Cytoplasmic potassium channel subunit that modulates the characteristics of the channel-forming alpha-subunits (PubMed:10594054). Contributes to the regulation of nerve signaling, and prevents neuronal hyperexcitability (By similarity). Promotes expression of the pore-forming alpha subunits at the cell membrane, and thereby increases channel activity (By similarity). Promotes potassium channel closure via a mechanism that does not involve physical obstruction of the channel pore (By similarity). Promotes KCNA4 channel closure (By similarity). Modulates the functional properties of KCNA5 (By similarity). Enhances KCNB2 channel activity (By similarity). Binds NADPH and has NADPH-dependent aldoketoreductase activity (By similarity). Has broad substrate specificity and can catalyze the reduction of methylglyoxal, 9,10-phenanthrenequinone, prostaglandin J2, 4-nitrobenzaldehyde, 4-nitroacetophenone and 4-oxo-trans-2-nonenal (in vitro) (By similarity). Forms heteromultimeric complex with alpha subunits. Recruited to the cytoplasmic side of the cell membrane via its interaction with pore-forming potassium channel alpha subunits. Associates with microtubules when unphosphorylated. Expression first detected in somites at embryonic stage 24 (26 hours). At stage 29 (35 hours), expression is detected in the spinal cord. In stage 30 embryos (36 hours), expression is down-regulated in somites and up-regulated in spinal cord. By stage 35-36 (50 hours), expression is limited to dorsal spinal neurons of the spinal cord. In contrast to KCNAB1, the shorter N-terminal domain of KCNAB2 cannot mediate closure of delayed rectifier potassium channels by physically obstructing the pore. Belongs to the shaker potassium channel beta subunit family.