Plays an essential role in heart function and development by regulating the organization and function of the sarcoplasmic reticulum in cardiomyocytes. Monomer (heart including ventricles) (PubMed:32075961). Homodimer (atria, kidney, intestine); maybe disulfide-linked (PubMed:32075961). Homotrimer (heart, ventricle, skeletal muscle, liver) (PubMed:32075961). Interacts with ATL1 (PubMed:19665976). 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:24668814). Localizes to endoplasmic reticulum tubular network (PubMed:24668814). In cardiomyocytes, localizes to the junctional sarcoplasmic reticulum membrane which is closely tethered to the cell membrane and contractile machinery (PubMed:32075961). Highly expressed in heart including ventricles (at protein level). Expressed in cardiomyocytes (at protein level) (PubMed:32075961). Also, expressed in skeletal muscle and kidney and to a lesser extend in brain, liver and intestine (at protein level) (PubMed:32075961). 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. RNAi-mediated knockdown in the heart of P10 neonatal mice causes lethal cardiac dysfunction at 4 weeks (PubMed:19665976). Myocardium is disorganized with greater fibrotic regions with significant collagen deposition in the ventricular myocardium (PubMed:19665976). Mice show significant myocardial dilatation and cardiac contractile dysfunction (PubMed:19665976). Also, sarcomere organization is disordered and the sarcoplasmic reticulum membrane forms vacuoles (PubMed:19665976). Myocardium has elevated expression levels of ER stress marker Hspa5/Grp78, cleaved Casp12, Rtn4, Atl3 and Ckap4 (PubMed:19665976). Belongs to the DP1 family.