title: Savignygrin, a platelet aggregation inhibitor from the soft tick Ornithodoros savignyi, presents the RGD integrin recognition motif on the Kunitz-BPTI fold.
abstract: Savignygrin, a platelet aggregation inhibitor that possesses the RGD integrin recognition motif, has been purified from the soft tick Ornithodoros savignyi. Two isoforms with similar biological activities differ because of R52G and N60G in their amino acid sequences, indicating a recent gene duplication event. Platelet aggregation induced by ADP (IC50, 130 nm), collagen, the thrombin receptor-activating peptide, and epinephrine was inhibited, although platelets were activated and underwent a shape change. The binding of alpha-CD41 (P2) to platelets, the binding of purified alpha(IIb)beta3 to fibrinogen, and the adhesion of platelets to fibrinogen was inhibited, indicating a targeting of the fibrinogen receptor. In contrast, the adhesion of osteosarcoma cells that express the integrin alpha(v)beta3 to vitronectin or fibrinogen was not inhibited, indicating the specificity of savignygrin toward alpha(IIb)beta3. Savignygrin shows sequence identity to disagregin, a platelet aggregation inhibitor from the tick Ornithodoros moubata that lacks an RGD motif. The cysteine arrangement of savignygrin is similar to that of the bovine pancreatic trypsin inhibitor family of serine protease inhibitors. A homology model based on the structure of the tick anticoagulant peptide indicates that the RGD motif is presented on the substrate-binding loop of the canonical BPTI inhibitors. However, savignygrin did not inhibit the serine proteases fXa, plasmin, thrombin, or trypsin. This is the first report of a platelet aggregation inhibitor that presents the RGD motif using the Kunitz-BPTI protein fold.
authors.affiliation: Department of Biochemistry, University of Pretoria, Pretoria 0002, South Africa.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Mans
authors.forename: Abraham I
authors.initials: AI
authors.lastname: Louw
authors.forename: Albert W H
authors.initials: AW
authors.lastname: Neitz
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D007611:Aprotinin / Q000737:chemistry; D001483:Base Sequence; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D020128:Inhibitory Concentration 50; D019476:Insect Proteins; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D026861:Ornithodoros / Q000378:metabolism; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000096:biosynthesis; D011485:Protein Binding; D017510:Protein Folding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000494:pharmacology*; D012469:Salivary Glands / Q000378:metabolism; D012471:Salivary Proteins and Peptides / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013329:Structure-Activity Relationship; D013987:Ticks; D013997:Time Factors
chemical_list: D018076:DNA, Complementary; D019476:Insect Proteins; D008024:Ligands; D009842:Oligopeptides; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D020033:Protein Isoforms; D011506:Proteins; D012471:Salivary Proteins and Peptides; C086086:disagregin; C460366:savignygrin protein, Ornithodoros savignyi; C047981:arginyl-glycyl-aspartic acid; D007611:Aprotinin