Illustration of BQ⁺ in the cytoplasmic vestibule of the connexin pore. The crystal structure of Cx26 by Maeda et al., (2009) with BQ⁺ placed in the wide vestibule constituted by NT domain, as suggested by the chimeric data, is shown. For clarity, only two of the six connexin subunits are illustrated. The NT and the TM2 domains of one of the subunits are shown in cyan and yellow, respectively. The pore funnel is formed by the NT TM1 and E1 domains, with the narrowest part ∼14.7 Å formed by amino-terminal ends of NT. Pore diameter at the cytoplasmic vestibule, constituted by the NT extending into TM2, widens to ∼40 Å. BQ⁺ (white) is shown in this wide vestibule. The placement and orientation of BQ⁺ is arbitrary. The image was prepared using PyMOL (http://www.pymol.org).