methodologies, the concept is extended from quenching to any kind of interference with the fluorophore. Equations for data analysis are shown and their applications are illustrated by calculating the binding constant for several data-sets.
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Affiliation(s)
- Marta M B Ribeiro
- Centro de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, Ed C8, 1749-016 Lisboa, Portugal
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11
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Melo FR, Pereira MS, Monteiro RQ, Foguel D, Mourão PAS. Sulfated galactan is a catalyst of antithrombin-mediated inactivation of alpha-thrombin. Biochim Biophys Acta Gen Subj 2008; 1780:1047-53. [PMID: 18558097 DOI: 10.1016/j.bbagen.2008.05.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2008] [Revised: 05/20/2008] [Accepted: 05/20/2008] [Indexed: 11/16/2022]
Abstract
Novel compounds presenting anticoagulant activity, such as sulfated polysaccharides, open new perspectives in medicine. Elucidation of the molecular mechanism behind this activity is desirable by itself, as well as because it allows for the design of novel compounds. In the present study, we investigated the action of an algal sulfated galactan, which potentiates alpha-thrombin inactivation by antithrombin. Our results indicate the following: 1) both the sulfated galactan and heparin potentiate protease inactivation by antithrombin at similar molar concentrations, however they differ markedly in the molecular size required for their activities; 2) this galactan interacts predominantly with exosite II on alpha-thrombin and, similar to heparin, catalyzes the formation of a covalent complex between antithrombin and the protease; 3) the sulfated galactan has a higher affinity for alpha-thrombin than for antithrombin. We propose that the preferred pathway of sulfated galactan-induced inactivation of alpha-thrombin by antithrombin starts with the polysaccharide binding to the protease through a high-affinity interaction. Antithrombin is then added to the complex and the protease is inactivated by covalent interactions. Finally, the antithrombin-alpha-thrombin covalent complex dissociates from the polysaccharide chain. This mechanism resembles the action of heparin with low affinity for antithrombin, as opposed to heparin with high affinity for serpin.
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Affiliation(s)
- Fábio R Melo
- Laboratório de Tecido Conjuntivo, Hospital Universitário Clementino Fraga Filho, Universidade Federal do Rio de Janeiro, Caixa Postal 68041, Rio de Janeiro, RJ, 21941-590, Brazil
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12
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Monteiro RQ, Rezaie AR, Bae JS, Calvo E, Andersen JF, Francischetti IMB. Ixolaris binding to factor X reveals a precursor state of factor Xa heparin-binding exosite. Protein Sci 2007; 17:146-53. [PMID: 18042685 DOI: 10.1110/ps.073016308] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Ixolaris is a two-Kunitz tick salivary gland tissue factor pathway inhibitor (TFPI). In contrast to human TFPI, Ixolaris specifically binds to factor Xa (FXa) heparin-binding exosite (HBE). In addition, Ixolaris interacts with zymogen FX. In the present work we characterized the interaction of Ixolaris with human FX quantitatively, and identified a precursor state of the heparin-binding exosite (proexosite, HBPE) as the Ixolaris-binding site on the zymogen. Gel-filtration chromatography demonstrated 1:1 complex formation between fluorescein-labeled Ixolaris and FX. Isothermal titration calorimetry confirmed that the binding of Ixolaris to FX occurs at stoichiometric concentrations in a reaction which is characteristically exothermic, with a favorable enthalpy (DeltaH) of -10.78 kcal/mol. ELISA and plasmon resonance experiments also indicate that Ixolaris binds to plasma FX and FXa, or to recombinant Gla domain-containing FX/FXa with comparable affinities ( approximately 1 nM). Using a series of mutants on the HBPE, we identified the most important amino acids involved in zymogen/Ixolaris interaction-Arg-93 >>> Arg-165 > or = Lys-169 > Lys-236 > Arg-125-which was identical to that observed for FXa/Ixolaris interaction. Remarkably, Ixolaris strongly inhibited FX activation by factor IXa in the presence but not in the absence of factor VIIIa, suggesting a specific interference in the cofactor activity. Further, solid phase assays demonstrated that Ixolaris inhibits FX interaction with immobilized FVIIIa. Altogether, Ixolaris is the first inhibitor characterized to date that specifically binds to FX HBPE. Ixolaris may be a useful tool to study the physiological role of the FX HBPE and to evaluate this domain as a target for anticoagulant drugs.
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Affiliation(s)
- Robson Q Monteiro
- Instituto de Bioquimica Medica, Centro de Ciencias de Saude, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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13
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Mariano-Oliveira A, De Freitas MS, Monteiro RQ, Barja-Fidalgo C. Prothrombin fragments containing kringle domains induce migration and activation of human neutrophils. Int J Biochem Cell Biol 2007; 40:517-29. [PMID: 17951099 DOI: 10.1016/j.biocel.2007.09.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2007] [Revised: 08/29/2007] [Accepted: 09/03/2007] [Indexed: 11/16/2022]
Abstract
The cross-talk between inflammatory and coagulation cascades has been demonstrated. Prothrombin processing releases the protease domain (thrombin) along with two catalytically inactive kringle-containing derivatives: prothrombin fragments 1 (F1) and 2 (F2). It is well established that thrombin is able to trigger an inflammatory response but the possible effects of prothrombin fragments on leukocyte functions are still unknown. In this report, we demonstrate for the first time that both F1 and F2 prothrombin fragments, interfere with intracellular functional signaling pathways to modulate human neutrophil migration. In addition, we show that thrombin, fragment 1 and fragment 2 induce human neutrophil chemotaxis. The effect of fragment 2, but not fragment 1, was partially inhibited by pertussis toxin, an inhibitor of G(alphai)-signaling. The pre-treatment of cells with fragment 2 inhibited thrombin-induced chemotaxis, while both fragments impaired neutrophil migration induced by interleukin-8. F1 and F2 increased the expression and activation of G-protein-coupled receptor kinase-2, which has emerged as a key effector in the desensitization of chemokine receptors. In parallel, prothrombin fragments activated extracellular signal-regulated kinase 1/2, stimulating its phosphorylation and nuclear translocation, and induced inhibitor of kappa-B phosphorylation and degradation followed by nuclear factor-kappa B translocation to nucleus. Furthermore, both prothrombin fragments induced interleukin-8 gene expression in human neutrophils. These findings suggest that the interference with neutrophil signaling and function, caused by kringle-containing prothrombin fragments may desensitize these cells to respond to further activation by thrombin and interleukin-8 during inflammatory and coagulation responses.
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Affiliation(s)
- Andréa Mariano-Oliveira
- Departamento de Farmacologia, Instituto de Biologia, Universidade do Estado do Rio de Janeiro, Av. 28 de setembro 87 fds, Vila Isabel, Rio de Janeiro, 20551-030 RJ, Brazil
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14
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Abstract
The specificity of blood coagulation proteinases for substrate, inhibitor, and effector recognition is mediated by exosites on the surfaces of the catalytic domains, physically separated from the catalytic site. Some thrombin ligands bind specifically to either exosite I or II, while others engage both exosites. The involvement of different, overlapping constellations of exosite residues enables binding of structurally diverse ligands. The flexibility of the thrombin structure is central to the mechanism of complex formation and the specificity of exosite interactions. Encounter complex formation is driven by electrostatic ligand-exosite interactions, followed by conformational rearrangement to a stable complex. Exosites on some zymogens are in low affinity proexosite states and are expressed concomitant with catalytic site activation. The requirement for exosite expression controls the specificity of assembly of catalytic complexes on the coagulation pathway, such as the membrane-bound factor Xa*factor Va (prothrombinase) complex, and prevents premature assembly. Substrate recognition by prothrombinase involves a two-step mechanism with initial docking of prothrombin to exosites, followed by a conformational change to engage the FXa catalytic site. Prothrombin and its activation intermediates bind prothrombinase in two alternative conformations determined by the zymogen to proteinase transition that are hypothesized to involve prothrombin (pro)exosite I interactions with FVa, which underpin the sequential activation pathway. The role of exosites as the major source of substrate specificity has stimulated development of exosite-targeted anticoagulants for treatment of thrombosis.
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Affiliation(s)
- P E Bock
- Department of Pathology, Vanderbilt University, Nashville, TN 37232-2561, USA.
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Abstract
Over the last several decades, research on snake venom toxins has provided not only new tools to decipher molecular details of various physiological processes, but also inspiration to design and develop a number of therapeutic agents. Blood circulation, particularly thrombosis and haemostasis, is one of the major targets of several snake venom proteins. Among them, anticoagulant proteins have contributed to our understanding of molecular mechanisms of blood coagulation and have provided potential new leads for the development of drugs to treat or to prevent unwanted clot formation. Some of these anticoagulants exhibit various enzymatic activities whereas others do not. They interfere in normal blood coagulation by different mechanisms. Although significant progress has been made in understanding the structure-function relationships and the mechanisms of some of these anticoagulants, there are still a number of questions to be answered as more new anticoagulants are being discovered. Such studies contribute to our fight against unwanted clot formation, which leads to death and debilitation in cardiac arrest and stroke in patients with cardiovascular and cerebrovascular diseases, arteriosclerosis and hypertension. This review describes the details of the structure, mechanism and structure-function relationships of anticoagulant proteins from snake venoms.
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Affiliation(s)
- R Manjunatha Kini
- Protein Science Laboratory, Department of Biological Sciences, Faculty of Science, National University of Singapore, 14 Science Drive 4, Singapore.
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16
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Zingali RB, Ferreira MS, Assafim M, Frattani FS, Monteiro RQ. Bothrojaracin, a Bothrops jararaca Snake Venom-Derived (Pro)Thrombin Inhibitor, as an Anti-Thrombotic Molecule. PATHOPHYSIOLOGY OF HAEMOSTASIS AND THROMBOSIS 2006; 34:160-3. [PMID: 16707920 DOI: 10.1159/000092416] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Bothrojaracin (BJC) is a selective and potent thrombin inhibitor (KD = 0.6 nM) which also binds to prothrombin on proexosite I (KD = 175 nM). Incubation of BJC with human or rat plasma produced a band that co-migrates with purified prothrombin-BJC complex. We further analyzed the in vivo anti-thrombotic effect of BJC on a venous thrombosis model in rats that combines stasis and hypercoagulability. The administration of 1 mg/kg (i.v.) doses of BJC decreased thrombus weight by approximately 95%. Evaluation of the in vivo effect of BJC in mice using a pulmonary thromboembolism model induced by thrombin showed that BJC protects 100% of mice from death. Altogether, our data show that BJC is a potent anti-thrombotic agent that could further help the development of new prothrombin-directed drugs.
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Affiliation(s)
- Russolina B Zingali
- Instituto de Bioquímica Médica, CCS, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
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17
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Castro HC, Monteiro RQ, Assafim M, Loureiro NIV, Craik C, Zingali RB. Ecotin modulates thrombin activity through exosite-2 interactions. Int J Biochem Cell Biol 2006; 38:1893-900. [PMID: 16843700 DOI: 10.1016/j.biocel.2006.05.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2005] [Revised: 04/09/2006] [Accepted: 05/10/2006] [Indexed: 10/24/2022]
Abstract
Ecotin is a Escherichia coli-derived protein that has been characterized as a potent inhibitor of serine-proteases. This protein is highly effective against several mammalian enzymes, which includes pancreatic and neutrophil-derived elastases, chymotrypsin, trypsin, factor Xa, and kallikrein. In this work we showed that ecotin binds to human alpha-thrombin via its secondary binding site, and modulates thrombin catalytic activity. Formation of wild type ecotin-alpha-thrombin complex was observed by native PAGE and remarkably, gel filtration chromatography showed an unusual 2:1 ecotin:enzyme stoichiometry. Analysis of the protease inhibitor effects on thrombin biological activities showed that (i) it decreases the inhibition of thrombin by heparin/antithrombin complex (IC50=3.2 microM); (ii) it produces a two-fold increase in the thrombin-induced fibrinogen clotting; and (iii) it inhibits thrombin-induced platelet aggregation (IC50=4.5 microM). Allosteric changes on thrombin structure were then evaluated. Complex formation with ecotin caused a three-fold increase in the rate of thrombin inhibition by BPTI, suggesting a displacement of the enzyme's 60-loop. In addition, ecotin modulated the enzyme's catalytic site, as demonstrated by changes in the fluorescence emission of fluorescein-FPRCK-alpha-thrombin (EC50=3.5 microM). Finally, solid phase competition assays demonstrated that heparin and prothrombin fragment 2 prevents thrombin interaction with ecotin. Altogether, these observations strongly support an ecotin interaction with thrombin anion-binding exosite-2, resulting in modulation of its biological activities. At this point, ecotin might be useful as a new tool for studying thrombin allosteric modulation.
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Affiliation(s)
- Helena C Castro
- LaBioMol, Departamento de Biologia Celular e Molecular, Instituto de Biologia, Universidade Federal Fluminense, Outeiro São João Batista, Niterói, RJ 24001-970, Brazil
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18
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Lu Q, Navdaev A, Clemetson JM, Clemetson KJ. Snake venom C-type lectins interacting with platelet receptors. Structure–function relationships and effects on haemostasis. Toxicon 2005; 45:1089-98. [PMID: 15876445 DOI: 10.1016/j.toxicon.2005.02.022] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/23/2004] [Indexed: 11/16/2022]
Abstract
Snake venoms contain components that affect the prey either by neurotoxic or haemorrhagic effects. The latter category affect haemostasis either by inhibiting or activating platelets or coagulation factors. They fall into several types based upon structure and mode of action. A major class is the snake C-type lectins or C-type lectin-like family which shows a typical folding like that in classic C-type lectins such as the selectins and mannose-binding proteins. Those in snake venoms are mostly based on a heterodimeric structure with two subunits alpha and beta, which are often oligomerized to form larger molecules. Simple heterodimeric members of this family have been shown to inhibit platelet functions by binding to GPIb but others activate platelets via the same receptor. Some that act via GPIb do so by inducing von Willebrand factor to bind to it. Another series of snake C-type lectins activate platelets by binding to GPVI while yet another series uses the integrin alpha(2)beta(1) to affect platelet function. The structure of more and more of these C-type lectins have now been, and are being, determined, often together with their ligands, casting light on binding sites and mechanisms. In addition, it is relatively easy to model the structure of the C-type lectins if the primary structure is known. These studies have shown that these proteins are quite a complex group, often with more than one platelet receptor as ligand and although superficially some appear to act as inhibitors, in fact most function by inducing thrombocytopenia by various routes. The relationship between structure and function in this group of venom proteins will be discussed.
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Affiliation(s)
- Qiumin Lu
- Theodor Kocher Institute, University of Berne, Freiestrasse 1, CH-3012, Berne, Switzerland
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19
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Abstract
The high specificity of blood coagulation proteases has been attributed not only to residues surrounding the active site but also to other surface domains that are involved in recognizing and interacting with macromolecular substrates and inhibitors. Specific blood coagulation inhibitors obtained from exogenous sources such as blood sucking salivary glands and snake venoms have been identified. Some of these inhibitors interact with exosites on coagulation enzymes. Two examples are discussed in this short revision. Bothrojaracin is a snake venom-derived protein that binds to thrombin exosites 1 and 2. Complex formation impairs several exosite-dependent activities of thrombin including fibrinogen cleavage and platelet activation. Bothrojaracin also interacts with proexosite 1 on prothrombin thus decreasing the zymogen activation by the prothrombinase complex (FXa/FVa). Ixolaris is a two Kunitz tick salivary gland inhibitor, that is homologous to tissue factor pathway inhibitor. Recently it was demonstrated that ixolaris binds to heparin-binding exosite of FXa, thus impairing the recognition of prothrombin by the enzyme. In addition, ixolaris interacts with FX possibly through the heparin-binding proexosite. Differently from FX, the ixolaris-FX complex is not recognized as substrate by the intrinsic tenase complex (FIXa/FVIIIa). We conclude that these inhibitors may serve as tools for the study of coagulation exosites as well as prototypes for new anticoagulant drugs.
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Affiliation(s)
- Robson Q Monteiro
- Laboratório de Hemostase e Venenos, Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-590, Brasil.
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Kirszberg C, Rumjanek VM, Monteiro RQ. Assembly and regulation of prothrombinase complex on B16F10 melanoma cells. Thromb Res 2005; 115:123-9. [PMID: 15567463 DOI: 10.1016/j.thromres.2004.08.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2004] [Revised: 07/30/2004] [Accepted: 08/04/2004] [Indexed: 11/16/2022]
Abstract
A number of studies indicate that coagulation proteases play significant roles in cancer biology. Melanoma is a highly metastatic cancer, and there is evidence that thrombin contributes to this aggressive pattern. However, few studies correlate this type of cancer with formation of the prothrombinase complex, which is responsible for conversion of prothrombin into thrombin in the coagulation system. The aim of this study was to investigate the assembly and regulation of prothrombinase complex on the murine melanoma cell line, B16F10. B16F10 cells were unable to activate prothrombin except when previously incubated with factor Xa. This effect was dependent on factor Xa binding to cell membranes, since no activation was detected with Gla-domainless factor Xa. The thrombin formation by B16F10-bound factor Xa was enhanced approximately 10 fold in the presence of factor Va, indicating the assembly of prothrombinase complex. Differently from platelets, B16F10-assembled prothrombinase complex was inhibited by prothrombin fragment 1 but not by fragment 2. In addition, bothrojaracin, a specific ligand of proexosite I on prothrombin, caused a significant decrease in the zymogen activation. Our data demonstrate that B16F10 melanoma cells generate thrombin by promoting assembly of the prothrombinase complex. This ability might be correlated with the increased metastatic potential of this cell line. Moreover, B16F10-assembled prothrombinase complex seems to be modulated in a different way from that found for the physiological complex assembled on platelets.
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Affiliation(s)
- Clarice Kirszberg
- Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Avenida Bauhínia 400, Rio de Janeiro, CEP-21941-590, Rio de Janeiro, Brazil
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Anderson PJ, Nesset A, Bock PE. Effects of activation peptide bond cleavage and fragment 2 interactions on the pathway of exosite I expression during activation of human prethrombin 1 to thrombin. J Biol Chem 2003; 278:44482-8. [PMID: 12939269 DOI: 10.1074/jbc.m306917200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of prothrombin (Pro) by factor Xa to form thrombin occurs by proteolysis of Arg271-Thr272 and Arg320-Ile321, resulting in expression of regulatory exosites I and II. Cleavage of Pro by thrombin liberates fragment 1 and generates the zymogen analog, prethrombin 1 (Pre 1). The properties of exosite I on Pre 1 and its factor Xa activation intermediates were characterized in spectroscopic and equilibrium binding studies using the fluorescein-labeled probe, hirudin(54-65) ([5F]Hir(54-65)-(SO3-)). Prethrombin 2 (Pre 2), formed by factor Xa cleavage of Pre 1 at Arg271-Thr272, had the same affinity for hirudin(54-65) peptides as Pre 1 in the absence or presence of near-saturating fragment 2 (F2). Pre 2 and thrombin also had indistinguishable affinities for F2. By contrast, cleavage of Pre 1 at Arg320-Ile321, to form active meizothrombin des-fragment 1 MzT(-F1), showed a 11- to 20-fold increase in affinity for hirudin(54-65), indistinguishable from the 13- to 20-fold increase seen for conversion of Pre 2 to thrombin. Thus, factor Xa cleavage of Pre 1 at Arg271-Thr272 does not effect exosite I expression, whereas cleavage at Arg320-Ile321 results in concomitant activation of the catalytic site and exosite I. Furthermore, expression of exosite I on the Pre 1 activation intermediates is not modulated by F2, and exosite II is not activated conformationally. The differential expression of exosite I affinity on the Pre 1 activation intermediates and the previously demonstrated role of (pro)exosite I in factor Va-dependent substrate recognition suggest that changes in exosite I expression may regulate the rate and direction of the Pre 1 activation pathway.
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Affiliation(s)
- Patricia J Anderson
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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Anderson PJ, Bock PE. Role of prothrombin fragment 1 in the pathway of regulatory exosite I formation during conversion of human prothrombin to thrombin. J Biol Chem 2003; 278:44489-95. [PMID: 12939270 DOI: 10.1074/jbc.m306916200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Prothrombin (Pro) activation by factor Xa generates the thrombin catalytic site and exosites I and II. The role of fragment 1 (F1) in the pathway of exosite I expression during Pro activation was characterized in equilibrium binding studies using hirudin(54-65) labeled with 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoate ([NBD]Hir(54-65)(SO3-)) or 5-(carboxy)fluorescein ([5F]Hir(54-65)(SO3-)). [NBD]Hir(54-65)(SO3-) distinguished exosite I environments on Pro, prethrombin 1 (Pre 1), and prethrombin 2 (Pre 2) but bound with the same affinities as [5F]Hir(54-65)(SO3-). Conversion of Pro to Pre 1 caused a 7-fold increase in affinity for the peptides. Conversely, fragment 1.2 (F1.2) decreased the affinity of Pre 2 for [5F]Hir(54-65)(SO3-) by 3-fold. This was correlated with a 16-fold increased affinity of F1.2 for Pre 2 in comparison to thrombin, demonstrating an enhancing effect of F1 on F1.2 binding. The active intermediate, meizothrombin, demonstrated a 50- to 220-fold increase in exosite affinity. Free thrombin and thrombin.F1.2 complex bound [5F]Hir(54-65)(SO3-) with indistinguishable affinity, indicating that the effect of F1 on peptide binding was eliminated upon expression of catalytic activity and exosite I. The results demonstrate a new zymogen-specific role for F1 in modulating the affinity of ligands for exosite I. This may reflect a direct interaction between the F1 and Pre 2 domains in Pro that is lost upon folding of the zymogen activation domain. The effect of F1 on (pro)exosite I and the role of (pro)exosite I in factor Va-dependent substrate recognition suggest that the Pro activation pathway may be regulated by (pro)exosite I interactions with factor Va.
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Affiliation(s)
- Patricia J Anderson
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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Tolkatchev D, Xu P, Ni F. Probing the Kinetic Landscape of Transient Peptide−Protein Interactions by Use of Peptide 15N NMR Relaxation Dispersion Spectroscopy: Binding of an Antithrombin Peptide to Human Prothrombin. J Am Chem Soc 2003; 125:12432-42. [PMID: 14531686 DOI: 10.1021/ja021238l] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Protein-ligand interactions may lead to the formation of multiple molecular complexes in dynamic exchange, affecting the kinetic and thermodynamic characteristics of the binding equilibrium. We followed the dissociation kinetics of the transient and specific complex of an antithrombotic peptide N-acetyl-Asp(55)-Phe-Glu-Glu-Ile-Pro(60)-Glu-Glu-Tyr-Leu-Gln(65) with human prothrombin by use of (15)N NMR relaxation dispersion spectroscopy of the peptide. Every one of the five (15)N-labeled adjacent residues of the peptide exhibited apparently different kinetic exchange and relaxation behaviors, which were especially evident at different concentrations of prothrombin. Binding-induced (15)N relaxation dispersion of residues Phe(56), Glu(57), Glu(58), and Ile(59) can be fitted phenomenologically to a two-site on-and-off exchange mechanism with physically feasible relaxation and kinetic parameters obtained for residues Phe(56), Glu(58), and Ile(59), independent of the prothrombin concentration. The apparent kinetic parameters of Glu(57) show some dependence on the concentration of prothrombin and the extracted transverse relaxation rate for Glu(57) in the bound state was severalfold higher than that expected for a protein-peptide complex with a size of approximately 72 kDa. In addition, the equilibrium population of the bound peptide obtained for Glu(57) was inconsistent with those for Phe(56), Glu(58), and Ile(59) and with the prothrombin/peptide ratios used in the experiments. These discrepancies can be explained by the presence of two conformations for the peptide-protein complex exchanging at a rate of approximately 100 s(-)(1). In all, our study shows that fast dissociation of protein-peptide complexes can be studied quantitatively using peptide (15)N NMR relaxation dispersion measurements without a precise knowledge of the peptide and protein concentrations. In addition, protein titration was found to improve the accuracy of quantitative analysis and may make it possible to determine the rate of conformational changes within the protein-peptide complex.
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Affiliation(s)
- Dmitri Tolkatchev
- Biomolecular NMR and Protein Research Laboratory, Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec, Canada H4P 2R2
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Zingali RB, Bianconi ML, Monteiro RQ. Interaction of bothrojaracin with prothrombin. HAEMOSTASIS 2001; 31:273-8. [PMID: 11910195 DOI: 10.1159/000048073] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Bothrojaracin (BJC) is a 27-kD protein from Bothrops jararaca venom that interacts with alpha-thrombin (K(D) = 0.7 nM) through both anion-binding exosites I and II. Recently, it has been shown that BJC interacts with the exosite I precursor (proexosite I) on human prothrombin (K(D) = 75 nM), forming a 1:1 Ca(2+)-independent noncovalent complex with the zymogen. Complex formation was associated with inhibition of zymogen activation by Oxyuranus scutellatus venom. In addition, BJC strongly decreased the prothrombin activation by factor Xa only in the presence of factor Va. A similar effect was observed in the presence of phospholipids, suggesting that BJC specifically inhibits the interaction of prothrombin with factor Va. It is proposed that BJC has two independent mechanisms for anticoagulation: (1) inhibition of exosite-I-dependent activities on alpha-thrombin, and (2) inhibition of prothrombin activation through interaction with proexosite I.
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Affiliation(s)
- R B Zingali
- Departamento de Bioquímica Médica/ICB/CCS, Bloco H-2o Andar-Ilha do Fundao, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-590, Brazil.
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