Potential role in vesicular protein trafficking, mainly in the early secretory pathway. Required for the maintenance of the Golgi apparatus; involved in protein exchange between Golgi stacks during assembly. Probably not required for COPI-vesicle-mediated retrograde transport. Interacts with TMED9 and TMED10. Probably cycles between compartments of the early secretatory pathway. Belongs to the EMP24/GP25L family.