Tick saliva is a rich source of antihemostatic, anti-inflammatory, and immunomodulatory molecules that actively help the tick to finish its blood meal. Moreover, these molecules facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-8, a salivary serpin from the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Iripin-8 displayed blood-meal-induced mRNA expression that peaked in nymphs and the salivary glands of adult females. Iripin-8 inhibited multiple proteases involved in blood coagulation and blocked the intrinsic and common pathways of the coagulation cascade in vitro. Moreover, Iripin-8 inhibited erythrocyte lysis by complement, and Iripin-8 knockdown by RNA interference in tick nymphs delayed the feeding time. Finally, we resolved the crystal structure of Iripin-8 at 1.89 Å resolution to reveal an unusually long and rigid reactive center loop that is conserved in several tick species. The P1 Arg residue is held in place distant from the serpin body by a conserved poly-Pro element on the P' side. Several PEG molecules bind to Iripin-8, including one in a deep cavity, perhaps indicating the presence of a small-molecule binding site. This is the first crystal structure of a tick serpin in the native state, and Iripin-8 is a tick serpin with a conserved reactive center loop that possesses antihemostatic activity that may mediate interference with host innate immunity.

• Klíčová slova
• Ixodes ricinus, blood coagulation, crystal structure, parasite, saliva, serpin, tick,
• MeSH
• aktivace komplementu účinky léků   imunologie   fyziologie   MeSH
• erytrocyty metabolismus   MeSH
• exprese genu genetika   MeSH
• hemokoagulace účinky léků   fyziologie   MeSH
• klíště enzymologie   genetika   metabolismus   MeSH
• komplement metabolismus   MeSH
• lymeská nemoc MeSH
• nymfa MeSH
• proteiny členovců metabolismus   MeSH
• regulace genové exprese genetika   MeSH
• serpiny metabolismus   ultrastruktura   MeSH
• slinné žlázy metabolismus   MeSH
• sliny chemie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• komplement MeSH
• proteiny členovců MeSH
• serpiny MeSH

Tick saliva is a rich source of pharmacologically and immunologically active molecules. These salivary components are indispensable for successful blood feeding on vertebrate hosts and are believed to facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-3, a protein expressed in the salivary glands of the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Belonging to the serpin superfamily of protease inhibitors, Iripin-3 strongly inhibited the proteolytic activity of serine proteases kallikrein and matriptase. In an in vitro setup, Iripin-3 was capable of modulating the adaptive immune response as evidenced by reduced survival of mouse splenocytes, impaired proliferation of CD4+ T lymphocytes, suppression of the T helper type 1 immune response, and induction of regulatory T cell differentiation. Apart from altering acquired immunity, Iripin-3 also inhibited the extrinsic blood coagulation pathway and reduced the production of pro-inflammatory cytokine interleukin-6 by lipopolysaccharide-stimulated bone marrow-derived macrophages. In addition to its functional characterization, we present the crystal structure of cleaved Iripin-3 at 1.95 Å resolution. Iripin-3 proved to be a pluripotent salivary serpin with immunomodulatory and anti-hemostatic properties that could facilitate tick feeding via the suppression of host anti-tick defenses. Physiological relevance of Iripin-3 activities observed in vitro needs to be supported by appropriate in vivo experiments.

• Klíčová slova
• Ixodes ricinus, X-ray crystallography, adaptive immunity, blood coagulation, inflammation, saliva, serpin, tick,
• MeSH
• adaptivní imunita účinky léků   MeSH
• aktivace lymfocytů účinky léků   MeSH
• antikoagulancia izolace a purifikace   farmakologie   MeSH
• cytokiny metabolismus   MeSH
• hemokoagulace účinky léků   MeSH
• hmyzí proteiny izolace a purifikace   farmakologie   MeSH
• imunologické faktory izolace a purifikace   farmakologie   MeSH
• inhibitory proteas izolace a purifikace   farmakologie   MeSH
• klíště metabolismus   MeSH
• králíci MeSH
• kultivované buňky MeSH
• lidé MeSH
• lymfocyty účinky léků   imunologie   metabolismus   MeSH
• morčata MeSH
• myši inbrední C3H MeSH
• myši inbrední C57BL MeSH
• myši transgenní MeSH
• myši MeSH
• proliferace buněk účinky léků   MeSH
• slezina účinky léků   imunologie   metabolismus   MeSH
• slinné proteiny a peptidy izolace a purifikace   farmakologie   MeSH
• sliny metabolismus   MeSH
• zvířata MeSH
• Check Tag
• králíci MeSH
• lidé MeSH
• morčata MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• antikoagulancia MeSH
• cytokiny MeSH
• hmyzí proteiny MeSH
• imunologické faktory MeSH
• inhibitory proteas MeSH
• slinné proteiny a peptidy MeSH