Fig. 4: DeltaTag binding to PDEδ in the presence of Arl2.

a Kinetics of covalent modification of PDEδ (20 µM) by 6a (60 µM) in the presence of Arl2•GppNHp (20 µM). Data are presented as mean ± s.e.m., representative of biological replicates n = 3. b, c Competitive fluorescence polarisation assays in the presence of Arl2•GppNHp at r.t. (b) and 37 °C (c). The respective compound was incubated with PDEδ (40 nM), Arl2•GppNHp (40 nM) and FITC-labelled atorvastatin (FA-probe, 24 nM). Data are presented as mean ± s.e.m. (n = 4 for 6a at r.t., n = 3 for the rest). d, e In-lysate cellular thermal shift assay (CETSA) with incubation for 15 min (d) and 2 h (e). Data are presented as mean ± s.e.m., representative of biological replicates n = 3. f In-lysate covalent modification of PDEδ at 2 h, representative of biological replicates n = 3. g Time profile of in-lysate covalent modification of PDEδ by 6a, representative of biological replicates n = 3. h In-cell CETSA (15 min incubation). Data are presented as mean ± s.e.m., representative of biological replicates n = 3. i In-cell covalent modification of PDEδ at 2 h, representative of biological replicates n = 3. j Thermal proteome profiling (TPP). Volcano plot with −log₁₀ (p-value) against change in area under the melting curves (ΔAUC) is shown. Two-tailed p-values were determined by applying a paired t-test comparing the AUC of melting curves between DMSO-treated and compound-treated conditions, from biological replicates n = 3. Significance cut-offs: p-value ≤ 0.05, ΔAUC ≤ -1.5 or ≥1.5. Grey dots above threshold lines: false positive hits with no good fitting or inconsistent melting. Red dot: PDEδ (PDE6D) as the only significantly stabilised target. Blue dots: destabilised hits functionally linked to PDEδ. Representative fitted melting curves (PDEδ, Arl2 and Rheb) are shown, with DMSO controls in blue and compound-treated conditions in red. Orange frames: protein identification by at least two razor and unique peptides and a reporter ion intensity ≥ 1 × 10⁴ for the first three temperatures. Source data are provided as a Source Data file.