Figure 5. Ca²⁺ inhibits binding of STIM2 K-rich domain dimer to PI(4,5)P₂ liposomes.

(A) Binding of 1 μM GFP and oxidized GFP-STIM2K dimer to PM-like liposomes with 5 mol% PI(4,5)P₂ in HK buffer without Ca²⁺ and binding of GFP–STIM2K dimer in HK buffer with indicated Ca²⁺ concentrations. Binding of dimeric GFP–STIM2K in HK buffer without Ca²⁺ was set to 100. (B) Binding of 2 μM GFP and oxidized GFP–STIM2K dimer to PM-like liposomes with 5 mol% PI(4,5)P₂ in HK buffer without Ca²⁺ and binding of 2 μM oxidized GFP–STIM2K and GFP-STIM2K pre-incubated for 1 h with 100 μM CaCl₂/5 μM CaM to PM-like liposomes with 5 mol% PI(4,5)P₂ in HK buffer with 100 μM CaCl₂. Binding of GFP–STIM2K without CaCl₂ and CaM was set to 100. (C) Binding of 2 μM GFP–STIM2K dimer to PM-like liposomes with 2 mol% PI(4,5)P₂ in HK buffer without Ca²⁺ and binding of 2 μM dimeric GFP–STIM2K pre-incubated for 1 h with 5 μM CaM to PM-like liposomes with 2 mol% PI(4,5)P₂ in HK buffer with 50, 100 and 200 μM CaCl₂. Binding of GFP–STIM2K dimer in HK buffer without Ca²⁺ 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).