Mechanisms of transport through the Golgi complex

Abstract

The Golgi complex is the central sorting and processing station of the secretory pathway, ensuring that cargo proteins, which are synthesized in the endoplasmic reticulum, are properly glycosylated and packaged into carriers for transport to their final destinations. Two recent studies highlight the fact that properties of membrane lipids play key roles in Golgi structural organization and trafficking. The Antonny laboratory has demonstrated the mechanism by which a Golgi tether containing a membrane-curvature-sensing domain at one end can link highly curved and flat membranes together in a reversible manner. In this way, a strong interaction that binds membranes together in an oriented fashion can easily be disrupted as the properties of the membranes change. The Lippincott-Schwartz laboratory has developed a new model for intra-Golgi trafficking, called the rapid-partitioning model, which incorporates lipid trafficking as an integral part. Simulations reveal that the sorting of lipids into processing and export domains that are connected to each Golgi cisterna, and bidirectional trafficking throughout the Golgi to allow proteins to associate with their preferred lipid environment, is sufficient to drive protein transport through the secretory pathway. Although only a proof in principle, this model for the first time invokes lipid sorting as the driving force in intra-Golgi trafficking, and provides a framework for future experimental work.

Organizational Interplay of Golgi N-Glycosyltransferases Involves Organelle Microenvironment-Dependent Transitions between Enzyme Homo- and Heteromers

“…Thus, complex formation itself appears to neither restrict intra-Golgi transport nor their recycling between the Golgi and the ER. Therefore, the formation of glycosyltransferase complexes is fully compatible with the "cisternal maturation" or the "rapid partitioning" models, which both entail that the cisternal contents change both laterally and along the cis-trans axis of the Golgi stack (29,30,50,51). The data are also compatible with the suggested recycling of the Golgi glycosyltransferases between the Golgi and the ER (42).…”

Cosmc is an essential chaperone for correct protein O-glycosylation

“…Because mouse ES cells are male and hemizygous for Cosmc, we could use these cells to examine the consequences of complete Cosmc loss on protein glycosylation. The complex biosynthesis of glycoproteins requires the activities of many dozens of enzymes in the ER, Golgi, and other organelles in the secretory pathway, including nucleotide sugar transporters, glycosidases, glycosyltransferases, and other chaperones involved in glycoprotein assembly and movement to the cell surface (22)(23)(24)(25)(26). We found that although mouse ES cells with a null Cosmc lack T-synthase activity and express Tn antigen, all other protein glycosylation, including total N-glycan profiles by mass spectrometry, and cell growth appeared normal in vitro.…”

The Golgi apparatus: insights from filamentous fungi

“…Various observations have suggested that the Golgi apparatus is a dynamic organelle with self-organizing properties, maintained in a dynamic state by continuous input of energy (Jackson 2009). Various lines of evidence indicate that this is also true in A. nidulans.…”