Figure 6: ATP-binding-evoked alterations in interdomain hydrophobic interactions is crucial for P2X4 receptor activation.

(a) Illustrations of bound-ATP-evoked alterations in interdomain hydrophobic interactions between LF and DF domains. Dotted arrows indicate the movements of key residues and ATP after ATP-binding. (b) Representative current traces showing maximal amplitude of currents caused by saturated ATP (1–1.5 mM for ^rK190F, ^rI205W, ^rL214W, ^rI229F and ^rV288F; 100 μM for WT, ^rL188F and ^rL206A). (c) Pooled data for maximal current activated by saturated ATP for mutations of the residues involved in interdomain interactions (means±s.e.m., n=5–31). *P<0.05; **P<0.01 versus WT (dashed line), Student’s t-test. (d) Representative western blotting illustrating effects of various mutants on the cell surface expression of rP2X4. Similar results were obtained in three other independent experiments. (e) Effect of mutations on ATP-sensitivity of rP2X4. The solid line is a fit of the Hill equation to the pH-dependent activation. Each point represents the mean±s.e.m. of 3–6 measurements.