CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
Modulation of hERG gating by a charge cluster in the
N-terminal 'proximal' domain
Johan B Saenen 1, Alain J Labro 1, Adam L Raes 1 and Dirk J Snyders 1*
1 University of Antwerpen
* To whom correspondence should be addressed. E-mail: dirk.snyders{at}ua.ac.be.
Submitted on April 19, 2006
Revised on May 16, 2006
Accepted on 30 August 2006
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Abstract |
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hERG potassium channels contribute to the repolarization
of the cardiac action potential and display unique gating
properties with slow activation and fast inactivation
kinetics. Deletions in the N-terminal 'proximal' domain
(residues 135-366) have been shown to induce
hyperpolarizing shifts in the voltage-dependence of
activation, suggesting that it modulates activation.
However, we did not observe a hyperpolarizing shift with a
subtotal deletion designed to preserve the local charge
distribution, and other deletions narrowed the region to
the KIKER containing sequence 362-372. Replacing the
positively charged residues of this sequence by negative
ones (EIEEE) resulted in a -45 mV shift of the
voltage-dependence of activation. The shifts were
intermediate for individual charge reversals, while E365R
resulted in a positive shift. Furthermore, the shifts in
the voltage-dependence were strongly correlated with the
net charge of the KIKER region. The apparent speeding of
the activation was attributable to the shifted
voltage-dependence of activation. Additionally, the
introduction of negative charges accelerated the
intermediate voltage-independent forward rate constant. We
propose that the modulatory effects of the 'proximal'
domain on hERG gating are largely electrostatic, localized
to the charged KIKER sequence.
Key Words:
Electrophysiology, Electrostatic interaction, Patch clamp, Potassium channel, Voltage gated, charge cluster
