Pathway: Intra-Golgi traffic
Reactions in pathway: Intra-Golgi traffic :
Intra-Golgi traffic
The mammalian Golgi consists of at least three biochemically distinct cisternae, cis-, medial- and trans (reviewed in Szul and Sztul, 2011; Day et al, 2013). The structure and function of the Golgi are tightly interconnected, such that proteins that are required for protein transport through the Golgi are often also required for the organization of the Golgi stacks, and vice versa (reviewed in Liu and Storrie, 2012; Liu and Storrie, 2015; Chia and Gleeson, 2014; Munro, 2011). Newly synthesized proteins from the ER and ERGIC are received at the cis face of the Golgi and flow through to the trans-Golgi before being released to the trans-Golgi network (TGN) for further secretion to the endolysosomal system, plasma membrane or extracellular region. Retrograde flow from the trans- to cis-cisternae moves endocytosed cargo from the extracellular region, the plasma membrane and the endolysosomal system back towards the ER. Intra-Golgi retrograde traffic also returns resident Golgi proteins to their appropriate cisternae, in this way facilitating cisternal remodeling or maturation (reviewed in Boncompain and Perez, 2013; Day et al, 2013). Intra-Golgi traffic in both directions is mediated by COPI carriers, with specificity of transport being determined at least in part by the complement of SNAREs, RABs and tethering proteins involved (reviewed in Szul and Sztul, 2011; Spang 2013; Willet et al, 2013; Chia and Gleeson, 2014).
The secretory membrane system allows a cell to regulate delivery of newly synthesized proteins, carbohydrates, and lipids to the cell surface, a necessity for growth and homeostasis. The system is made up of distinct organelles, including the endoplasmic reticulum (ER), Golgi complex, plasma membrane, and tubulovesicular transport intermediates. These organelles mediate intracellular membrane transport between themselves and the cell surface. Membrane traffic within this system flows along highly organized directional routes. Secretory cargo is synthesized and assembled in the ER and then transported to the Golgi complex for further processing and maturation. Upon arrival at the trans Golgi network (TGN), the cargo is sorted and packaged into post-Golgi carriers that move through the cytoplasm to fuse with the cell surface. This directional membrane flow is balanced by retrieval pathways that bring membrane and selected proteins back to the compartment of origin.
The transit of proteins and other cargo through the cell requires a cellular transport process in which transported substances are moved in membrane-bounded vesicles. Transported substances are enclosed in the vesicle lumen or located in the vesicle membrane. The transport process begins with the formation of the vesicle itself, often triggered by the interaction of the cargo with the vesicle formation machinery. Vesicular transport pathways can include vesicle formation, coating, budding, uncoating and target membrane fusion depending upon the function of the pathway described. Vesicle-mediated transport occurs from within cell via ER and Golgi transport, as well as functioning in the endocytosis of material taken into the cell via scavenger receptors.