Plays an essential role in heart function and development by regulating the organization and function of the sarcoplasmic reticulum in cardiomyocytes. Monomer (heart, ventricle). Homodimer (atria, kidney, intestine); maybe disulfide-linked. Homotrimer (heart, ventricle, skeletal muscle, liver). Interacts with ATL1. Interacts with ATL2. Interacts with ATL3. Interacts with CKAP4. Interacts with RTN4. Interacts with ZFYVE27. Localizes to endoplasmic reticulum tubular network. In cardiomyocytes, localizes to the junctional sarcoplasmic reticulum membrane which is closely tethered to the cell membrane and contractile machinery. The short lumenal loops between transmembrane domains 1 and 2 and between transmembrane domains 3 and 4 may impart a wedge-like configuration, thus deforming membranes. Belongs to the DP1 family.