title: Ornatins: potent glycoprotein IIb-IIIa antagonists and platelet aggregation inhibitors from the leech Placobdella ornata.
abstract: The purification and characterization of six isoforms of ornatin, potent glycoprotein IIb-IIIa (GP IIb-IIIa) antagonists and platelet aggregation inhibitors are described. These isoforms were purified from whole leech homogenates of the leech Placobdella ornata, a North American leech commonly known as the turtle leech, by trichloroacetic acid precipitation, Sephadex G-50 size exclusion chromatography, GP IIb-IIIa affinity chromatography, and C18 reverse-phase HPLC. Each of the five completely sequenced isoforms, which range from 41 to 52 residues in length, contains the Arg-Gly-Asp (RGD) sequence, a common recognition sequence in adhesion proteins, as well as 6 cysteine residues; the positions of both of these features are conserved in the primary sequences. The amino acid sequences of ornatin isoforms B, C, D, and E are highly conserved, whereas ornatin A2 and A3 are less similar and lack 9 residues at the N-terminus. The ornatins are approximately 40% identical with decorsin, a GP IIb-IIIa antagonist isolated from the leech Macrobdella decora [Seymour, J. L., Henzel, W. J., Nevins, B., Stults, J. T. & Lazarus, R. A. (1990) J. Biol. Chem. 265, 10143-10147]; furthermore, the RGD sequence and 5 out of 6 cysteine residues are maintained in the same relative positions in both decorsin and ornatin. The ornatin isoforms do not exhibit significant similarity to any members of the snake-venom-derived family of GP IIb-IIIa antagonists [Dennis, M. S., Henzel, W. J., Pitti, R. M., Lipari, M. T., Napier, M. A., Deisher, T. A., Bunting, S. & Lazarus, R. A. (1990) Proc. Natl Acad. Sci. USA 87, 2471-2475] except in the RGD region of these proteins. The ornatin isoforms inhibit the binding of GP IIb-IIIa to immobilized fibrinogen with IC50 values ranging over 2.9-5.3 nM; ornatin isoforms A2, C, and E inhibit ADP-induced human platelet aggregation with IC50 values of about 130, 280, and 440 nM, respectively.
authors.affiliation: Department of Chemistry, Columbia University, New York.
authors.forename: P
authors.initials: P
authors.lastname: Mazur
authors.forename: W J
authors.initials: WJ
authors.lastname: Henzel
authors.forename: J L
authors.initials: JL
authors.lastname: Seymour
authors.forename: R A
authors.initials: RA
authors.lastname: Lazarus
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007447:Invertebrate Hormones / Q000302:isolation & purification* / Q000494:pharmacology; D007865:Leeches; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000302:isolation & purification*; D010980:Platelet Membrane Glycoproteins / Q000037:antagonists & inhibitors*; D012689:Sequence Homology, Nucleic Acid; D016339:Spectrometry, Mass, Fast Atom Bombardment
chemical_list: D007447:Invertebrate Hormones; D010975:Platelet Aggregation Inhibitors; D010980:Platelet Membrane Glycoproteins; C072214:ornatin