KCNE2 uses More Domains than KCNE1 to Modulate KCNQ1 Channel Function

Abstract

KCNE1 & KCNE2 are both single membrane-passing peptides with amino- & carboxyl ends in extra- & intra-cellular compartments. They also share high sequence homology in the transmembrane (TM) and juxtamembranous regions. Yet the two have distinctly different effects when associated with the KCNQ1 channel. Understanding the structural basis for differential KCNQ1 modulation by the 2 KCNE subunits is prerequisite to drug design targeting such interactions. We use the techniques of NMR, cysteine (Cys)-scanning mutagenesis and voltage clamping to explore this issue. We learn the following: (1) KCNE2 differs from KCNE1 in the extracellular juxtamembranous region (helix vs unstructured loop). Cys substitution in this region has distinct impact on the gating kinetics and/or pore conductance of the KCNQ1/KCNE2 channel complex, but has little or no effects on the KCNQ1/KCNE1 channel function. (2) KCNE2 & KCNE1 sequences diverge in the carboxyl end. Truncating this region of KCNE1 (93 −129) does not interfere with its ability to modulate KCNQ1, while truncating the corresponding region of KCNE2 (98-123) abolishes its function as a KCNQ1 modulator. Intracellular application of a peptide corresponding to KCNE2 aa 98-123 reduces currents through KCNQ1, increases currents through KCNQ1/KCNE2, but has no effects on currents through KCNQ1/KCNE1. (3) Cys substitution along the TM helices of KCNE1 and KCNE2 affects the gating kinetics and/or pore conductance of the KCNQ1/KCNE channel complexes. Structural alignment suggests a rotation of KCNE2 relative to KCNE1 in terms of helical faces interacting with the pore domain and voltage-sensing domain of the KCNQ1 channel. We propose that while both KCNE subunits utilize their TM helices to interact with KCNQ1, the more rigid helical structure of KCNE2 allows it to allosterically modulate the KCNQ1 gating and ion permeation properties by the extracellular juxtamembranous and cytoplasmic carboxyl domains.