Abstract 1097: N-Terminal Charges Modulate Gating Properties of hERG
Purpose: hERG K-channels contribute to the repolarization of the cardiac action potential and display unique gating properties with slow activation kinetics and a fast inactivation process. Previous work has shown that deletions in the N-terminal ’proximal domain’ (residues 135–366) shifted the voltage-dependence of activation towards more hyperpolarized potentials suggesting that it modulates the activation process.
Results: We did not observe a hyperpolarizing shift with a subtotal deletion (~200 residues) specifically designed to preserve the local charge distribution (midpoint 0.3 ± 1.5 mV vs 1.8 ± 1.8 mV in WT) (Fig. 1⇓). However, replacing the charges of the KIKER sequence starting at position 362 by negative ones (EIEEE) did result in a similar large hyperpolarizing shift of the voltage-depedence of activation (~-43mV). Furthermore, a strong correlation was observed between the net charge of the KIKER sequence and the shifted voltage-dependence expressed as free energy (Fig. 2⇓). In addition, the deactivation time constants were accelerated while the apparent speeding of the activation rates could be attributed to the shifted voltage-dependence of activation. Moreover, charge reversal in a second N-terminal cluster of basic residues also accelerated the deactivation, while the voltage-dependence of activation remained unaltered, consistent with reported effects caused by mutations or deletion of the PAS domain.
Conclusion: Overall, our results indicate that the N-terminus modulates the gating process of hERG, and we propose that this originates in large part from the local electric field of several charged sections located proximal to the S1 segment.