The 56th Annual Meeting and Symposium of the Society of General Physiologists Trafficking of Transporters

In addition to their direct catalytic role, the proper function of transport proteins depends on multiple cellular processes to ensure: that the protein is folded and assembled into its correct conformation; that misfolded proteins are degraded; that the protein is targeted to its correct location within the cell; that the copy number of the protein is maintained by regulated synthesis and turnover; and that any other proteins involved in the transport process, whether it be subunits in a macro-molecular complex or proteins in other membrane domains , are present in sufficient number and in the correct location(s). The importance of membrane protein processing and targeting for normal cellular and body function has become abundantly clear over the past decade , as an increasing number of genetic " transport " diseases, with cystic fibrosis being the proto-typical example , turn out to be due to disrupted protein trafficking (compare M. Aridor and L.A. Hannan. 2000. Traffic. 1:836–851 and 3:781–790). Likewise, a remarkable generality of the underlying processes is emerging—in the sense that the targeting signals and trafficking machinery are conserved evolutionarily and among different cells. The recent advances in elucidating the mechanisms underlying protein trafficking were the focus of the organized the symposium on Trafficking of Transporters , which highlighted the recent progress that has taken place in this important field. With 150 participants , and 82 invited and poster presentations covering a broad range of topics, the meeting was lively and the major issues were put in perspective. Intracellular protein traffic occurs by vesicular transport between different organellar membrane compartments as well as between organellar membranes and the plasma membrane (Fig. 1). After their initial synthesis and assembly in the endo-plasmic reticulum (ER), membrane proteins are passed on to the Golgi stack, from which they may be retrieved back to the ER. The main route, however, is through the Golgi stack on to the plasma membrane, where the proteins' destinies are determined by specific targeting signals. Once in the plasma membrane, the proteins are retrieved by endocytosis to the endocytic recycling compartment from which they may be returned to the plasma membrane—either directly or via the Golgi stack—or targeted for destruction in the lysosomes. Because membrane protein trafficking occurs by vesicular transport, many questions relating to the protein trafficking eventually become questions about the mechanisms underlying the sequestration of proteins into the appropriate population of transport vesicles. Two key steps …