Received for publication March 9, 2007.
Revised April 27, 2007.
Accepted for publication April 30, 2007.

APETx1 from sea anemone Anthopleura elegantissima is a gating modifier peptide toxin of the human ether-a-go-go-related (hERG) potassium channel

Abstract

We studied the mechanism of action and the binding site of APETx1, a peptide toxin purified from sea anemone, on the hERG channel. Similar to the effects of gating modifier toxins (hanatoxin and SGTx) on the Kv2.1 channel, APETx1 shifts the voltage-dependence of hERG activation in the positive direction and suppresses its current amplitudes elicited by strong depolarizing pulses that maximally activate the channels. The APETx1 binding site is distinctly different from that of a pore-blocking peptide toxin, BeKm-1. Mutations in the S3b region of hERG have dramatic impact on the responsiveness to APETx1: G514C potentiates while E518C abolishes APETx1 effect. Restoring the negative charge at position 518 (MTSES modification of 518C) partially restores APETx1 responsiveness, supporting an electrostatic interaction between E518 and APETx1. Among the 3 hERG isoforms, hERG1 and hERG3 are equally responsive to APETx1 while hERG2 is insensitive. The key feature appears to be an arginine residue uniquely present at the 514-equivalent position in hERG2, where the other two isoforms possess a glycine. Our data show that APETx1 is a gating modifier toxin of the hERG channel, and its binding site shares characteristics with those of gating modifier toxin binding sites on other Kv channels.

Key words: Ion channel regulation, Structure determinations