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:19219384). Associated with KCNH2/HERG is proposed to form the rapidly activating component of the delayed rectifying potassium current in heart (IKr). May associate with KCNQ2 and/or KCNQ3 and modulate the native M-type current. May associate with HCN1 and HCN2 and increase potassium current (By similarity). Interacts with KCNQ1; forms a heterooligomer complex leading to currents with an apparently instantaneous activation, a rapid deactivation process and a linear current-voltage relationship and decreases the amplitude of the outward current (By similarity). Interacts with KCNB1 (PubMed:19219384). Associates with KCNH2/ERG1 (By similarity). May associate with KCNQ2 and KCNQ3 (By similarity). Associates with HCN1 and probably HCN2 (PubMed:11420311). Heteromultimer with KCNC2. Interacts with KCNC2 (PubMed:14679187). Interacts with KCNQ1; forms a heterooligomer complex that targets to the membrane raft and leading to currents with an apparently instantaneous activation, a rapid deactivation process and a linear current-voltage relationship and decreases the amplitude of the outward current (By similarity). Colocalizes with KCNB1 at the plasma membrane. Expressed in the heart (PubMed:19219384). Belongs to the potassium channel KCNE family.