Promotes cell surface expression of the potassium channel KCND2 (PubMed:22311982). Modulates the activity and gating characteristics of the potassium channel KCND2 (PubMed:22311982). Has no dipeptidyl aminopeptidase activity (By similarity). Homodimer (in vitro). Interacts with KCND2. Identified in a complex with KCND2 and KCNIP2. Forms an octameric complex composed of four DPP6 subunits bound to the KCND2 tetramer. Detected in brain cortex (at protein level). N-glycosylated. Knockdown animals obtained using siRNA technology have smaller brains than their wild-type littermates. Performance on the standard Morris water maze indicated spatial memory defects and learning disabilities. Belongs to the peptidase S9B family.