title: Characterization of Ixophilin, a thrombin inhibitor from the gut of Ixodes scapularis.
abstract: Ixodes scapularis, the black-legged tick, vectors several human pathogens including Borrelia burgdorferi, the agent of Lyme disease in North America. Pathogen transmission to the vertebrate host occurs when infected ticks feed on the mammalian host to obtain a blood meal. Efforts to understand how the tick confronts host hemostatic mechanisms and imbibes a fluid blood meal have largely focused on the anticoagulation strategies of tick saliva. The blood meal that enters the tick gut remains in a fluid state for several days during the process of feeding, and the role of the tick gut in maintaining the blood-meal fluid is not understood. We now demonstrate that the tick gut produces a potent inhibitor of thrombin, a key enzyme in the mammalian coagulation cascade. Chromatographic fractionation of engorged tick gut proteins identified one predominant thrombin inhibitory activity associated with an approximately 18 kDa protein, henceforth referred to as Ixophilin. The ixophilin gene was preferentially transcribed in the guts of feeding nymphs. Expression began after 24 hours of feeding, coincident with the flow of host blood into the tick gut. Immunity against Ixophilin delayed tick feeding, and decreased feeding efficiency significantly. Surprisingly, immunity against Ixophilin resulted in increased Borrelia burgdorferi transmission to the host, possibly due to delayed feeding and increased transmission opportunity. These observations illuminate the potential drawbacks of targeting individual tick proteins in a functional suite. They also underscore the need to identify the "anticoagulome" of the tick gut, and to prioritize a critical subset of anticoagulants that could be targeted to efficiently thwart tick feeding, and block pathogen transmission to the vertebrate host.
authors.affiliation: Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Sukanya
authors.initials: S
authors.lastname: Narasimhan
authors.forename: Oriana
authors.initials: O
authors.lastname: Perez
authors.forename: Sara
authors.initials: S
authors.lastname: Mootien
authors.forename: Kathleen
authors.initials: K
authors.lastname: DePonte
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Koski
authors.forename: Erol
authors.initials: E
authors.lastname: Fikrig
authors.forename: Michel
authors.initials: M
authors.lastname: Ledizet
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D060829:Arthropod Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification / Q000494:pharmacology*; D005260:Female; D041981:Gastrointestinal Tract / Q000737:chemistry*; D015870:Gene Expression; D006801:Humans; D018884:Ixodes / Q000737:chemistry* / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification / Q000494:pharmacology; D016415:Sequence Alignment; D013917:Thrombin / Q000037:antagonists & inhibitors*
chemical_list: D060829:Arthropod Proteins; D011994:Recombinant Proteins; C586447:ixophilin protein, Ixodes scapularis; D013917:Thrombin