RESUMO
Bioactive compounds of great interest are found in the saliva of hematophagous organisms. While exploring a cDNA library derived from the salivary glands of the tick Amblyomma cajennense, a transcript that codes for a protein with unique structure (containing an N-terminal Kunitz-type domain and a C-terminus with no homology to any annotated sequences) was found. The recombinant mature form of this protein ( approximately 13.5kDa) was produced in Escherichia coli BL21 (DE3), and it was able to inhibit Factor Xa (FXa) and extend global blood clotting times in vitro and ex vivo. Static and dynamic predictions of its tertiary structure indicate regions that may be related to its FXa inhibitor function.
Assuntos
Inibidores do Fator Xa , Fator Xa/química , Ixodidae/química , Inibidores de Serina Proteinase/química , Animais , Clonagem Molecular , DNA Complementar/genética , Fator Xa/metabolismo , Humanos , Ixodidae/genética , Ixodidae/metabolismo , Estrutura Terciária de Proteína/fisiologia , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Inibidores de Serina Proteinase/genética , Inibidores de Serina Proteinase/metabolismo , Relação Estrutura-AtividadeRESUMO
Bioactive compounds of great interest are found in the saliva of hematophagous organisms. While exploring a cDNA library derived from the salivary glands of the tick Amblyomma cajennense, a transcript that codes for a protein with unique structure (containing an N-terminal Kunitz-type domain and a C-terminus with no homology to any annotated sequences) was found. The recombinant mature form of this protein (¡13.5 kDa) was produced in Escherichia coli BL21 (DE3), and it was able to inhibit Factor Xa (FXa) and extend global blood clotting times in vitro and ex vivo. Static and dynamic predictions of its tertiary structure indicate regions that may be related to its FXa inhibitor function.
Assuntos
Animais , Anticoagulantes , Fator Xa , Saliva/fisiologia , SalivaRESUMO
BACKGROUND AND PURPOSE: Oncocalyxone A (OncoA) has a concentration-dependent anti-platelet activity. The present study aimed to further understand the mechanisms related to this effect. EXPERIMENTAL APPROACH: Human platelet aggregation was measured by means of a turbidimetric method. OncoA (32-256 microM) was tested against several platelet-aggregating agents, such as adenosine diphosphate (ADP), collagen, arachidonic acid (AA), ristocetin and thrombin. KEY RESULTS: OncoA completely inhibited platelet aggregation with a calculated mean inhibitory concentration (IC50-microM) of 122 for ADP, 161 for collagen, 159 for AA, 169 for ristocetin and 85 for thrombin. The anti-aggregatory activity of OncoA was not inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). OncoA, at a concentration that caused no significant anti-aggregatory activity, potentiated sodium nitroprusside (SNP) anti-aggregatory activity (18.8+/-2.9%-SNP vs 85.0+/-8.2%-SNP+OncoA). The levels of nitric oxide (NO) or cAMP were not altered by OncoA while cGMP levels were increased more than 10-fold by OncoA in resting or ADP-activated platelets. Flow cytometry revealed that OncoA does not interact with receptors for fibrinogen, collagen or P-selectin. Nevertheless, OncoA decreased the binding of antibodies to GP Ibalpha, a glycoprotein that is related both to von Willebrand factor and to thrombin-induced platelet aggregation. CONCLUSION AND IMPLICATIONS: OncoA showed anti-aggregatory activity in platelets that was associated with increased cGMP levels, not dependent on NO and with blocking GP Ibalpha glycoprotein. This new mechanism has the prospect of leading to new anti-thrombotic drugs.
Assuntos
Antraquinonas/farmacologia , AMP Cíclico/biossíntese , Inibidores da Agregação Plaquetária/farmacologia , Agregação Plaquetária/efeitos dos fármacos , Complexo Glicoproteico GPIb-IX de Plaquetas/metabolismo , Difosfato de Adenosina/farmacologia , Trifosfato de Adenosina/metabolismo , Adolescente , Adulto , Antraquinonas/isolamento & purificação , Antraquinonas/metabolismo , Plaquetas/efeitos dos fármacos , Plaquetas/metabolismo , AMP Cíclico/sangue , GMP Cíclico/sangue , Nucleotídeo Cíclico Fosfodiesterase do Tipo 5/sangue , Nucleotídeo Cíclico Fosfodiesterase do Tipo 5/metabolismo , Feminino , Citometria de Fluxo , Guanilato Ciclase/sangue , Guanilato Ciclase/metabolismo , Humanos , Técnicas In Vitro , Masculino , Pessoa de Meia-Idade , Óxido Nítrico/metabolismo , Inibidores da Agregação Plaquetária/metabolismo , Ligação Proteica , Tromboxano A2/fisiologiaRESUMO
Snake venom metalloproteinases (SVMPs) are multifunctional enzymes involved in several symptoms following snakebite, such as severe local hemorrhage. Multidomain P-III SVMPs are strongly hemorrhagic, whereas single domain P-I SVMPs are not. This indicates that disintegrin-like and cysteine-rich domains allocate motifs that enable catalytic degradation of ECM components leading to disruption of capillary vessels. Interestingly, some P-III SVMPs are completely devoid of hemorrhagic activity despite their highly conserved disintegrin-like and cysteine-rich domains. This observation was approached in the present study by comparing the effects of jararhagin, a hemorrhagic P-III SVMP, and berythractivase, a pro-coagulant and non-hemorrhagic P-III SVMP. Both toxins inhibited collagen-induced platelet aggregation, but only jararhagin was able to bind to collagen I with high affinity. The monoclonal antibody MAJar 3, that neutralizes the hemorrhagic effect of Bothrops venoms and jararhagin binding to collagen, did not react with berythractivase. The three-dimensional structures of jararhagin and berythractivase were compared to explain the differential binding to collagen and MAJar 3. Thereby, we pinpointed a motif within the Da disintegrin subdomain located opposite to the catalytic domain. Jararhagin binds to both collagen I and IV in a triple helix-dependent manner and inhibited in vitro fibrillogenesis. The jararhagin-collagen complex retained the catalytic activity of the toxin as observed by hydrolysis of fibrin. Thus, we suggest that binding of hemorrhagic SVMPs to collagens I and IV occurs through a motif located in the Da subdomain. This allows accumulation of toxin molecules at the site of injection, close to capillary vessels, where their catalytic activity leads to a local hemorrhage. Toxins devoid of this motif would be more available for vascular internalization leading to systemic pro-coagulant effects. This reveals a novel function of the disintegrin domain in hemorrhage formation.