The cathepsin B of Toxoplasma gondii, toxopain-1, is critical for parasite invasion and rhoptry protein processing

Xuchu Que, Huân Ngô, Jeffrey Lawton, Mary Gray, Qing Liu, Juan Engel, Linda Brinen, Partho Ghosh, Keith A Joiner, Sharon L. Reed

Research output: Contribution to journalArticle

77 Scopus citations


Cysteine proteinases play a major role in invasion and intracellular survival of a number of pathogenic parasites. We cloned a single copy gene, tgcpl, from Toxoplasma gondii and refolded recombinant enzyme to yield active proteinase. Substrate specificity of the enzyme and homology modeling identified the proteinase as a cathepsin B. Specific cysteine proteinase inhibitors interrupted invasion by tachyzoites. The T. gondii cathepsin B localized to rhoptries, secretory organelles required for parasite invasion into cells. Processing of the pro-rhoptry protein 2 to mature rhoptry proteins was delayed by incubation of extracellular parasites with a cathepsin B inhibitor prior to pulse-chase immunoprecipitation. Delivery of cathepsin B to mature rhoptries was impaired in organisms with disruptions in rhoptry formation by expression of a dominant negative μ1-adaptin. Similar disruption of rhoptry formation was observed when infected fibroblasts were treated with a specific inhibitor of cathepsin B, generating small and poorly developed rhoptries. This first evidence for localization of a cysteine proteinase to the unusual rhoptry secretory organelle of an apicomplexan parasite suggests that the rhoptries may be a prototype of a lysosome-related organelle and provides a critical link between cysteine proteinases and parasite invasion for this class of organism.

Original languageEnglish (US)
Pages (from-to)25791-25797
Number of pages7
JournalJournal of Biological Chemistry
Issue number28
Publication statusPublished - Jul 12 2002
Externally publishedYes


ASJC Scopus subject areas

  • Biochemistry

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