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.
Agboh
Kelvin C
KC
Department of Cell Physiology and Pharmacology, University of Leicester, P. O. Box 138, Leicester LE1 9HN, United Kingdom.
Webb
Tania E
TE
Evans
Richard J
RJ
Ennion
Steven J
SJ
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