PDBsum entry 2aem

Metal transport, membrane protein

PDB id: 2aem

Contents

Protein chain

226 a.a. *

Waters ×5

* Residue conservation analysis

PDB id:

2aem

Name:

Metal transport, membrane protein

Title:

Crystal structures of the mthk rck domain

Structure:

Calcium-gated potassium channel mthk. Chain: a. Engineered: yes

Source:

Methanothermobacter thermautotrophicus. Organism_taxid: 145262. Gene: mthk. Expressed in: escherichia coli. Expression_system_taxid: 562.

Biol. unit:

Hexamer (from PDB file)

Resolution:

2.80Å R-factor: 0.224 R-free: 0.263

Authors:

J.Dong,N.Shi,I.Berke,L.Chen,Y.Jiang

Key ref:

J.Dong et al. (2005). Structures of the MthK RCK domain and the effect of Ca2+ on gating ring stability. J Biol Chem, 280, 41716-41724. PubMed id: 16227203 DOI: 10.1074/jbc.M508144200

Date:

22-Jul-05 Release date: 25-Oct-05

Protein chain

O27564  (MTHK_METTH) -  Calcium-gated potassium channel MthK from Methanothermobacter thermautotrophicus (strain ATCC 29096 / DSM 1053 / JCM 10044 / NBRC 100330 / Delta H)

Seq: 336 a.a.

Struc: 226 a.a.

DOI no: 10.1074/jbc.M508144200

J Biol Chem 280:41716-41724 (2005)

PubMed id: 16227203

Structures of the MthK RCK domain and the effect of Ca2+ on gating ring stability.

J.Dong, N.Shi, I.Berke, L.Chen, Y.Jiang.

ABSTRACT

MthK is a Ca2+-gated K+ channel from Methanobacterium autotrophicum. The crystal structure of the MthK channel in a Ca2+-bound open state was previously determined at 3.3 A and revealed an octameric gating ring composed of eight intracellular ligand-binding RCK (regulate the conductance of K+) domains. It was suggested that Ca2+ binding regulates the gating ring conformation, which in turn leads to the opening and closing of the channel. However, at 3.3 AA resolution, the molecular details of the structure are not well defined, and many of the conclusions drawn from that structure were hypothetical. Here we have presented high resolution structures of the MthK RCK domain with and without Ca2+ bound from three different crystals. These structures revealed a dimeric architecture of the RCK domain and allowed us to visualize the Ca2+ binding and protein-protein contacts at atomic detail. The dimerization of RCK domains is also conserved in other RCK-regulated K+ channels and transporters, suggesting that the RCK dimer serves as a basic unit in the gating ring assembly. A comparison of these dimer structures confirmed that the dimer interface is indeed flexible as suggested previously. However, the conformational change at the flexible interface is of an extent smaller than the previously hypothesized gating ring movement, and a reconstruction of these dimers into octamers by applying protein-protein contacts at the fixed interface did not generate enclosed gating rings. This indicated that there is a high probability that the previously defined fixed interface may not be fixed during channel gating. In addition to the structural studies, we have also carried out biochemical analyses and have shown that near physiological pH, isolated RCK domains form a stable octamer in solution, supporting the notion that the formation of octameric gating ring is a functionally relevant event in MthK gating. Additionally, our stability studies indicated that Ca2+ binding stabilizes the RCK domains in this octameric state.

Selected figure(s)

Figure 1.
FIGURE 1. Structures of RCK domains. A, a single subunit of the MthK RCK. B, a homodimer of the MthK RCK domain in a Ca^2+(gold sphere)-bound state. The two subunits are colored red and cyan. C, a homodimer of the E. coli RCK domain that has no C-terminal subdomain (Protein Data Bank code 1ID1). D, a homodimer of the KTN domain from M. jannaschii KtrA in a NAD-bound state (Protein Data Bank code 1LSS). Each subunit (ribbon style) and its bound NAD (ball-and-stick) are of the same color. The C-terminal region right after helix F was removed in the construct for crystallization.

Figure 3.
FIGURE 3. Superimposition of different MthK RCK structures. A, superimposition of two P2[1] crystal structures with (red) and without (black) Ca^2+. B, superimposition of the gating ring-forming RCK (black) with the RCK from the P2[1] crystal (red). C, superimposition of the gating ring-forming RCK (black) with RCK from the R32 crystal (red).

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2005, 280, 41716-41724) copyright 2005.

Figures were selected by the author.