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Eukaryotic Cell doi:10.1128/EC.00081-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A thioredoxin family protein of the apicoplast periphery identifies abundant candidate transport vesicles in Toxoplasma

Seattle Biomedical Research Institute, 307 Westlake Ave. N., Seattle, WA 98109, USA; Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, 615 N. Wolfe Street, Baltimore, MD 21205, USA; Interdisciplinary Program in Pathobiology, Department of Global Health, University of Washington, Seattle, WA 98195, USA; and Department of Microbiology, Immunology, and Molecular Genetics, 609 Charles E. Young Dr. East, University of California, Los Angeles, CA, 90095, USA

^* To whom correspondence should be addressed. Email: marilyn.parsons{at}sbri.org.

	Abstract

Toxoplasma gondii, which causes toxoplasmic encephalitis and birth defects, contains an essential chloroplast-related organelle to which proteins are trafficked via the secretory system. This organelle, the apicoplast, is bounded by multiple membranes. In this report we identify a novel apicoplast-associated thioredoxin family protein, ATrx1, which is predominantly soluble or peripherally associated with membranes, and which localizes primarily to the outer compartments of the organelle. As such, it represents the first protein to be identified as residing in the apicoplast intermembrane spaces. ATrx1 lacks the apicoplast targeting sequences typical of luminal proteins. However, sequences near the N-terminus are required for proper targeting of ATrx1, which is proteolytically processed from a larger precursor to multiple smaller forms. This protein reveals a population of vesicles, hitherto unrecognized as being highly abundant in the cell, which may serve to transport proteins to the apicoplast.