Figure 1. Design template for engineering a temperature modulated ion channel.

(A) Arbitrary relative open probability vs voltage (P_OV) curves for a heat-sensing channel (top) and a cold-sensing channel (bottom) at two temperatures (red: high temperature, blue: low temperature). Arrows indicate the shifts in the curve on heating. (B) ΔG vs T profiles simulated using the equation: ΔG(T) = ΔH_C + ΔC_P(T−T_C) − TΔC_Pln(T/T_C) for two processes, one with a positive ΔC_P (solid curve, ΔC_P = 3 kcal/(mol.K)) and the other with a negative ΔC_P (dotted curve, ΔC_P = −3 kcal/(mol.K)) (see also Fig. S1). In both cases. the critical temperature, T_C, was 308K (35°C), at which the change in enthalpy, ΔH_C, was −3 kcal/mol. The heat sensing and cold sensing regimes of the curves are indicated by the red and blue colors respectively. (C) Relative P_OV curve of the wild-type Shaker K_V channel at 28°C (red) and 8°C (blue) (measured from tail currents) (see also Fig. S1). (D) A model of a hydrated voltage-sensor, deduced from the crystal structure of the K_V1.2/2.1 paddle chimera (see Extended experimental procedures in Supplementary Material), showing occupancy of water within the crevices of the voltage-sensor and the sites that were perturbed in this study. The S4 helix is shown as a cartoon while the S1-S3 helices are shown as ribbons. (E) Fractional buried surface area of different residues in the transmembrane segments S1-S3 (residues numbered according the 2R9R structure). The dotted horizontal lines indicate the cut-off for buried surface areas. The bars are colored according to the polarity index of the residue position, deduced from an alignment of 360 K_V channel sequences. Residues targeted in this study are marked with arrows, with the residue numbers corresponding to Shaker K_V channel. The residue marked with an asterisk, while enriched in polar residues in the alignment, is a hydrophobic residue in Shaker K_V channel and was not studied here.