Molecular and expression analysis of a family of the Amblyomma americanum tick Lospins
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Serine proteinase inhibitors (serpins) are a family of structurally similar but functionally diverse proteins that regulate several important proteolytic cascades in most branches of life. We have characterized 17 Amblyomma americanum serpin cDNAs here named as ;Lospins' (L; an acronym for Lone Star tick serpin) that possess three beta-sheets, eight alpha-helices and a reactive center loop consistent with the consensus serpin superfamily secondary structures. Visual inspection of deduced amino acid sequences revealed two patterns of basic residues: (i) (86)DKSRVLKAYKRL(97) in L5 and L13-16 and (ii) (158)VRDKTRGKI(166) in all Lospins, which are similar to consensus glycosaminoglycan (GAG) binding sites (XBnXmBX, where X and B are non-basic and basic residues, n=1 or 2 and m=1, 2 or 3). On three-dimensional models, the two putative GAG binding sites mapped onto alpha-helices D and F, respectively, with calculation of electrostatic surface potentials revealing basic patches on L5 and L13-16 models that are comparable to the heparin-binding site on antithrombin. RT-PCR expression analysis of 15 selected genes showed that the majority (11/15) of the Lospins were ubiquitously expressed in the midgut, ovary and salivary glands. On a neighbor-joining phylogeny guide tree, 15 serpins from other ticks and 17 Lospins from this study, a total of 32 tick serpin sequences, segregated into five groups with Lospins in groups A and D being conserved across tick species. The discovery of Lospins in this study sets the framework for future studies to understand the role of serpins in tick physiology.
author list (cited authors)
Mulenga, A., Khumthong, R., & Blandon, M. A.