Allosteric models include the five-state gating polarity model. (A and C) K A and KB are voltage-dependent transitions; CVR is the reference (i.e., CVR = 1). L, N, and M are voltage-independent transitions. α, β, δ, and γ are allosteric factors. Voltage-dependent steps, KA and KB, are bolded to indicate they are constrained such that the values for KA and KB used for fitting HHHEH are used for all HHHE-X chimeras. C and O are the closed and open state of the pore, respectively. V is the state of the voltage sensor where VR is at rest. Subscripts H and D describe the states upon membrane hyperpolarization and depolarization, respectively. Equations for calculating PO−V plots are described in Materials and methods. In B and D, PO−V scatter plot data are adapted from Lin et al. (2024), and fittings of the PO−V plots to the corresponding gating schemes are shown as a solid black line. Parameters for allosteric models are reported in Tables S4 and S5. (A) Gating scheme of the six-state allosteric model. (B)PO−V plots fitting the six-state allosteric model to PO−V scatter plot data of HHHEH (diamond ♦), HHHEK (pentagram ★), and HHHEA (left-pointing triangle ◄). (C) Gating scheme of the seven-state allosteric model. (D)PO−V plots fitting the seven-state allosteric model to PO−V scatter plot data of HHHEH (diamond ♦), HHHEK (pentagram ★), and HHHEA (left-pointing triangle ◄).