Protein-export pathway illuminated

Two studies provide evidence that the protein complex PTEX is needed for export of malaria-parasite proteins into the cytoplasm of infected cells, and that such export is essential for parasite survival. See Letters p.587 & p.592 The malaria parasite, Plasmodium falciparum, infects and remodels the host's red blood cells, a process that requires the export of hundreds of proteins into the cytosol. This a considerable topological feat, as the parasite initially resides in a compartment known as the parasitophorous vacuole. A protein complex known as PTEX (Plasmodium translocon of exported proteins) was thought to be involved in this process, but evidence of function was circumstantial and indirect. Two reports in this issue of Nature use contrasting techniques to demonstrate that PTEX is essential for the export of malaria parasite proteins into the cytoplasm of infected cells, and that such export is essential for the parasite's life cycle. Brendan Elsworth et al. generated conditional mutants of PTEX components HSP101 and PTEX150, and show that when PTEX function is perturbed the export of proteins including the major virulence factor PfEMP1 is much reduced. Josh Beck et al. use an innovative dihydrofolate reductase based destabilization domain approach to inactivate the HSP101 and show that it is needed for the secretion of all classes of exported malarial proteins.