Mapping a novel positive allosteric modulator binding site in the central vestibule region of human P2X7

P2X7 receptors are important in the regulation of inflammatory responses and immune responses to intracellular pathogens such as Mycobacterium tuberculosis and Toxoplasma gondii. Enhancement of P2X7 receptor responses may be useful in pathogen clearance particularly in individuals with defective microbial killing mechanisms. Ginsenosides from Panax ginseng have been discovered to act as positive allosteric modulators of P2X7. Here we describe a novel modulator binding site identified by computational docking located in the central vestibule of P2X7 involving S60, D318, and L320 in the lower body β-sheets lining the lateral portals. Potentiation of ATP-mediated responses by ginsenosides CK and Rd caused enhanced ionic currents, Ca(2+) influx and YOPRO-1 uptake in stably transfected HEK-293 cells (HEK-hP2X7) plus enhanced cell death responses. Potentiation of ATP responses by CK and Rd was markedly reduced by mutations S59A, S60A, D318L and L320A supporting the proposed allosteric modulator binding site. Furthermore, mutation of the conserved residues S60 and D318 led to alterations in P2X7 response and a higher sensitivity to ATP in the absence of modulators suggesting residues in the connecting rods play an important role in regulating P2X7 gating. Identification of this novel binding site location in the central vestibule may also be relevant for structurally similar channels.