Figure 4.

The AC region in the RCK1 domain is important for Ca²⁺ sensitivity. (A) Ca²⁺ sensitivity of activation in chimeric channels of mSlo1 and dSlo1. The vertical axis shows schematic representation of chimera constructs with dSlo1 portions shaded gray and mSlo1 black. Rectangles are transmembrane segments or RCK1 domains (Jiang et al., 2002a), ovals are the Ca²⁺ bowl (Schreiber et al., 1999). Free energy increase in response to increase in [Ca²⁺]_i (shown at the right) for each chimera and WT channel was normalized against that for mSlo1. (B) Plot of V_1/2 versus [Ca²⁺]_i for mSlo1 (thin black line), dSlo1 (thick black line), and the chimeric channels as defined in A. V_1/2 values are obtained by fitting the G-V relations of the channels at various [Ca²⁺]_i with the Boltzmann equation.