title: TgSUB2 is a Toxoplasma gondii rhoptry organelle processing proteinase.
abstract: 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.
authors.affiliation: Departments of Medicine and of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx NY 10461, USA.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Miller
authors.forename: Vandana
authors.initials: V
authors.lastname: Thathy
authors.forename: James W
authors.initials: JW
authors.lastname: Ajioka
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Blackman
authors.forename: Kami
authors.initials: K
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D015388:Organelles; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013381:Subtilisins; D014122:Toxoplasma / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D008565:Membrane Proteins; D015800:Protozoan Proteins; C117001:ROP 1 protein, Toxoplasma gondii; D012697:Serine Endopeptidases; D013381:Subtilisins