Figure 1. Tetrameric Shaker-like Kv channels have two major intersubunit interfaces. (A) Schematic cartoon depicting subunit domain arrangement in Shaker-like Kv channels. Two diagonally opposed subunits of the tetrameric channel are shown. The PDs (magenta) from each subunit surround a central ion-conducting pore, while the VSDs (blue) are physically isolated at the periphery. The conserved N-terminal cytoplasmic assembly domains (T1, black) form a ring beneath the pore. (B) A more detailed cartoon of the tetrameric ion conducting pore from an extracellular perspective, with adjacent subunits differentially shaded. Transmembrane helices S5 and S6 are depicted with cylinders, and a selectivity filter helix is shown as a black ribbon. The pore-lining S6 helix forms a major intersubunit interface (arrows), and the intracellular side comprises the activation gate. (C) Cartoon of the cytoplasmic T1 ring with adjacent subunits differentially shaded. There are major intersubunit contacts between neighboring, but not diagonally opposed, T1s (arrows). Helices are depicted with cylinders, and β-sheets are depicted with rectangles. (D) Amino acid alignment of mouse Kv2.1 and Kv6.4 with residue numbers given at the right margin. Identical residues are shaded black, and conservative substitutions are shaded gray. The T1 domain is underlined in magenta, transmembrane domains S1–S6 are underlined in dark blue, and the PD is underlined in light blue. The alignment was produced with the CLUSTALW algorithm as implemented in MEGA7 (Kumar et al., 2016), and un-conserved N and C termini have been trimmed. (E) T1 self-incompatibility in regulatory subunits (blue) theoretically allows formation of heterotetramers with a single (3:1R) or two diagonally opposed (2:2R) regulatory subunits because four compatible T1 contacts (+ signs) remain in each case. However, T1 self-incompatibility rules out formation of 2:2R with adjacent regulatory subunits, 1:3R and 4R tetramers, all of which have at least one incompatible intersubunit contact (minus signs).
Figure 1.

Tetrameric Shaker-like Kv channels have two major intersubunit interfaces. (A) Schematic cartoon depicting subunit domain arrangement in Shaker-like Kv channels. Two diagonally opposed subunits of the tetrameric channel are shown. The PDs (magenta) from each subunit surround a central ion-conducting pore, while the VSDs (blue) are physically isolated at the periphery. The conserved N-terminal cytoplasmic assembly domains (T1, black) form a ring beneath the pore. (B) A more detailed cartoon of the tetrameric ion conducting pore from an extracellular perspective, with adjacent subunits differentially shaded. Transmembrane helices S5 and S6 are depicted with cylinders, and a selectivity filter helix is shown as a black ribbon. The pore-lining S6 helix forms a major intersubunit interface (arrows), and the intracellular side comprises the activation gate. (C) Cartoon of the cytoplasmic T1 ring with adjacent subunits differentially shaded. There are major intersubunit contacts between neighboring, but not diagonally opposed, T1s (arrows). Helices are depicted with cylinders, and β-sheets are depicted with rectangles. (D) Amino acid alignment of mouse Kv2.1 and Kv6.4 with residue numbers given at the right margin. Identical residues are shaded black, and conservative substitutions are shaded gray. The T1 domain is underlined in magenta, transmembrane domains S1–S6 are underlined in dark blue, and the PD is underlined in light blue. The alignment was produced with the CLUSTALW algorithm as implemented in MEGA7 (Kumar et al., 2016), and un-conserved N and C termini have been trimmed. (E) T1 self-incompatibility in regulatory subunits (blue) theoretically allows formation of heterotetramers with a single (3:1R) or two diagonally opposed (2:2R) regulatory subunits because four compatible T1 contacts (+ signs) remain in each case. However, T1 self-incompatibility rules out formation of 2:2R with adjacent regulatory subunits, 1:3R and 4R tetramers, all of which have at least one incompatible intersubunit contact (minus signs).

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