Enables transmembrane transporter binding activity. Involved in endoplasmic reticulum calcium ion homeostasis; endoplasmic reticulum unfolded protein response; and negative regulation of apoptotic process. Located in endoplasmic reticulum. Orthologous to human HERPUD1 (homocysteine inducible ER protein with ubiquitin like domain 1). [provided by Alliance of Genome Resources, Apr 2022]