title: Tick-derived Kunitz-type inhibitors as antihemostatic factors.
abstract: Endogenous Kunitz-type inhibitors target a large number of serine proteinases, including coagulation factors VIIa and Xa, but not thrombin. By contrast, several two-domain Kunitz inhibitors of this major procoagulant proteinase have been isolated from both soft ticks (e.g., ornithodorin from Ornithodoros moubata) and hard ticks (e.g., boophilin from Rhipicephalus (Boophilus) microplus). Surprisingly, these anticoagulants do not follow the canonical mechanism of proteinase inhibition. Instead, their N-terminal residues bind across the thrombin active-site cleft, while C-terminal modules interact with the basic exosite I. The reactive-site loop of boophilin remains fully accessible in its complex with thrombin, and might interact with FXa according to the standard mechanism. A conceptually similar inhibition mechanism is employed by a related inhibitor of the TF-FVIIa complex isolated from Ixodes scapularis, ixolaris. Significant variations to the Kunitz fold are encountered in several of these factors, and are particularly evident in the single-domain FXa inhibitor, O. moubata TAP, and in soft tick-derived platelet antiaggregants (e.g., O. moubata disagregin). Altogether, these antihemostatic factors illustrate the divergence between hard and soft ticks. The unsurpassed versatility of tick-derived Kunitz inhibitors establishes them as valuable tools for biochemical investigations, but also as lead compounds for the development of novel antithrombotics.
authors.affiliation: Institut de Recerca, Hospital de la Santa Creu i Sant Pau, Sant Antoni Maria Claret 167, 08025 Barcelona, Spain.
authors.forename: María Angeles
authors.initials: MA
authors.lastname: Corral-Rodríguez
authors.forename: Sandra
authors.initials: S
authors.lastname: Macedo-Ribeiro
authors.forename: Pedro José
authors.initials: PJ
authors.lastname: Barbosa Pereira
authors.forename: Pablo
authors.initials: P
authors.lastname: Fuentes-Prior
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000925:Anticoagulants / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007299:Insect Bites and Stings / Q000097:blood*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011480:Protease Inhibitors / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D013987:Ticks / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000925:Anticoagulants; D011480:Protease Inhibitors