Figure 2. Domain-specific Interactions of CaM with Na_v1.2_IQp.

Emission spectra of Fl-Na_v1.2_IQp in the absence (solid line) and presence (dashed line) of slight excess of (A) apo CaM_1-80 (left), apo CaM_76-148 (middle), and apo CaM_1-148 (right) or (B) Ca²⁺-saturated CaM. C: Titration of Fl-Na_v1.2_IQp with apo CaM (open circles) or Ca²⁺-saturated CaM (filled diamonds). The titrations of apo CaM_1-80 were normalized to the maximum signal observed after addition of 10 mM CaCl₂ (Newman, 2008). For CaM_76-148 (middle), and CaM_1-148 (right), binding was stoichiometric and is plotted as a function of the ratio of [CaM_total]:[peptide], with an inset showing saturation versus [CaM_total]. D: Equilibrium Ca²⁺ titrations of CaM_1-80 (left), CaM_76-148 (middle), and CaM_1-148 (right) using intrinsic fluorescence to monitor Ca²⁺ binding in the absence of peptide [sites I and II (blue) or sites III and IV (red)], or after addition of excess Na_v1.2_IQp [sites I and II (cyan) and sites III and IV (orange)]. Supported by Tables S1 and S2.