Kermani, A. A. | bioRxiv Science

bioRxiv2025

Mechanisms of KCNQ1 gating modulation by KCNE1/3 for cell-specific function

KCNQ1 potassium channels are essential for physiological processes such as cardiac rhythm and intestinal chloride secretion. KCNE-family subunits (KCNE1-5) associate with KCNQ1, conferring distinct properties across various tissues. KCNQ1 activation requires membrane depolarization and phosphatidylinositol 4,5-bisphosphate (PIP2) whose cellular levels are controlled by Gq-coupled GPCR activation. While modulation of KCNQ1s voltage-dependent activation by KCNE1/3 is well-characterized, their effects on PIP2-dependent gating of KCNQ1 via GPCR signaling remain less understood. Here we resolved structures of KCNQ1-KCNE1 and reassessed reported KCNQ1-KCNE3 structures with and without PIP2. We revealed that KCNQ1-KCNE1/3 complexes feature two PIP2-binding sites, with KCNE1/3 contributing to a previously overlooked, uncharacterized site involving residues critical for voltage sensor and pore domain coupling. Via this site, KCNE1 and KCNE3 distinctly modulate the PIP2-dependent gating, in addition to the voltage sensitivity, of KCNQ1. Consequently, KCNE3 converts KCNQ1 into a voltage-insensitive PIP2-gated channel governed by GPCR signaling to maintain ion homeostasis in non-excitable cells. KCNE1, by significantly enhancing KCNQ1s PIP2 affinity and resistance to GPCR regulation, forms predominantly voltage-gated channels with KCNQ1 for conducting the slow-delayed rectifier current in excitable cardiac cells. Our study highlights how KCNE1/3 modulates KCNQ1 gating in different cellular contexts, providing insights for tissue-specifically targeting multi-functional channels.

biochemistry↗

bioRxiv2022

Crystal structures of bacterial Small Multidrug Resistance transporter EmrE in complex with structurally diverse substrates

Proteins from the bacterial small multidrug resistance (SMR) family are proton-coupled exporters of diverse antiseptics and antimicrobials, including polyaromatic cations and quaternary ammonium compounds. The transport mechanism of the Escherichia coli transporter, EmrE, has been studied extensively, but a lack of high-resolution structural information has impeded a structural description of its molecular mechanism. Here we apply a novel approach, multipurpose crystallization chaperones, to solve several structures of EmrE, including a 2.9 [A] structure at low pH without substrate. We report five additional structures in complex with structurally diverse transported substrates, including quaternary phosphonium, quaternary ammonium, and planar polyaromatic compounds. These structures show that binding site tryptophan and glutamate residues adopt different rotamers to conform to disparate structures without requiring major rearrangements of the backbone structure. Structural and functional comparison to Gdx-Clo, an SMR protein that transports a much narrower spectrum of substrates, suggests that in EmrE, a relatively sparse hydrogen bond network among binding site residues permits increased sidechain flexibility.

biochemistry↗