Characterization of an early-diverging KCNE potassium-channel auxiliary subunit in the jawless vertebrate lamprey.

Abstract

The KCNE (KCNE1-6) proteins are single-pass transmembrane auxiliary subunits of the voltage-gated K⁺ channel KCNQ1. KCNQ1-KCNE complexes have been well studied in jawed vertebrates ranging from zebrafish to humans, but KCNE subunits from earlier-diverging vertebrates remain poorly characterized. Here, we functionally characterize a single KCNE-like gene in lamprey, a jawless vertebrate, and designate it <i>kcne0</i> as an early-diverging member of the KCNE family. KCNE0 shows moderate amino acid sequence similarity to KCNE1-6 but is not particularly similar to any single isoform. Both <i>kcnq1</i> and <i>kcne0</i> transcripts were detected in multiple lamprey organs. When co-expressed with lamprey KCNQ1, KCNE0 produced a constitutively active current, similar to KCNE3. By contrast, KCNE0 modulated KCNQ1 from other species less effectively, suggesting species-specific tuning of KCNQ1-KCNE compatibility. Introducing into KCNE0 an intracellular tetra-leucine motif analogous to that in KCNE4 markedly reduced KCNQ1 current amplitude, conferring a KCNE4-like inhibitory effect. Overall, this work provides a functional reference for comparing KCNE-dependent modulation of KCNQ1 across vertebrates and suggests an underlying compatibility mechanism.