Lipid-transfer proteins in membrane trafficking at the Golgi complex

The Golgi complex (GC) represents the central junction for membrane trafficking. Protein and lipid cargoes continuously move through the GC in both anterograde and retrograde directions, departing to and arriving from diverse destinations within the cell. Nevertheless, the GC is able to maintain its identity and strict compartmentalisation, having a different composition in terms of protein and lipid content compared to other organelles. The discovery of coat protein complexes and the elucidation of their role in sorting cargo proteins into specific transport carriers have provided a partial answer to this phenomenon. However, it is more difficult to understand how relatively small and diffusible molecules like lipids can be concentrated in or excluded from specific subcellular compartments. The discovery of lipid-transfer proteins operating in the secretory pathway and specifically at the GC has shed light on one possible way in which this lipid compartmentalisation can be accomplished. The correct lipid distribution along the secretory pathway is of crucial importance for cargo protein sorting and secretion. This review focuses on what is now known about the putative and effective lipid-transfer proteins at the GC, and on how they affect the function and structure of the GC itself.