TgSUB2 is a Toxoplasma gondii rhoptry organelle processing proteinase

Authors

  • Steven A. Miller,

    1. Departments of Medicine and of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx NY 10461, USA.
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    • S.A.M. and V.T. contributed equally to this work.

  • Vandana Thathy,

    1. Departments of Medicine and of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx NY 10461, USA.
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    • S.A.M. and V.T. contributed equally to this work.

  • James W. Ajioka,

    1. Department of Pathology, Cambridge University, Cambridge, UK.
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  • Michael J. Blackman,

    1. Division of Parasitology, National Institute for Medical Research, Mill Hill, London NW7 1AA, UK.
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  • Kami Kim

    Corresponding author
    1. Departments of Medicine and of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx NY 10461, USA.
      E-mail kkim@aecom.yu.edu; Tel. (+1) 718 430 2611; Fax (+1) 718 430 8968.
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E-mail kkim@aecom.yu.edu; Tel. (+1) 718 430 2611; Fax (+1) 718 430 8968.

Summary

All parasites in the phylum Apicomplexa, including Toxoplasma gondii and Plasmodium falciparum, contain rhoptries, specialized secretory organelles whose contents are thought to be essential for successful invasion of host cells. Serine proteinase inhibitors have been reported to block host cell invasion by both T. gondii and P. falciparum. We describe the cloning and characterization of TgSUB2, a subtilisin-like serine proteinase, from T. gondii. Like its closest homologue P. falciparum PfSUB-2, TgSUB2 is predicted to be a type I transmembrane protein. Disruption of TgSUB2 was unsuccessful implying that TgSUB2 is an essential gene. TgSUB2 undergoes autocatalytic processing as it traffics through the secretory pathway. TgSUB2 localizes to rhoptries and associates with rhoptry protein ROP1, a potential substrate. A sequence within TgSUB2 with homology to the ROP1 cleavage site (after Glu) was identified and mutated by site-directed mutagenesis. This mutation abolished TgSUB2 autoprocessing suggesting that TgSUB2 is a rhoptry protein maturase with similar specificity to the ROP1 maturase. Processing of secretory organelle contents appears to be ubiquitous among the Apicomplexa. As subtilases are present in genomes of all the Apicomplexa sequenced to date, subtilases may represent a novel chemotherapeutic target.

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