title: Bioinformatic analyses of male and female Amblyomma americanum tick expressed serine protease inhibitors (serpins).
abstract: Serine protease inhibitors (serpins) are a diverse family of proteins that is conserved across taxa. The diversity of Amblyomma americanum serpins (AAS) is far more complex than previously thought as revealed by discovery of 57 and 33 AAS transcripts that are respectively expressed in male and female A. americanum ticks, with 30 found in both. While distinct reproductively, both male and female metastriate ticks, such as A. americanum, require a blood meal. Thus, 30 AAS sequences found in both male and female ticks could play important role(s) in regulating tick feeding and thus represent attractive candidates for anti-tick vaccine development. Of significant interest, 19 AAS sequences expressed in male and female ticks are also part of the 48 AAS sequences expressed in fed female tick salivary glands or midguts; two organs through which the tick interacts with host blood and immune response factors. Considered the most important domain for serpin function, the reactive center loop (RCL) is further characterized by a single 'P1' site amino acid residue, which is central to determining the protease regulated by the serpin. In this study, a diversity of 17 different P1 site amino acid residues were predicted, suggesting that A. americanum serpins potentially regulate a large number of proteolytic pathways. Our data also indicate that some serpins in this study could regulate target protease common to all tick species, in that more than 40% of AAS show 58-97% inter-species amino acid conservation. Of significance, 24% of AAS showed 62-100% inter-species conservation within the functional RCL domain, with 10 RCLs showing ≥90-100% conservation. In vertebrates, serpins with basic residues at the P1 site regulate key host defense pathways, which the tick must evade to feed successfully. Interestingly, we found that AAS sequences with basic or polar uncharged residues at the putative P1 site are more likely to be conserved across tick species. Another notable observation from our data is that AAS sequences found only in female ticks and those found in both males and females, but not those found only in male ticks, were highly conserved in other tick species. While descriptive, this study provides the basis for more in-depth studies exploring the roles of serpins in tick feeding physiology.
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, United States.
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, United States.
authors.forename: Željko
authors.initials: Ž
authors.lastname: Radulović
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, United States.
authors.forename: Tae
authors.initials: T
authors.lastname: Kim
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade Federal do Rio de Janeiro - UFRJ, Rio de Janeiro, Brazil.
authors.forename: Gloria R C
authors.initials: GR
authors.lastname: Braz
authors.affiliation: Centro de Biotecnologia and Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9500, Prédio 43421, Porto Alegre 91501-970, RS, Brazil.
authors.forename: Itabajara
authors.initials: I
authors.lastname: Da Silva Vaz
authors.affiliation: Texas A & M University AgriLife Research, Department of Entomology, 2475 TAMU, College Station, TX 77843, United States. Electronic address: a-mulenga@tamu.edu.
authors.forename: Albert
authors.initials: A
authors.lastname: Mulenga
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019295:Computational Biology; D005260:Female; D041981:Gastrointestinal Tract / Q000378:metabolism; D026863:Ixodidae / Q000201:enzymology / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D010802:Phylogeny; D012469:Salivary Glands / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D015842:Serine Proteinase Inhibitors / Q000235:genetics*; D015843:Serpins / Q000235:genetics*
chemical_list: D015842:Serine Proteinase Inhibitors; D015843:Serpins
keywords: Amblyomma americanum; Orthologous serpins; Serine protease inhibitors (serpins); Tick feeding physiology