Promotes cell surface expression of the potassium channel KCND2. Modulates the activity and gating characteristics of the potassium channel KCND2. Has no dipeptidyl aminopeptidase activity. 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. Predominantly expressed in the brain. Isoform DPPX-L is expressed exclusively in the brain whereas isoform DPPX-S is found in brain, kidney, ovary and testis. N-glycosylated. Belongs to the peptidase S9B family.