Regulation and Coordination of Intracellular Trafficking: An Overview
Julie G. Donaldson and Nava Segev
During the last two decades, efforts in the protein trafficking field have focused primarily on the identification of the machinery components of vesicular transport and mechanisms that underlie it. In addition, research has started to reveal how intra-cellular trafficking is regulated. Here, we summarize the current state of our knowledge about the regulation of vesicular transport and its coordination with other cellular processes. At the most basic level, individual transport steps are regulated spatially and temporally in two different ways. First, molecular switches of the Arf, Rab and Rho GTPase families regulate the assembly of components of the vesicular transport machinery on membranes, mediating the formation, targeting and fusion of vesicles that shuttle cargo between intra-cellular compartments. Second, reversible post-translational modifications, like phosphorylation and ubiquitination, allow efficient cargo sorting and machinery component recycling. At a higher level, individual transport steps are integrated into whole pathways, with GTPases as a mechanism for this integration. Finally, intra-cellular trafficking pathways are coordinated with other cellular processes. Here too, GTPases appear to play a role by orchestrating coordination.