Figure 6. Ca²⁺/CaM competes with STIM2 K-rich domain's binding to PI(4,5)P₂.

(A) Binding of 2 μM reduced GFP, oxidized GFP-STIM2K dimer without Ca²⁺ and dimeric GFP–STIM2K pre-incubated with either 100 μM CaCl₂, 5 μM CaM, CaM1–2m, CaM3–4m or CaM1–4m in presence of 100 μM CaCl₂ to 2 mol% PI(4,5)P₂-containing PM-like liposomes in HK buffer. Binding of dimeric GFP–STIM2K pre-incubated with either 500 μM EGTA or 500 μM EGTA/5 μM CaM to 2 mol% PI(4,5)P₂ in HK buffer is also shown. Binding of 2 μM oxidized GFP-STIM2K dimer without Ca²⁺ to PM-like liposomes with 2 mol% PI(4,5)P₂ in HK buffer was set to 100. (B) Binding of 2 μM reduced GFP, oxidized GFP–STIM2K dimer without Ca²⁺ and dimeric GFP–STIM2K pre-incubated with either 100 μM CaCl₂, 5 μM CaM, CaM1-2m, CaM3-4m or CaM1–4m in presence of 100 μM CaCl₂ to 5 mol% PI(4,5)P₂-containing PC liposomes in HK buffer. Binding of 2 μM oxidized GFP–STIM2K dimer without Ca²⁺ to PC liposomes with 5 mol% PI(4,5)P₂ in HK buffer was set to 100 and bars indicate mean±S.D. from at least three experiments (*P<0.05, **P<0.005 and n.s. according to Student's t test).