Co-immunoprecipitation assays of heterologously expressed TMEM163, ZNT1, ZNT2, ZNT3, and ZNT4 proteins. Co-expressions of TMEM163-DDK with ZNT1-HA, ZNT2-HA, and TMEM163-HA show heterodimerization as indicated by their respective eluted bands upon immunoblotting with A) anti-DDK monoclonal antibody (mAb) and B) anti-HA polyclonal antibody (pAb). Co-expressions of TMEM163-DDK with ZNT2-HA, and TMEM163-HA with ZNT4-DDK both show heterodimerization as indicated by their respective eluted bands upon immunoblotting with C) anti-DDK mAb and D) anti-HA pAb. Expression of TMEM163-HA or TMEM163-DDK in all trials serves as a positive (dimerization) control with itself, while single expressions of each respective protein serve as negative controls. L, protein ladder; I, input/cell lysate; E, elution; +, expressed; –, not expressed. Predicted molecular weight (MW) of human proteins: TMEM163 = 31.5 kDa, ZNT1 = 55.3–63.0 kDa, ZNT2 variant 2 = 35.0 kDa, ZNT3 = 41.8 kDa, and ZNT4 = 47.4 kDa. The images are representative of N ≥ 6 independent trials.