Figure 3.

Side view of the open human H_V1 channel, with the external end up. Transmembrane helices are colour-coded: S1 = red, S2 = yellow, S4 = blue and S3 is shown as lines to be unobtrusive. Key amino acids are labelled and shown with side chains as sticks. Asp¹¹² is crucial for selectivity; Phe¹⁵⁰ demarcates inner and outer aqueous vestibules and the three Arg in S4 sense voltage. Figure is based on the model of Li et al. [91]. Note that Asp¹¹² interacts with Asp²⁰⁸ [94], and Arg²¹¹ is below Phe¹⁵⁰, and thus is exposed to the inner vestibule. Drawn with PyMol.