Intervacuolar transport and unique topology of GRA14, a novel dense granule protein in Toxoplasma

Infect Immun. 2008 Sep 2. [Epub ahead of print]

Intervacuolar transport and unique topology of GRA14, a novel dense granule protein in Toxoplasma gondii

Rome ME, Beck JR, Turetzky JM, Webster P, Bradley PJ.

Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, Los Angeles CA 90095-1489 USA; Ahmanson Advanced Electron Microscopy and Imaging Center, House Ear Institute, Los Angeles, CA 90057 USA.

Toxoplasma gondii is an obligate intracellular parasite that resides in the cytoplasm of its host in a unique membrane-bound vacuole known as the parasitophorous vacuole (PV). The membrane surrounding the parasite is remodeled by the dense granules, secretory organelles that release an array of proteins into the vacuole and to the parasitophorous vacuole membrane (PVM). Only a small portion of the protein constituents of the dense granules have been identified and little is known regarding their role in infection or how they are trafficked within the infected host cell. In this report, we identify a novel secreted dense granule protein, GRA14, and show that it is targeted to membranous structures within the vacuole known as the intravacuolar network and to the vacuolar membrane surrounding the parasite. We have disrupted GRA14 and exploited the knockout strain to show that GRA14 can be transferred between vacuoles in a co-infection experiment with wild type parasites. We also show that GRA14 has an unexpected topology in the PVM with its C-terminus facing the host cytoplasm and its N-terminus facing the vacuolar lumen. These findings have important implications for both the trafficking of GRA proteins to their ultimate destination and for expectations of functional domains of GRA proteins at the host-parasite interface.

PMID: 18765740 [PubMed - as supplied by publisher]