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First published online August 31, 2007
Journal of Experimental Biology 210, 3188-3198 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.006494
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Molecular and expression analysis of a family of the Amblyomma americanum tick Lospins

Albert Mulenga*, Rabuesak Khumthong and Maria A. Blandon

Department of Entomology, College of Agriculture and Life Sciences, Texas A & M University, TAMU 2475, College Station, TX 77843, USA

* Author for correspondence (e-mail: a-mulenga{at}tamu.edu)

Accepted 28 June 2007

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 ß-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) 86DKSRVLKAYKRL97 in L5 and L13–16 and (ii) 158VRDKTRGKI166 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.

Key words: Amblyomma americanum, serine proteinase inhibitors (serpin), tick physiology glycosaminoglycan (GAG) binding site, tick vaccine






© The Company of Biologists Ltd 2007