Endoplasmic reticulum cargo receptor that mediates the export of lipoproteins by recruiting cargos into COPII vesicles to facilitate their secretion. Acts as a cargo receptor for lipoproteins bearing both APOB and APOA1, thereby regulating lipoprotein delivery and the maintenance of lipid homeostasis. Cycles between the endoplasmic reticulum and the Golgi. The di-lysine motif confers endoplasmic reticulum localization for type I membrane proteins. Belongs to the SURF4 family.