Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: HUMANGGP:027518 (factor Xa)
 5,167 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Factor X is activated to factor Xa (fXa) in the extrinsic coagulation pathway by the tissue factor (TF)/factor VIIa (fVIIa) complex. Upon activation, the fXa molecule remains associated with the TF/fVIIa complex, and this ternary complex is known to activate protease-activated receptors (PARs) 1 and 2. Activation of fVII in the TF complex by fXa is also seen at physiologic concentrations. The ternary complexes TF/fVII/fXa, TF/fVIIa/fX, and TF/fVIIa/fXa are therefore all physiologically relevant and of interest as targets for inhibition of both coagulation and cell-signaling pathways that are important in cardiovascular disease and inflammation. We therefore present a model of the TF/fVIIa/fXa complex, built with the use of the available structures of the TF/fVIIa complex and fXa by protein-protein docking calculations with the program Surfdock. The fXa model has an extended conformation, similar to that of fVIIa in the TF/fVIIa complex, with extensive interactions with TF and the protease domain of fVIIa. All four domains of fXa are involved in the interaction. The gamma-carboxyglutamate (Gla) and epithelial growth factor (EGF1 and EGF2) domains of fVIIa are not significantly involved in the interaction. Docking of the Gla domain of fXa to TF/fVIIa has been reported previously. The docking results identify potential interface residues, allowing rational selection of target residues for site-directed mutagenesis. This combination of docking and mutagenesis confirms that residues Glu51 and Asn57 in the EGF1 domain, Asp92 and Asp95 in the EGF2 domain, and Asp 185a, Lys 186, and Lys134 in the protease domain of factor Xa are involved in the interaction with TF/fVIIa. Other fX protease domain residues predicted to be involved in the interaction come from the 160s loop and the N-terminus of the fX protease domain, which is oriented in such a way that activation of both fVII by fXa, and the reciprocal fX activation by fVIIa, is possible.
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PMID:The tissue factor/factor VIIa/factor Xa complex: a model built by docking and site-directed mutagenesis. 1457 55

The S1 site (Asp(189)) of factor Xa (fXa) is located on a loop (residues 185-189) that contains three solvent-exposed charged residues (Asp(185), Lys(186), and Glu(188)) below the active-site pocket of the protease. To investigate the role of these residues in the catalytic function of fXa, we expressed three mutants of the protease in which the charges of these residues were neutralized by their substitutions with Ala (D185A, K186A, and E188A). Kinetic studies revealed that E188A has a normal catalytic activity toward small synthetic and natural substrates and inhibitors of fXa; however, the same activities were slightly ( approximately 2-fold) and dramatically ( approximately 20-50-fold) impaired for the D185A and K186A mutants, respectively. Further studies revealed that the affinity of D185A and K186A for interaction with Na(+) has also been altered, with a modest impairment ( approximately 2-fold) for the former and a dramatic impairment for the latter mutant. Both prothrombinase and direct binding studies indicated that K186A also has an approximately 6-fold impaired affinity for factor Va. Interestingly, a saturating concentration of factor Va restored the catalytic defect of K186A in reactions with prothrombin and the recombinant tick anticoagulant peptide that is known to interact with the Na(+) loop of fXa, but not with other substrates. These results suggest that factor Va interacts with 185-189-loop for fXa, which is energetically linked to the Na(+)-binding site of the protease.
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PMID:The critical role of the 185-189-loop in the factor Xa interaction with Na+ and factor Va in the prothrombinase complex. 1534 60

It has been hypothesized that two antiparallel structures comprised of residues 82-91 and 102-116 in factor Xa (fXa) may harbor a factor Va- (fVa-) dependent prothrombin recognition site in the prothrombinase complex. There are 11 charged residues in the 82-116 loop of human fXa (Glu-84, Glu-86, Lys-90, Arg-93, Lys-96, Glu-97, Asp-100, Asp-102, Arg-107, Lys-109, and Arg-115). With the exception of Glu-84, which did not express, and Asp-102, which is a catalytic residue, we expressed the Ala substitution mutants of all other residues and evaluated their proteolytic and amidolytic activities in both the absence and presence of fVa. K96A and K109A activated prothrombin with 5-10-fold impaired catalytic efficiency in the absence of fVa. All mutants, however, exhibited normal activity toward the substrate in the presence of fVa. K109A also exhibited impaired amidolytic activity and affinity for Na(+); however, both fVa and higher Na(+) restored the catalytic defect caused by the mutation. Analysis of the X-ray crystal structure of fXa indicated that Glu-84 may interact by a salt bridge with Lys-109, explaining the lack of expression of E84A and the lower activity of K109A in the absence of fVa. These results suggest that none of the residues under study is a fVa-dependent recognition site for prothrombin in the prothrombinase complex; however, Lys-96 is a recognition site for the substrate independent of the cofactor. Moreover, the 82-116 loop is energetically linked to fVa and Na(+) binding sites of the protease.
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PMID:Functional mapping of charged residues of the 82-116 sequence in factor Xa: evidence that lysine 96 is a factor Va independent recognition site for prothrombin in the prothrombinase complex. 1604 83

Wild-type and an active site mutant (S25T) human foamy virus (HFV) proteases were expressed in fusion with maltose binding protein in Escherichia coli. The mutant enzyme contained a Ser to Thr mutation in the -Asp-Ser-Gly- active site triplet of the enzyme, which forms the "fireman's grip" between the two subunits of the homodimeric enzyme. The fusion proteins were purified by affinity chromatography on amylose resin, cleaved with factor Xa, and the processed enzymes were purified by gel filtration under denaturing condition. Refolding after purification resulted in active enzymes with comparable yields. Furthermore, both enzymes showed similar catalytic activities in an oligopeptide substrate representing an HFV Gag cleavage site. However, the S25T mutant showed increased stability in urea unfolding experiment, in a good agreement with the suggested role of the Thr residue of fireman's grip.
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PMID:Improved purification protocol for wild-type and mutant human foamy virus proteases. 1624 39

Tabanus anticoagulant protein (TAP) was isolated from the whole body of the tabanus, Tabanus bivittatus, using three purification steps (ammonium sulfate fractionation, gel filtration on Bio-Gel P-60, and ion exchange chromatography on DEAE Sephadex gel). The purified TAP, with a molecular weight of 65 kDa, was assessed to be homogeneous by SDS-polyacrylamide gel electrophoresis, and an isoelectric point of 7.9 was determined by isoelectric focusing. The internal amino acid sequence of the purified protein was composed of Ser-Leu-Asn-Asn-Gln-Phe-Ala-Ser-Phe-Ile-Asp-Lys-Val-Arg. The protein was activated by Cu2+ and Zn2+, and the optimal conditions were found to be at pH 3-6 and 40-70 degrees C. Standard coagulation screen assays were used to determine thrombin time and activated partial thromboplastin time. Chromogenic substrate assays were performed for thrombin and factor Xa activity. TAP considerably prolonged human plasma clotting time, especially activated partial thromboplastin time in a dose-dependent manner; it showed potent and specific antithrombin activity in the chromogenic substrate assay. Specific anti-factor Xa activity in TAP was not detected. Overall, this result suggested that TAP has significant anticoagulant activity on blood coagulation system.
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PMID:Purification and characterization of anticoagulant protein from the tabanus, Tabanus bivittatus. 1675 88

Ceramide plays a crucial role as a basic building block of sphingolipids, but also as a signalling molecule mediating cell-fate decisions. Three genes, LAG1, LAC1 and LIP1, have been shown to be required for ceramide synthase activity in Saccharomyces cerevisiae [Guillas, Kirchman, Chuard, Pfefferli, Jiang, Jazwinski and Conzelman (2001) EMBO J. 20, 2655-2665; Schorling, Vallee, Barz, Reizman and Oesterhelt (2001) Mol. Biol. Cell 12, 3417-3427; Vallee and Riezman (2005) EMBO J. 24, 730-741]. In the present study, the topology of the Lag1p and Lac1p subunits was investigated. The N- and C-termini of the proteins are in the cytoplasm and eight putative membrane-spanning domains were identified in Lag1p and Lac1p by insertion of glycosylation and factor Xa cleavage sites at various positions. The conserved Lag motif, potentially containing the active site, is most likely embedded in the membrane. We also present evidence that histidine and aspartic acid residues in the Lag motif are essential for the function of Lag1p in vivo.
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PMID:Transmembrane topology of ceramide synthase in yeast. 1675 12

Membrane-bound factor Xa alone catalyzes prothrombin activation following initial cleavage at Arg(271) and prethrombin 2 formation (pre2 pathway). Factor Va directs prothrombin activation by factor Xa through the meizothrombin pathway, characterized by initial cleavage at Arg(320) (meizo pathway). We have shown previously that a pentapeptide encompassing amino acid sequence 695-699 from the COOH terminus of the heavy chain of factor Va (Asp-Tyr-Asp-Tyr-Gln, DYDYQ) inhibits prothrombin activation by prothrombinase in a competitive manner with respect to substrate. To understand the mechanism of inhibition of thrombin formation by DYDYQ, we have studied prothrombin activation by gel electrophoresis. Titration of plasma-derived prothrombin activation by prothrombinase, with increasing concentrations of peptide, resulted in complete inhibition of the meizo pathway. However, thrombin formation still occurred through the pre2 pathway. These data demonstrate that the peptide preferentially inhibits initial cleavage of prothrombin by prothrombinase at Arg(320). These findings were corroborated by studying the activation of recombinant mutant prothrombin molecules rMZ-II (R155A/R284A/R271A) and rP2-II (R155A/R284A/R320A) which can be only cleaved at Arg(320) and Arg(271), respectively. Cleavage of rMZ-II by prothrombinase was completely inhibited by low concentrations of DYDYQ, whereas high concentrations of pentapeptide were required to inhibit cleavage of rP2-II. The pentapeptide also interfered with prothrombin cleavage by membrane-bound factor Xa alone in the absence of factor Va increasing the rate for cleavage at Arg(271) of plasma-derived prothrombin or rP2-II. Our data demonstrate that pentapeptide DYDYQ has opposing effects on membrane-bound factor Xa for prothrombin cleavage, depending on the incorporation of factor Va in prothrombinase.
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PMID:A control switch for prothrombinase: characterization of a hirudin-like pentapeptide from the COOH terminus of factor Va heavy chain that regulates the rate and pathway for prothrombin activation. 1702 Aug 86

Peptidomimetics have found wide application as bioavailable, biostable, and potent mimetics of naturally occurring biologically active peptides. L-Arginine is a guanidino group-containing basic amino acid, which is positively charged at neutral pH and is involved in many important physiological and pathophysiological processes. Many enzymes display a preference for the arginine residue that is found in many natural substrates and in synthetic inhibitors of many trypsin-like serine proteases, e.g. thrombin, factor Xa, factor VIIa, trypsin, and in integrin receptor antagonists, used to treat many blood-coagulation disorders. Nitric oxide (NO), which is produced by oxidation of L-arginine in an NADPH- and O(2)-dependent process catalyzed by isoforms of nitric oxide synthase (NOS), exhibits diverse roles in both normal and pathological physiologies and has been postulated to be a contributor to the etiology of various diseases. Development of NOS inhibitors as well as analogs and mimetics of the natural substrate L-arginine, is desirable for potential therapeutic use and for a better understanding of their conformation when bound in the arginine binding site. The guanidino residue of arginine in many substrates, inhibitors, and antagonists forms strong ionic interactions with the carboxylate of an aspartic acid moiety, which provides specificity for the basic amino acid residue in the active side. However, a highly basic guanidino moiety incorporated in enzyme inhibitors or receptor antagonists is often associated with low selectivity and poor bioavailability after peroral application. Thus, significant effort is focused on the design and preparation of arginine mimetics that can confer selective inhibition for specific trypsin-like serine proteases and NOS inhibitors as well as integrin receptor antagonists and possess reduced basicity for enhanced oral bioavailability. This review will describe the survey of arginine mimetics designed to mimic the function of the arginine moiety in numerous peptidomimetic compounds (thrombin inhibitors, factor Xa inhibitors, factor VIIa inhibitors, integrin receptor antagonists, nitric oxide synthase inhibitors), with the aim of obtaining better activity, selectivity and oral bioavailability.
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PMID:Arginine mimetic structures in biologically active antagonists and inhibitors. 1716 27

Coagulation factor VIIa (FVIIa) belongs to a family of proteases being part of the stepwise, self-amplifying blood coagulation cascade. To investigate the impact of the mutation Met(298{156})Lys in FVIIa, we replaced the Gly(283{140})-Met(298{156}) loop with the corresponding loop of factor Xa. The resulting variant exhibited increased intrinsic activity, concurrent with maturation of the active site, a less accessible N-terminus, and, interestingly, an altered macromolecular substrate specificity reflected in an increased ability to cleave factor IX (FIX) and a decreased rate of FX activation compared to that of wild-type FVIIa. In complex with tissue factor, activation of FIX, but not of FX, returned to normal. Deconvolution of the loop graft in order to identify important side chain substitutions resulted in the mutant Val(158{21})Asp/Leu(287{144})Thr/Ala(294{152})Ser/Glu(296{154}) Ile/Met(298{156})Lys-FVIIa with almost the same activity and specificity profile. We conclude that a lysine residue in position 298{156} of FVIIa requires a hydrophilic environment to be fully accommodated. This position appears critical for substrate specificity among the proteases of the blood coagulation cascade due to its prominent position in the macromolecular exosite and possibly via its interaction with the corresponding position in the substrate (i.e. FIX or FX).
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PMID:A loop of coagulation factor VIIa influencing macromolecular substrate specificity. 1718 39

Activated coagulation factor V functions as a cofactor to factor Xa in the conversion of prothrombin to thrombin. Based on the introduction of extra carbohydrate side chains in recombinant factor V, we recently proposed several regions in factor Va to be important for factor Xa binding. To further define which residues are important for factor Xa binding, we prepared fifteen recombinant factor V variants in which clusters of charged amino acid residues were mutated, mainly to alanines. The factor V variants were expressed in COS-1 cells, and their functional properties evaluated in a prothrombinase-based assay, as well as in a direct binding test. Four of the factor V variants, 501A/510A/511D, 501A/510A/511D/513A, 513A/577A/578A, and 501A/510A/511D/513A/577A/578A exhibited markedly reduced factor Xa-cofactor activity tested in the prothrombinase assay, and reduced binding affinity as judged by the direct binding assay. These factor Va variants were normally cleaved at Arg-506 by activated protein C, and the interaction between the factor Xa-factor Va complex and prothrombin was unaffected by the introduced mutations. Based on the integration of all available data, we propose a key factor Xa binding surface to be centered on Arg-501, Arg-510, Ala-511, Asp-513, Asp-577, and Asp-578 in the factor Va A2 domain. These residues form an elongated charged factor Xa binding cluster on the factor Va surface.
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PMID:Mapping of the factor Xa binding site on factor Va by site-directed mutagenesis. 1850 57


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