title: Savignin, a potent thrombin inhibitor isolated from the salivary glands of the tick Ornithodoros savignyi (Acari: Argasidae).
abstract: A thrombin (E.C. 3.4.21.5) inhibitor, savignin, was isolated from the salivary glands of Ornithodoros savignyi by a combination of size exclusion, anion-exchange, and reversed-phase chromatography. The inhibitor has a molecular mass of 12,430.4 Da as determined by electrospray mass spectrometry. The behavior of savignin during anion-exchange chromatography indicated that it has an acidic pI. The available N-terminal sequence (residues 1-11) differed from that of ornithodorin with only one residue. Savignin inhibits thrombin-induced platelet aggregation, but has no effect on ADP- or collagen-induced aggregation. Kinetic studies indicated that savignin is a competitive, slow-, tight-binding inhibitor of alpha-thrombin (K(i) = 4.89 +/- 1.39 pM). Tight-binding kinetics showed that the inhibitor has a lower affinity for gamma-thrombin (K(i) = 22.3 +/- 5.9 nM). Plasmin, factor Xa, and trypsin are not inhibited by savignin.
authors.affiliation: Department of Biochemistry, University of Pretoria, Pretoria, 0002, South Africa.
authors.forename: J
authors.initials: J
authors.lastname: Nienaber
authors.forename: A R
authors.initials: AR
authors.lastname: Gaspar
authors.forename: A W
authors.initials: AW
authors.lastname: Neitz
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D006801:Humans; D019476:Insect Proteins; D007700:Kinetics; D013058:Mass Spectrometry; D008970:Molecular Weight; D010974:Platelet Aggregation / Q000187:drug effects; D012469:Salivary Glands / Q000737:chemistry; D015842:Serine Proteinase Inhibitors / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D013379:Substrate Specificity; D013917:Thrombin / Q000037:antagonists & inhibitors*; D013987:Ticks / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D019476:Insect Proteins; D015842:Serine Proteinase Inhibitors; C121778:savignin protein, Ornithodoros savignyi; D013917:Thrombin