Functional characterization of a P2X receptor from Schistosoma mansoni.
The cloning and characterization of a P2X receptor (schP2X) from the parasitic blood fluke Schistosoma mansoni provides the first example of a non-vertebrate ATP-gated ion channel. A number of functionally important amino acid residues conserved throughout vertebrate P2X receptors, including 10 extracellular cysteines, aromatic and positively charged residues involved in ATP recognition, and a consensus protein kinase C site in the amino-terminal tail, are also present in schP2X. Overall, the amino acid sequence identity of schP2X with human P2X(1-7) receptors ranges from 25.8 to 36.6%. ATP evoked concentration-dependent currents at schP2X channels expressed in Xenopus oocytes with an EC(50) of 22.1 microM. 2',3'-O-(4-Benzoylbenzoyl)adenosine 5'-triphosphate (Bz-ATP) was a partial agonist (maximum response 75.4 +/- 4.4% that of ATP) with a higher potency (EC(50) of 3.6 microM) than ATP. Suramin and pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid blocked schP2X responses to 100 microm ATP with IC(50) values of 9.6 and 0.5 microM, respectively. Ivermectin (10 microM) potentiated currents to both ATP and Bz-ATP by approximately 60% with a minimal effect on potency (EC(50) of 18.2 and 1.6 microM, respectively). The relative permeability of schP2X expressed in HEK293 cells to various cations was determined under bi-ionic conditions. schP2X has a relatively high calcium permeability (P(Ca)/P(Na) = 3.80 +/- 0.29) and an estimated minimum pore diameter similar to that of vertebrate P2X receptors. SchP2X provides a useful comparative model for the better understanding of human P2X receptor function and may also provide an alternative drug target for treatment of schistosomiasis.
Department of Cell Physiology and Pharmacology, University of Leicester, P. O. Box 138, Leicester LE1 9HN, United Kingdom.
Kelvin C
KC
Agboh
Tania E
TE
Webb
Richard J
RJ
Evans
Steven J
SJ
Ennion
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002412:Cations / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004594:Electrophysiology; D015801:Helminth Proteins; D008969:Molecular Sequence Data; D010539:Permeability; D011493:Protein Kinase C; D018048:Receptors, Purinergic P2 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D058469:Receptors, Purinergic P2X; D012550:Schistosoma mansoni / Q000737:chemistry*; D017385:Sequence Homology
D002412:Cations; D015801:Helminth Proteins; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D000255:Adenosine Triphosphate; D011493:Protein Kinase C