title: Molecular characterization of tick salivary gland glutaminyl cyclase.
abstract: Glutaminyl cyclase (QC) catalyzes the cyclization of N-terminal glutamine residues into pyroglutamate. This post-translational modification extends the half-life of peptides and, in some cases, is essential in binding to their cognate receptor. Due to its potential role in the post-translational modification of tick neuropeptides, we report the molecular, biochemical and physiological characterization of salivary gland QC during the prolonged blood feeding of the black-legged tick (Ixodes scapularis) and the gulf-coast tick (Amblyomma maculatum). QC sequences from I. scapularis and A. maculatum showed a high degree of amino acid identity to each other and other arthropods and residues critical for zinc binding/catalysis (D159, E202, and H330) or intermediate stabilization (E201, W207, D248, D305, F325, and W329) are conserved. Analysis of QC transcriptional gene expression kinetics depicts an upregulation during the bloodmeal of adult female ticks prior to fast-feeding phases in both I. scapularis and A. maculatum suggesting a functional link with bloodmeal uptake. QC enzymatic activity was detected in saliva and extracts of tick salivary glands and midguts. Recombinant QC was shown to be catalytically active. Furthermore, knockdown of QC transcript by RNA interference resulted in lower enzymatic activity, and small, unviable egg masses in both studied tick species as well as lower engorged tick weights for I. scapularis. These results suggest that the post-translational modification of neurotransmitters and other bioactive peptides by QC is critical to oviposition and potentially other physiological processes. Moreover, these data suggest that tick-specific QC-modified neurotransmitters/hormones or other relevant parts of this system could potentially be used as novel physiological targets for tick control.
authors.affiliation: Department of Biological Sciences, The University of Southern Mississippi, 118 College Drive # 5018, Hattiesburg, MS 39406, USA.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Adamson
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Browning
authors.forename: Chien-Chung
authors.initials: CC
authors.lastname: Chao
authors.forename: Robert C
authors.initials: RC
authors.lastname: Bateman
authors.forename: Wei-Mei
authors.initials: WM
authors.lastname: Ching
authors.forename: Shahid
authors.initials: S
authors.lastname: Karim
mesh_terms: D000595:Amino Acid Sequence; D019881:Aminoacyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D060829:Arthropod Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005260:Female; D018884:Ixodes / Q000737:chemistry / Q000201:enzymology / Q000235:genetics; D026863:Ixodidae / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D008297:Male; D008969:Molecular Sequence Data; D012469:Salivary Glands / Q000737:chemistry / Q000201:enzymology; D017386:Sequence Homology, Amino Acid
chemical_list: D060829:Arthropod Proteins; D019881:Aminoacyltransferases; C059280:glutaminyl-peptide cyclotransferase
keywords: AmQC; Amblyomma maculatum QC; Glutaminyl cyclase; IsQC; Ixodes scapularis QC; MG; Post-translational modification; QC; RNA interference; SG; Tick neuropeptides; glutaminyl cyclase; midgut; salivary gland