Shelters ceramides and diacylglycerol lipids inside its START domain and mediates the intracellular trafficking of ceramides and diacylglycerol lipids in a non-vesicular manner (PubMed:19005213). N-hexadecanoylsphing-4-enine(in) = N-hexadecanoylsphing-4-enine(out) Interacts with VAPA and VAPB. Interaction with VAPB is less efficient than with VAPA. Interacts (via FFAT motif) with the MOSPD2 (via MSP domain). Preferentially localized to the Golgi apparatus. The START domain recognizes ceramides and diacylglycerol lipids, interacts with membranes, and mediates the intermembrane transfer of ceramides and diacylglycerol lipids. The PH domain targets the Golgi apparatus. The FFAT motif is required for interaction with VAPA, VAPB and MOSPD2. Phosphorylation on Ser-132 decreases the affinity toward phosphatidylinositol 4-phosphate at Golgi membranes and reduces ceramide transfer activity (By similarity). Inactivated by hyperphosphorylation of serine residues by CSNK1G2/CK1 that triggers dissociation from the Golgi complex, thus down-regulating ER-to-Golgi transport of ceramide and sphingomyelin synthesis (PubMed:19005213).