title: A Lipolytic Lecithin:Cholesterol Acyltransferase Secreted by Toxoplasma Facilitates Parasite Replication and Egress.
abstract: The protozoan parasite Toxoplasma gondii develops within a parasitophorous vacuole (PV) in mammalian cells, where it scavenges cholesterol. When cholesterol is present in excess in its environment, the parasite expulses this lipid into the PV or esterifies it for storage in lipid bodies. Here, we characterized a unique T. gondii homologue of mammalian lecithin:cholesterol acyltransferase (LCAT), a key enzyme that produces cholesteryl esters via transfer of acyl groups from phospholipids to the 3-OH of free cholesterol, leading to the removal of excess cholesterol from tissues. TgLCAT contains a motif characteristic of serine lipases "AHSLG" and the catalytic triad consisting of serine, aspartate, and histidine (SDH) from LCAT enzymes. TgLCAT is secreted by the parasite, but unlike other LCAT enzymes it is cleaved into two proteolytic fragments that share the residues of the catalytic triad and need to be reassembled to reconstitute enzymatic activity. TgLCAT uses phosphatidylcholine as substrate to form lysophosphatidylcholine that has the potential to disrupt membranes. The released fatty acid is transferred to cholesterol, but with a lower transesterification activity than mammalian LCAT. TgLCAT is stored in a subpopulation of dense granule secretory organelles, and following secretion, it localizes to the PV and parasite plasma membrane. LCAT-null parasites have impaired growth in vitro, reduced virulence in animals, and exhibit delays in egress from host cells. Parasites overexpressing LCAT show increased virulence and faster egress. These observations demonstrate that TgLCAT influences the outcome of an infection, presumably by facilitating replication and egress depending on the developmental stage of the parasite.
authors.affiliation: From the Department of Molecular Microbiology and Immunology, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205, the Molecular Parasitology Section, Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Viviana
authors.initials: V
authors.lastname: Pszenny
authors.affiliation: From the Department of Molecular Microbiology and Immunology, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205.
authors.forename: Karen
authors.initials: K
authors.lastname: Ehrenman
authors.affiliation: From the Department of Molecular Microbiology and Immunology, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205.
authors.forename: Julia D
authors.initials: JD
authors.lastname: Romano
authors.affiliation: the Molecular Parasitology Section, Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kennard
authors.affiliation: the Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109, and.
authors.forename: Aric
authors.initials: A
authors.lastname: Schultz
authors.affiliation: the Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: David S
authors.initials: DS
authors.lastname: Roos
authors.affiliation: the Molecular Parasitology Section, Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Grigg
authors.affiliation: the Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109, and.
authors.forename: Vern B
authors.initials: VB
authors.lastname: Carruthers
authors.affiliation: From the Department of Molecular Microbiology and Immunology, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205, icoppens@jhsph.edu.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Coppens
mesh_terms: D020134:Catalytic Domain; D002460:Cell Line; D006801:Humans; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014122:Toxoplasma / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D014123:Toxoplasmosis / Q000201:enzymology* / Q000235:genetics / Q000473:pathology
chemical_list: D015800:Protozoan Proteins; D007862:Phosphatidylcholine-Sterol O-Acyltransferase
keywords: Phospholipase A; Toxoplasma gondii; cell surface enzyme; host-pathogen interaction; parasitology