Ypt/Rab GTPases: Regulators of Protein Trafficking

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Science's STKE  18 Sep 2001:
Vol. 2001, Issue 100, pp. re11
DOI: 10.1126/stke.2001.100.re11

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In eukaryotic cells, an evolutionarily conserved transport system routes proteins through a number of highly regulated pathways. In these pathways, intercellular signaling proteins are released, receptors and transporters are presented on the outer cell membrane, and ligand-bound receptors are internalized. Therefore, the protein transport system is central to the interaction of cells with their environments. The passage of proteins through this transport system involves an orderly progression through a series of membrane-bound compartments. To be transported from one compartment to the next, proteins are packaged into small vesicles that bud from one compartment and fuse with the next. Like traffic lights at critical intersections, a family of proteins known as Ypt/Rab guanosine triphosphatases (GTPases) regulates vesicle formation, movement, attachment, and fusion at each transport step. These individual transport steps might be further coordinated by Ypt/Rabs through their communication with each other. GTPases in general serve as molecular switches that can be turned "on" or "off" by upstream regulators. Ypt/Rabs transmit their "on" signals through the recruitment and activation of multiple downstream effector proteins, which carry out the various functions necessary for vesicle transport. Numerous regulators and effectors of Ypt/Rab GTPases have been identified, leading to models that predict how they carry out their functions. This review summarizes the current knowledge about molecular mechanisms by which the Ypt/Rab switches perform their highly complex task.