Figure 1. Transformation of spatial Ca²⁺ selectivity in Ca_V2.2 channels.

a, Ca_V2.2 CDI, low buffering. Left, cartoon of global Ca²⁺ elevation. Middle, exemplar traces in Ca²⁺ (red) and Ba²⁺ (black). Throughout, current bar references Ca²⁺ trace; Ba²⁺ trace normalized to Ca²⁺ peak. Right, average CDI; f₃₀₀ at 10 mV; data, mean ± SEM throughout; cell number in parentheses. b, Ca_V2.2 CDI, high buffering. Left, cartoon of local Ca²⁺ signaling. c, CDI of cBBBBb. d, Localizing spatial Ca²⁺ transforming element (yellow highlight) within NT_C. Top, exemplar currents for cBBBBb with amino-terminal deletions, (Δ82cBBBBb, removal of first 81 aa of cBBBBb; Δ81bBBBBb, removal of entire amino terminus of Ca_V2.2). Bottom, f₃₀₀ (high buffering) versus residues deleted from cBBBBb; left axis and circles with colors corresponding to exemplars above. K_d,EFF is also plotted on same abscissa; blue right axis and blue squares, with filled symbol corresponding to e. Extreme bottom, localized sequence for both CDI transformation and Ca²⁺/CaM binding within NT_C (yellow highlight).

e, f, FRET for YFP–CaM versus channel amino-terminal segments tagged with CFP. Left, construct schematics. Middle, FRET ratios (FR). Right, exemplar binding curves, with red symbols for Ca²⁺/CaM, and blue symbols for apoCaM (e, arrow shows K_d,EFF).