Ancillary protein that assembles as a beta subunit with a voltage-gated potassium channel complex of pore-forming alpha subunits. Modulates the gating kinetics and enhances stability of the channel complex. Assembled with KCNB1 modulates the gating characteristics of the delayed rectifier voltage-dependent potassium channel KCNB1 (PubMed:12954870). Associated with KCNC4/Kv3.4 is proposed to form the subthreshold voltage-gated potassium channel in skeletal muscle and to establish the resting membrane potential (RMP) in muscle cells (By similarity). Associated with KCNQ1/KCLQT1 may form the intestinal cAMP-stimulated potassium channel involved in chloride secretion that produces a current with nearly instantaneous activation with a linear current-voltage relationship (PubMed:21911611). Interacts with KCNB1 (PubMed:12954870). Interacts with KCNC2 (PubMed:14679187). Associates with KCNC4/Kv3.4 (By similarity). Interacts with KCNQ1; produces a current with nearly instantaneous activation with a linear current-voltage relationship and alters membrane raft localization (PubMed:21911611). Colocalizes with KCNB1 at high-density somatodendritic clusters on the surface of hippocampal neurons. Belongs to the potassium channel KCNE family.