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Infection and Immunity, November 2008, p. 4865-4875, Vol. 76, No. 11
0019-9567/08/$08.00+0     doi:10.1128/IAI.00782-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Intervacuolar Transport and Unique Topology of GRA14, a Novel Dense Granule Protein in Toxoplasma gondii{triangledown}

Michael E. Rome,1 Josh R. Beck,1 Jay M. Turetzky,1 Paul Webster,2 and Peter J. Bradley1*

Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, Los Angeles, California 90095-1489,1 Ahmanson Advanced Electron Microscopy and Imaging Center, House Ear Institute, Los Angeles, California 900572

Received 20 June 2008/ Returned for modification 23 July 2008/ Accepted 18 August 2008

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 PV membrane (PVM). Only a small portion of the protein constituents of the dense granules have been identified, and little is known regarding their roles 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 disrupted GRA14 and exploited the knockout strain to show that GRA14 can be transferred between vacuoles in a coinfection 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 both for the trafficking of GRA proteins to their ultimate destinations and for expectations of functional domains of GRA proteins at the host-parasite interface.

* Corresponding author. Mailing address: Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, Los Angeles CA 90095-1489. Phone: (310) 825-8386. Fax: (310) 825-5231. E-mail: pbradley{at}ucla.edu

{triangledown} Published ahead of print on 2 September 2008.

Editor: W. A. Petri, Jr.

Infection and Immunity, November 2008, p. 4865-4875, Vol. 76, No. 11
0019-9567/08/$08.00+0     doi:10.1128/IAI.00782-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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