Figure 1

Ca²⁺ dynamically controls rearrangement of MICU1 multimers in intact cells.

(A) Schematic illustration of the putative Ca²⁺-induced rearrangement of MICU1-CFP and MICU1-YFP hexamers that bind to the MCU/EMRE mitochondrial Ca²⁺ uptake machinery. It is hypothesized that Ca²⁺ binding to the MICU1 EF-hands reduces FRET between the respective MICU1-conjugated FPs. (B) Representative curve showing the MICU1 FRET ratio signal of HeLa cells co-expressing MICU1-CFP and MICU1-YFP upon cell treatment with 100 μM histamine in the presence of 2 mM Ca²⁺. (C) Representative images to panel b under basal condition, upon stimulation with 100 μM histamine 3 min. after stimulation (scale bar, 10 μm). (D) Representative MICU1 FRET ratio signals over time in HeLa cells upon addition and removal of different free Ca²⁺ concentrations in the presence of 3 μM ionomycin. The maximal ∆ MICU1 FRET ratio signal (between 3 mM EGTA and 1000 μM Ca²⁺) was defined as 100%. (E) Concentration response curve of the Ca²⁺-induced reduction of the MICU1 FRET ratio signal in HeLa cells that were treated with 3 μM ionomycin and different Ca²⁺ concentrations as shown in panel (D); mean ± SEM. (n = 7–9).