Transmembrane channel-like 4 (TMC4) could act as a negative regulator of KCNQ1 (Kv7.1) potassium channel

TMC4 is a member of the transmembrane channel-like (TMC) protein family. In this family, TMC1 and TMC2 are thought to form the mechano-electrical transduction (MET) channel in the inner ear. On the other hand, the intrinsic functions of the other TMC family members (TMC3-8) are largely unknown. KCNQ1 (Kv7.1) channel is a voltage-gated potassium channel and plays crucial physiological roles with its auxiliary subunits, KCNE proteins (e.g. KCNQ1/KCNE1 complex contributes to cardiac repolarization, and KCNQ1/KCNE3 complex participates in epithelial ion transport). Recently, it was reported that TMC1 and TMC2 interacted with KCNQ1 and suppressed its K⁺ currents. However, the relationships between KCNQ1 and the other TMC proteins have not been examined. Here, we show a novel interaction and a functional association between overexpressed TMC4 and KCNQ1. The Bead Halo assay and FRET analysis revealed the physical interaction between these two proteins. Whole-cell patch clamp recording demonstrated that co-expression of TMC4 reduced KCNQ1 current densities without altering their voltage dependence and activation kinetics. This effect was also observed in the KCNQ1/KCNE1 and KCNQ1/KCNE3 channel complexes. A structural prediction using AlphaFold-Multimer suggested possible interaction sites between TMC4 and KCNQ1. Mutageneses, followed by patch clamp recording, suggested that specific amino acid residues at these sites contribute to the inhibitory effect of TMC4. These results indicate that TMC4 could function as a negative regulator of the KCNQ1 channel. Our findings could enhance the understanding of KCNQ1 channel regulation and propose potential research directions on the function of TMC4 under various physiological and pathological conditions.