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. Synergizes with the GTPase SAR1B to mediate transport of circulating lipoproteins. Promotes the secretion of PCSK9. Also mediates the efficient secretion of erythropoietin (EPO). May also play a role in the maintenance of the architecture of the endoplasmic reticulum-Golgi intermediate compartment and of the Golgi. Found in a complex composed at least of SURF4, TMED2 and TMED10 (By similarity). May interact with LMAN1 (By similarity). Interacts with ZFYVE27 and with KIF5A in a ZFYVE27-dependent manner (PubMed:21976701). Interacts with STING1 (By similarity). Interacts with SAR1B (By similarity). Interacts with TMEM41B (By similarity). Cycles between the endoplasmic reticulum and the Golgi. The di-lysine motif confers endoplasmic reticulum localization for type I membrane proteins. Embryonic lethality between 3.5 and 9.5 dpc (PubMed:31978056). Conditional deletion in the liver depletes plasma lipids and protects mice from atherosclerosis (PubMed:33186557). Belongs to the SURF4 family.