Plays an essential role in heart function and development by regulating the organization and function of the sarcoplasmic reticulum in cardiomyocytes. Monomer (PubMed:32075961). Homodimer; maybe disulfide-linked (PubMed:32075961). Homotrimer (By similarity). Interacts with ATL1 (By similarity). Interacts with ATL2 (PubMed:19665976). Interacts with ATL3 (PubMed:32075961). Interacts with CKAP4 (PubMed:32075961). Interacts with RTN4 (isoforms A and B) (PubMed:32075961). Interacts with ZFYVE27 (PubMed:23969831). Localizes to endoplasmic reticulum tubular network (PubMed:23969831). In cardiomyocytes, localizes to the junctional sarcoplasmic reticulum membrane which is closely tethered to the cell membrane and contractile machinery (By similarity). Expressed in heart (at protein level) (PubMed:32075961). Expressed in circumvallate papillae and testis (PubMed:16720576). 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.