title: Molecular characterization of TgMIC5, a proteolytically processed antigen secreted from the micronemes of Toxoplasma gondii.
abstract: During invasion of host cells, Toxoplasma gondii discharges the contents of small, apically located secretory organelles called micronemes. Micronemal proteins are known to be necessary for both parasite motility and invasion of host cells. To further define the contents of Toxoplasma micronemes, we used cell fractionation and secretion-modulating drugs to identify six novel, putative micronemal proteins. In this paper we describe preliminary characterization of one of these novel proteins, TgMIC5. Molecular cloning and DNA sequence analysis of the TgMIC5 cDNA and gene revealed that it encodes a previously identified immunodominant antigen called H4. TgMIC5 also possesses a consensus sequence unique to members of the parvulin family of peptidyl-prolyl cis-trans isomerases (PPIases). TgMIC5 is expressed as a preproprotein, which is proteolytically processed to a proprotein by signal peptidase before being further processed to a mature protein of 22 kDa. Using a combination of protein secretion experiments, immunofluorescence and immunoelectron microscopy, we demonstrated that TgMIC2 is stored in the micronemes of T. gondii tachyzoites before it is secreted into the surrounding medium. Based on its homology with parvulin-like PPIases, TgMIC5 may assist in the folding of other micronemal proteins that function in invasion of host cells by T. gondii tachyzoites.
authors.affiliation: The W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins University School of Hygiene and Public Health, 615 N. Wolfe Street, Baltimore, MD 21205, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Brydges
authors.forename: G D
authors.initials: GD
authors.lastname: Sherman
authors.forename: S
authors.initials: S
authors.lastname: Nockemann
authors.forename: A
authors.initials: A
authors.lastname: Loyens
authors.forename: W
authors.initials: W
authors.lastname: Däubener
authors.forename: J F
authors.initials: JF
authors.lastname: Dubremetz
authors.forename: V B
authors.initials: VB
authors.lastname: Carruthers
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D001483:Base Sequence; D003001:Cloning, Molecular; D019084:Fluorescent Antibody Technique, Indirect; D015723:Gene Library; D017125:Genes, Protozoan; D018503:Genome, Protozoan; D016056:Immunodominant Epitopes / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D022142:Secretory Vesicles / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D014122:Toxoplasma / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D000953:Antigens, Protozoan; C417762:H4 protein, Toxoplasma gondii; D016056:Immunodominant Epitopes; D011498:Protein Precursors; D015800:Protozoan Proteins