title: A novel phospholipase A2 activity in saliva of the lone star tick, Amblyomma americanum (L.).
abstract: Saliva from female lone star ticks, Amblyomma americanum, contained a novel phospholipase A2 (PLA2) activity that hydrolyzed 14C-arachidonate from 14C-arachidonyl phosphatidylcholine. The tick saliva PLA2 (ts-PLA2) was active over a broad pH range (4.5-11.5) with two distinct pH optima of pH 5.5 and 9.5. Though extracellular PLA2s are reported to be activated by millimolar Ca2+, ts-PLA2 was sensitive to submicromolar Ca2+ and was half-maximally activated by 3.5 microM Ca2+. Tick saliva contains > 500 microM Ca2+ and the feeding lesion in the host is expected to contain millimolar Ca2+. Saliva exhibited a single peak of PLA2 activity corresponding to a molecular weight of 55.7 +/- 1.3 kDa by size exclusion chromatography. The ts-PLA2 was unaffected by a variety of compounds known to inhibit either secreted or cytosolic PLA2s from other sources. However, ts-PLA2 was inhibited by the substrate analog, oleyloxyethyl phosphorylcholine (IC50 = 1.4 microM), and the end product, arachidonic acid (IC50 = 38 microM). Low concentrations of dithiothreitol did not greatly affect ts-PLA2, but activity was reduced at higher concentrations. The PLA2 activity found in A. americanum salivary glands showed many similarities to ts-PLA2, but also some distinct differences. Secreted at the tick-host interface, ts-PLA2 is thought to play an important, but unknown, role during the prolonged tick feeding.
authors.affiliation: Department of Entomology, Oklahoma State University, Stillwater 74048-0464, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Bowman
authors.forename: C L
authors.initials: CL
authors.lastname: Gengler
authors.forename: M R
authors.initials: MR
authors.lastname: Surdick
authors.forename: K
authors.initials: K
authors.lastname: Zhu
authors.forename: R C
authors.initials: RC
authors.lastname: Essenberg
authors.forename: J R
authors.initials: JR
authors.lastname: Sauer
authors.forename: J W
authors.initials: JW
authors.lastname: Dillwith
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002850:Chromatography, Gel; D005260:Female; D006863:Hydrogen-Ion Concentration; D010713:Phosphatidylcholines / Q000378:metabolism; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D010742:Phospholipid Ethers / Q000378:metabolism; D012463:Saliva / Q000201:enzymology; D012469:Salivary Glands / Q000201:enzymology; D013379:Substrate Specificity; D013696:Temperature; D013987:Ticks / Q000201:enzymology*; D013997:Time Factors
chemical_list: D010713:Phosphatidylcholines; D010742:Phospholipid Ethers; D016718:Arachidonic Acid; C043051:1-O-hexadecyl-2-arachidonyl-sn-glycero-3-phosphocholine; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium