Figure 1.

The presence of a tetramerization domain favors calmodulin binding to a membrane protein. (A and C) Tac-Kv7.2-CFP chimeras extracted from HEK293T cells were immunoprecipitated using anti-GFP antibodies, separated by SDS-PAGE, transferred to membranes (WB), and probed with anti-GFP and anti-CaM antibodies (n ≥ 3, see supplemental Figs 2 and 3 for the full blots). The bottom panel in (C) was obtained after a longer exposure than the top panel (see supplemental Fig. 3). (B) D-CaM (12.5 nM) fluorescence enhancement in the absence of Ca²⁺ (10 mM EGTA) at the indicated recombinant GST-fusion protein concentrations. The lines are the result of fitting a Hill equation to the data. The EC₅₀ (nM) was 17.8 ± 1.1 and 21.5 ± 0.5, for ABΔ2-CD and ABΔ2-Tet, respectively. The asterisks indicate significantly different maximal fluorescence: **p < 0.01. The data represent the means ± SEM from 3 independent experiments.