Three-Dimensional Structure of a Voltage-Gated Potassium Channel at 2.5 nm Resolution

Abstract

The two-domain architecture of the Shaker channel is consistent with the recently proposed "hanging gondola" model for the T1 domain, putting the T1 domain at a distance from the membrane domain but attached to it by thin connectors. The space between the two domains is sufficient to permit cytoplasmic access of ions and the N-terminal inactivation domain to the pore region. A hanging gondola architecture has also been observed in the nicotinic acetylcholine receptor and the KcsA structure, suggesting that it is a common element of ion channels.

Fluorescence measurements reveal stoichiometry of K + channels formed by modulatory and delayed rectifier α-subunits

“…4), which predicts that a square with a side length of 66 Å measures exactly 93 Å across. These findings corroborate the notion that heteromeric channels are indeed tetramers with subunits arranged in a quadratic fashion around the central pore, and correlate well with Kv channel dimensions determined by singleparticle EM (26,28). For the above calculations, we used an R 0 value of 49.2 Å (29), which assumes a relative dipole orientation factor 2 of 2͞3.…”

“…First, FRET is limited to fluorophores Ͻ10 nm apart, and Kv channels can be approximated as squares that measure Ϸ10 nm across (25,26). Second, E did not vary significantly with different YFP or CFP intensities, and thus, was independent of the channel density (27).…”

Structural basis of two-stage voltage-dependent activation in K+channels

“…A variety of distance constraints based on experimental data were modeled as artificial distance-energy restraints in the form of a quadratic function with harmonic force constants of 5-20 kcal⅐[mol Å 2 ] Ϫ1 (7). Models were based on the following reasonable assumptions: (i) the central pore in voltagegated K ϩ channels is similar in structure to KcsA (1), which is consistent with the high degree of sequence similarity between Shaker and KcsA, with toxin-binding data, and with the generation of functional chimeric channels containing the Shaker voltage sensor and the KcsA pore (8,9); (ii) S1-S4 form transmembrane ␣-helices that are oriented roughly perpendicular to the plane of the membrane, which is consistent with alanine and tryptophan scanning mutagenesis of these segments in voltage-gated K ϩ channels (10-12); (iii) the voltage sensor and pore domains interact closely in the structure, which is supported by single-particle electron microscope images of Shaker channels at 25-Å resolution (13), by perturbation analysis of the pore domain (14), by distance measurements using lanthanide-based resonance energy transfer (15) and tethered quaternary ammonium pore blockers (16), and by electrostatic calculations (17).…”

The carboxyl-terminal region of cyclic nucleotide-modulated channels is a gating ring, not a permeation path

“…Because of the fourfold symmetry of the channel, there most likely would be four such windows, which leads to a picture reminiscent of the T1 domain of Shaker and Kv K ϩ channels. The T1 domain hangs below the channel pore, held by four proteinaceous columns separating permeation windows in a ''hanginggondola'' or ''fenestrated-rotunda'' conformation (52)(53)(54). In HCN and CNG channels, however, the gondola is formed by the carboxylterminal region, not the amino-terminal region as with the T1 domain.…”