title: A blood meal-induced Ixodes scapularis tick saliva serpin inhibits trypsin and thrombin, and interferes with platelet aggregation and blood clotting.
abstract: Ixodes scapularis is a medically important tick species that transmits causative agents of important human tick-borne diseases including borreliosis, anaplasmosis and babesiosis. An understanding of how this tick feeds is needed prior to the development of novel methods to protect the human population against tick-borne disease infections. This study characterizes a blood meal-induced I. scapularis (Ixsc) tick saliva serine protease inhibitor (serpin (S)), in-house referred to as IxscS-1E1. The hypothesis that ticks use serpins to evade the host's defense response to tick feeding is based on the assumption that tick serpins inhibit functions of protease mediators of the host's anti-tick defense response. Thus, it is significant that consistent with hallmark characteristics of inhibitory serpins, Pichia pastoris-expressed recombinant IxscS-1E1 (rIxscS-1E1) can trap thrombin and trypsin in SDS- and heat-stable complexes, and reduce the activity of the two proteases in a dose-responsive manner. Additionally, rIxscS-1E1 also inhibited, but did not apparently form detectable complexes with, cathepsin G and factor Xa. Our data also show that rIxscS-1E1 may not inhibit chymotrypsin, kallikrein, chymase, plasmin, elastase and papain even at a much higher rIxscS-1E1 concentration. Native IxscS-1E1 potentially plays a role(s) in facilitating I. scapularis tick evasion of the host's hemostatic defense as revealed by the ability of rIxscS-1E1 to inhibit adenosine diphosphate- and thrombin-activated platelet aggregation, and delay activated partial prothrombin time and thrombin time plasma clotting in a dose-responsive manner. We conclude that native IxscS-1E1 is part of the tick saliva protein complex that mediates its anti-hemostatic, and potentially inflammatory, functions by inhibiting the actions of thrombin, trypsin and other yet unknown trypsin-like proteases at the tick-host interface.
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA; Federal University of São Carlos, Graduate Program in Genetics and Evolution, Brazil.
authors.forename: Adriana M G
authors.initials: AM
authors.lastname: Ibelli
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA.
authors.forename: Tae K
authors.initials: TK
authors.lastname: Kim
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA.
authors.forename: Creston C
authors.initials: CC
authors.lastname: Hill
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA.
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Lewis
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA.
authors.forename: Mariam
authors.initials: M
authors.lastname: Bakshi
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA; College Station High School, Science Department-Biology, 4002 Victoria Ave, College Station, TX 77845, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Miller
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA.
authors.forename: Lindsay
authors.initials: L
authors.lastname: Porter
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, USA. Electronic address: a-mulenga@tamu.edu.
authors.forename: Albert
authors.initials: A
authors.lastname: Mulenga
mesh_terms: D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects*; D003001:Cloning, Molecular; D015870:Gene Expression; D006801:Humans; D018884:Ixodes / Q000201:enzymology*; D008969:Molecular Sequence Data; D010843:Pichia / Q000235:genetics; D010974:Platelet Aggregation / Q000187:drug effects*; D012463:Saliva / Q000201:enzymology; D017422:Sequence Analysis, DNA; D015843:Serpins / Q000378:metabolism*; D013917:Thrombin / Q000037:antagonists & inhibitors*; D014357:Trypsin / Q000378:metabolism*
chemical_list: D015843:Serpins; D014357:Trypsin; D013917:Thrombin
keywords: Ixodes scapularis; Serine protease inhibitors; Tick anti-blood clotting function; Tick anti-platelet aggregation function; Tick-feeding physiology