Affinity-guided labeling strategy for P2X7.

(A) Schematic representation of the P2X7 labeling strategy using ligand-directed N-cyanomethyl NASA chemistry. The biotin tag on the NASA molecule enables super-resolution imaging of nanoscale P2X7 localization using Strept-A 647 probe through a highly specific biotinylation reaction involving endogenous lysine (K) residues. Lg: P2X7 ligand. (B) Crystal structure of panda P2X7 (pdP2X7) shown in ribbon representation, bound to AZ10606120 depicted as spheres (PDB:5U1W) (42, 48). One of the three ATP-binding sites and the approximate location of the membrane are also indicated. Inset, enlarged view of the AZ10606120-binding pocket, rotated 180°. Distances (in Å) between the α-carbon of selected lysines and the hydroxyl group of AZ10606120 are displayed. Note that K300 is not visible in this view. (C) Chemical structure of X7-uP.

X7-uP is a potent P2X7 inhibitor that rapidly labels ectopically expressed P2X7 in HEK293T cells.

(A) Whole-cell currents evoked by 10 μM BzATP are reversibly inhibited by co-applying 1 μM X7-uP (upper trace) or 1 μM AZ10606120 (middle trace) in cells transiently transfected with rP2X7. Inhibitors were pre-applied alone for 8 s before 2 seconds of co-application. In the control (absence of inhibitors), BzATP-induced currents further increased, demonstrating current facilitation, which is an expected feature of P2X7 activation (47). (B) Summary of whole-cell inhibition (n = 4 cells for each condition). Bars represent mean ± s.e.m. (C) Western blot analysis of P2X7 labeling by X7-uP. Cells transiently transfected with P2X7c-myc were treated with 1 μM X7-uP for 0-60 minutes, in the absence or presence of 10 μM AZ10606120 or 10 μM A740003 (as indicated), followed by extensive washing. After cell lysis, biotinylated proteins were pulled down, separated on SDS-PAGE, and Western blotting was revealed using an anti-c-myc antibody (@c-myc). Molecular mass markers are shown on the right. Control of P2X7c-myc expression is presented in the corresponding input. β-Actin was used as a loading control. (D) Time course plot of P2X7 labeling with 1 μM X7-uP. Data (mean ± s.e.m., n = 3 independent transfections) were fitted with Eq. (1) to determine the pseudo-first-order reaction rate kapp (mean ± s.e.m.).

X7-uP labeling is highly selective for P2X7.

(A-B) Confocal images of HEK293T cells transiently transfected with either P2X7-mScarlet (A) or various P2X subunits tagged with GFP (P2X1-GFP, P2X2-GFP, P2X3-GFP, P2X4-GFP, P2X5-GFP, or P2X6-GFP) (B) were labeled with X7-uP and revealed using Strept-A 647 (red) in FBS-free DMEM. Labeling was performed in the presence of 10 μM AZ10606120 or 10 μM A740003 (A). Nuclei were stained with Hoechst (blue). For clarity, mScarlet and GFP signals are displayed in green. Scale bars, 10 μm. (C) Quantification of Alexa 647 fluorescence. Bars represent mean ± standard deviation (s.d.) (n = 75-129 cells, t-test comparisons to P2X7-mScarlet, ****P < 0.0001.

X7-uP labels K82 and K117 in rat P2X7.

(A) Molecular docking of 1 (same pose as shown in Figure 1 — figure supplement 1C) in pdP2X7, showing distances (in Å) between the reactive carbonyl of 1 (stick representation) and selected α-carbons of nearby residues (blue). Residues shown in parentheses correspond to equivalent rP2X7 residues. (B) Confocal images of HEK293T cells transiently transfected with different P2X7 constructs: P2X7-mScarlet, K82A, K117A, and K82A/K117A. Scale bars, 10 μm. (C) Quantification of Alexa 647 fluorescence. Bars represent mean ± s.d. (n = 90-190 cells, t-test comparisons to indicated conditions, ****P < 0.0001). (D) Whole-cell currents evoked by 10 μM BzATP are reversibly inhibited by co-application of 0.5 μM X7-uP (upper trace) to BzATP in a cell transiently transfected with the double mutant K82A/K117A. The control (absence of X7-uP) is shown in the bottom trace. (E) Summary of whole-cell inhibition for K82A/K117A (n = 7 cells for X7-uP and 5 cells for control). Bars represent mean ± s.e.m.; Mann-Whitney test (**P < 0.005).

dSTORM data revealed nanoscale P2X7 plasma membrane localization in BV2 cells.

(A) Cartoon and experimental timeline of BV2 cell treatments. IL-1β release was assessed in the supernatant (sup), and the same cells were labeled with 1 mM X7-uP after extensive washout. (B) Quantification of IL-1β release by ELISA following the indicated treatments: LPS (1 mg/mL for 24 h), ATP (1 mM for 30 min), BzATP (300 mM for 30 min), and MβCD (15 mM for 15 min). Bars represent mean ± s.e.m. (n = 12 samples from 3 independent experiments). Data were compared using Kruskal-Wallis followed by Dunn’s multiple comparisons (*P = 0.0208, #P = 0.0362, **P = 0.0014, ****P < 0.0001). (C) Normalized quantification of IL-1β release induced by LPS+ATP or LPS+BzATP in the presence of P2X7 inhibitors AZ10606120 or A740003. Bars represent mean ± s.e.m. (n = 6 samples from 6 independent experiments). One-way ANOVA with Dunnett’s multiple comparisons to control condition for ATP data (****P < 0.0001). Kruskal-Wallis followed by Dunn’s multiple comparisons to control condition for BzATP data (*P = 0.0414, *** P = 0.0006). (D) Bright-field and dSTORM images of X7-uP-labeled BV2 cells revealed with Strept-A 647 corresponding to experiments shown in panel b. Scale bars, 10 mm. Insets: Magnified dSTORM images. Scale bars, 1 mm. (E) Quantification of single P2X7 localization density. Bars represent mean ± s.e.m. (each data point represent a cell, n = 3 independent experiments). One-way ANOVA with Tukey’s multiple comparisons (*P < 0.019, #P < 0.0194, @P < 0.0477, ***P < 0.0002, ###P < 0.0008, ****P < 0.0001). (F) Relative frequency of cluster size. Inset: percentage of clusters larger than 0.025 mm2. (G) Number of detections per cluster. Bars represent mean ± s.e.m. One-way ANOVA with Tukey’s multiple comparisons (*P < 0.0197, #P < 0.0277, @P < 0.0389, ****P < 0.0001). (H) Images showing tessellation analysis of cells treated either with LPS+ATP or left untreated. Inset: magnification. Scale bars, 200 nm. (I) Number of fluorophores per cluster. Bars represent mean ± s.e.m. One-way ANOVA with Tukey’s multiple comparisons (****P < 0.0001).

Nanoscale redistribution of individual P2X7 receptors in microglia under pro-inflammatory conditions at the plasma membrane.

The cartoon illustrates two distinct clusters of P2X7 receptors (blue), each adorned with one, two, or three fluorescently tagged tetrameric biotin-bound streptavidin (red). In untreated cells, each cluster contains an average of 1.5 fluorophores per P2X7 receptor. Treatment with LPS and ATP promotes P2X7 clustering by increasing the average number of fluorophores per cluster to between 4 and 5, resulting in an increased number of P2X7 receptors per cluster, from one to three. This redistribution synergistically triggers IL-1β release.