Potential role in vesicular protein trafficking, mainly in the early secretory pathway. Contributes to the coupled localization of TMED2 and TMED10 in the cis-Golgi network (By similarity). Monomer in endoplasmic reticulum, endoplasmic reticulum-Golgi intermediate compartment and cis-Golgi network. Interacts (via C-terminus) with COPG1; the interaction involves dimeric TMED3; however, there are conflicting reports on the interaction. Interacts with GORASP1 and GORASP2 (By similarity). Probably cycles between compartments of the early secretatory pathway. Belongs to the EMP24/GP25L family.