|
|
|
|
|
|
|
||
ARTICLE |
Correspondence to Gail A. Robertson: robertson{at}physiology.wisc.edu
Human ether-à-go-go–related gene (hERG) channels mediate cardiac repolarization and bind drugs that can cause acquired long QT syndrome and life-threatening arrhythmias. Drugs bind in the vestibule formed by the S6 transmembrane domain, which also contains the activation gate that traps drugs in the vestibule and contributes to their efficacy of block. Although drug-binding residues have been identified, we know little about the roles of specific S6 residues in gating. We introduced cysteine mutations into the hERG channel S6 domain and measured mutational effects on the steady-state distribution and kinetics of transitions between the closed and open states. Energy-minimized molecular models based on the crystal structures of rKv1.2 (open state) and MlotiK1 and KcsA (closed state) provided structural contexts for evaluating mutant residues. The majority of mutations slowed deactivation, shifted conductance voltage curves to more negative potentials, or conferred a constitutive conductance over voltages that normally cause the channel to close. At the most intracellular extreme of the S6 region, Q664, Y667, and S668 were especially sensitive and together formed a ringed domain that occludes the pore in the closed state model. In contrast, mutation of S660, more than a full helical turn away and corresponding by alignment to a critical Shaker gate residue (V478), had little effect on gating. Multiple substitutions of chemically distinct amino acids at the adjacent V659 suggested that, upon closing, the native V659 side chain moves into a hydrophobic pocket but likely does not form the occluding gate itself. Overall, the study indicated that S6 mutagenesis disrupts the energetics primarily of channel closing and identified several residues critical for this process in the native channel.
Abbreviations used in this paper: CnErg-1, Centruroides noxius Erg-specific toxin; hERG, human ether-à-go-go–related gene; KcsA, Streptomyces lividans potassium channel; PDB, Protein Data Bank.
© 2008 Wynia-Smith et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.jgp.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Facebook 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
|
|
 |
|
  A. Oberai, N. H. Joh, F. K. Pettit, and J. U. Bowie Structural imperatives impose diverse evolutionary constraints on helical membrane proteins PNAS, October 20, 2009; 106(42): 17747 - 17750. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. S. Gustina and M. C. Trudeau A recombinant N-terminal domain fully restores deactivation gating in N-truncated and long QT syndrome mutant hERG potassium channels PNAS, August 4, 2009; 106(31): 13082 - 13087. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Z. Stepanovic, F. Potet, C. I. Petersen, J. A. Smith, J. Meiler, J. R. Balser, and S. Kupershmidt The evolutionarily conserved residue A653 plays a key role in HERG channel closing J. Physiol., June 1, 2009; 587(11): 2555 - 2566. [Abstract] [Full Text] [PDF]
|
|
|
|
