PDBsum entry 2hvk

Membrane protein

PDB id: 2hvk

Contents

Protein chains

219 a.a.

212 a.a.

103 a.a.

Ligands

F09

L2C

TBA

Metals

__K ×6

Waters ×178

References listed in PDB file

Key reference

Title

Crystallographic study of the tetrabutylammonium block to the kcsa k(+) channel.

Authors

S.Yohannan, Y.Hu, Y.Zhou.

Ref.

J Mol Biol, 2007, 366, 806-814. [DOI no: 10.1016/j.jmb.2006.11.081]

PubMed id

17196615

Abstract

K(+) channels play essential roles in regulating membrane excitability of many diverse cell types by selectively conducting K(+) ions through their pores. Many diverse molecules can plug the pore and modulate the K(+) current. Quaternary ammonium (QA) ions are a class of pore blockers that have been used for decades by biophysicists to probe the pore, leading to important insights into the structure-function relation of K(+) channels. However, many key aspects of the QA-blocking mechanisms remain unclear to date, and understanding these questions requires high resolution structural information. Here, we address the question of whether intracellular QA blockade causes conformational changes of the K(+) channel selectivity filter. We have solved the structures of the KcsA K(+) channel in complex with tetrabutylammonium (TBA) and tetrabutylantimony (TBSb) under various ionic conditions. Our results demonstrate that binding of TBA or TBSb causes no significant change in the KcsA structure at high concentrations of permeant ions. We did observe the expected conformational change of the filter at low concentration of K(+), but this change appears to be independent of TBA or TBSb blockade.

Figure 1.
Figure 1. Structure of KcsA. The gray lines represent the level of the cell membrane. KcsA (two subunits shown) is displayed in a ribbon representation. The TVGYG selectivity filter signature sequence and residues lining the cavity wall are shown as ball-and-stick. Ions (green spheres) and water molecules (red spheres) are covered with an electron density map (2F[o]–F[c], contoured at 2σ) to validate their positions. Figure 1. Structure of KcsA. The gray lines represent the level of the cell membrane. KcsA (two subunits shown) is displayed in a ribbon representation. The TVGYG selectivity filter signature sequence and residues lining the cavity wall are shown as ball-and-stick. Ions (green spheres) and water molecules (red spheres) are covered with an electron density map (2F[o]–F[c], contoured at 2σ) to validate their positions.

Figure 2.
Figure 2. Structures of the KcsA selectivity filter solved in a high concentration of K^+ (a), Rb^+ (b), Tl^+ (c), and a low concentration of K^+ (d). The structures solved in the absence of TBA are colored in yellow (PDB code 1K4C (a), 1R3I (b), 1R3J (c) and 1K4D (d)). The structures solved in the presence of TBA are colored in red, covered with F[o]–F[c] omit map (blue, contoured at 3σ ((a), (b) and (d)) or 2.5 σ (c)). The maps are calculated using a model with both the filter (residues T74 to G79) and ions removed. The pink electron density maps are F[o]^TBSb–F[o]^TBA difference maps countered at 10σ for (a) and (c), 18σ for (b), and 12 σ for (d). Figure 2. Structures of the KcsA selectivity filter solved in a high concentration of K^+ (a), Rb^+ (b), Tl^+ (c), and a low concentration of K^+ (d). The structures solved in the absence of TBA are colored in yellow (PDB code 1K4C (a), 1R3I (b), 1R3J (c) and 1K4D (d)). The structures solved in the presence of TBA are colored in red, covered with F[o]–F[c] omit map (blue, contoured at 3σ ((a), (b) and (d)) or 2.5 σ (c)). The maps are calculated using a model with both the filter (residues T74 to G79) and ions removed. The pink electron density maps are F[o]^TBSb–F[o]^TBA difference maps countered at 10σ for (a) and (c), 18σ for (b), and 12 σ for (d).

The above figures are reprinted by permission from Elsevier: J Mol Biol (2007, 366, 806-814) copyright 2007.