title: Functional analysis of Toxoplasma gondii protease inhibitor 1.
abstract: We have characterized a Kazal family serine protease inhibitor, Toxoplasma gondii protease inhibitor 1 (TgPI-1), in the obligate intracellular parasite Toxoplasma gondii. TgPI-1 contains four inhibitor domains predicted to inhibit trypsin, chymotrypsin, and elastase. Antibodies against recombinant TgPI-1 detect two polypeptides, of 43 and 41 kDa, designated TgPI-1(43) and TgPI-1(41), in tachyzoites, bradyzoites, and sporozoites. TgPI-1(43) and TgPI-1(41) are secreted constitutively from dense granules into the excreted/secreted antigen fraction as well as the parasitophorous vacuole that T. gondii occupies during intracellular replication. Recombinant TgPI-1 inhibits trypsin, chymotrypsin, pancreatic elastase, and neutrophil elastase. Immunoprecipitation studies with anti-rTgPI-1 antibodies reveal that recombinant TgPI-1 forms a complex with trypsin that is dependent on interactions with the active site of the protease. TgPI-1 is the first anti-trypsin/chymotrypsin inhibitor to be identified in bradyzoites and sporozoites, stages of the parasite that would be exposed to proteolytic enzymes in the digestive tract of the host.
authors.affiliation: The W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland 21205, USA.
authors.forename: Meredith Teilhet
authors.initials: MT
authors.lastname: Morris
authors.forename: Alexandra
authors.initials: A
authors.lastname: Coppin
authors.forename: Stanislas
authors.initials: S
authors.lastname: Tomavo
authors.forename: Vern B
authors.initials: VB
authors.lastname: Carruthers
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005089:Exocytosis / Q000502:physiology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000469:parasitology; D006801:Humans; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015842:Serine Proteinase Inhibitors / Q000235:genetics / Q000378:metabolism*; D014122:Toxoplasma / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D014357:Trypsin / Q000378:metabolism
chemical_list: D015800:Protozoan Proteins; D011994:Recombinant Proteins; D015842:Serine Proteinase Inhibitors; C412510:TgPI protein, Toxoplasma gondii; D014357:Trypsin; D002118:Calcium