title: EtMIC4: a microneme protein from Eimeria tenella that contains tandem arrays of epidermal growth factor-like repeats and thrombospondin type-I repeats.
abstract: Micronemes are specialised secretory organelles that release their proteins by a stimulus-coupled exocytosis that occurs when apicomplexan parasites make contact with target host cells. These proteins play crucial roles in motility and invasion, most likely by mediating adhesion between parasite and host cell surfaces and facilitating the transmission of dynamic forces generated by the parasite actinomyosin cytoskeleton. Members of the TRAP family of microneme proteins are characterised by having extracellular domains containing one or more types of cysteine-rich, adhesive modules, highly-conserved transmembrane regions and cytosolic tails that contain one or more tyrosines, stretches of acidic residues and a single tryptophan. In this paper, we describe a novel member of the TRAP family, EtMIC4, a 218 kDa microneme protein from Eimeria tenella. EtMIC4 contains 31 epidermal growth factor (EGF) modules, 12 thrombospondin type-1 (TSP-1) modules and a highly acidic, proline and glycine-rich region in its extracellular region, plus the conserved transmembrane and cytosolic tail. Like EtMIC1, another TRAP family member from E. tenella, EtMIC4 is expressed in sporozoites and all the merozoite stages of the parasite, suggesting that this parasite has a strong requirement for TSP-1 modules. Unlike the other microneme proteins so far studied in E. tenella, EtMIC4 appears to be found constitutively on the sporozoite surface as well as within the micronemes.
authors.affiliation: Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berkshire, RG20 7NN, UK. fiona.tomley@bbsrc.ac.uk
authors.forename: F M
authors.initials: FM
authors.lastname: Tomley
authors.forename: K J
authors.initials: KJ
authors.lastname: Billington
authors.forename: J M
authors.initials: JM
authors.lastname: Bumstead
authors.forename: J D
authors.initials: JD
authors.lastname: Clark
authors.forename: P
authors.initials: P
authors.lastname: Monaghan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D015815:Cell Adhesion Molecules / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D020285:Cryoelectron Microscopy; D016786:Eimeria tenella / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000737:chemistry*; D015870:Gene Expression; D006790:Host-Parasite Interactions; D008969:Molecular Sequence Data; D008970:Molecular Weight; D015388:Organelles / Q000737:chemistry; D015800:Protozoan Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment; D020080:Tandem Repeat Sequences; D019700:Thrombospondin 1 / Q000737:chemistry*
chemical_list: D015815:Cell Adhesion Molecules; C428323:MIC4 protein, Toxoplasma gondii; D015800:Protozoan Proteins; D019700:Thrombospondin 1; D004815:Epidermal Growth Factor