“Pocket” enclosing electrostatic interactions involving R3 in an mH_V1 chimera in the closed state. Colors indicate local hydrophobicity: gray, hydrophobic; tan, intermediate; pink, hydrophilic. mH_V1 Trp203 corresponds to human Trp²⁰⁷, and “R3” represents the third arginine in the H_V1 signature sequence. The authors propose that cation–π interaction between the conserved Trp and R3 may latch the channel closed. See Cherny et al. (2015).