title: A novel family of Toxoplasma IMC proteins displays a hierarchical organization and functions in coordinating parasite division.
abstract: Apicomplexans employ a peripheral membrane system called the inner membrane complex (IMC) for critical processes such as host cell invasion and daughter cell formation. We have identified a family of proteins that define novel sub-compartments of the Toxoplasma gondii IMC. These IMC Sub-compartment Proteins, ISP1, 2 and 3, are conserved throughout the Apicomplexa, but do not appear to be present outside the phylum. ISP1 localizes to the apical cap portion of the IMC, while ISP2 localizes to a central IMC region and ISP3 localizes to a central plus basal region of the complex. Targeting of all three ISPs is dependent upon N-terminal residues predicted for coordinated myristoylation and palmitoylation. Surprisingly, we show that disruption of ISP1 results in a dramatic relocalization of ISP2 and ISP3 to the apical cap. Although the N-terminal region of ISP1 is necessary and sufficient for apical cap targeting, exclusion of other family members requires the remaining C-terminal region of the protein. This gate-keeping function of ISP1 reveals an unprecedented mechanism of interactive and hierarchical targeting of proteins to establish these unique sub-compartments in the Toxoplasma IMC. Finally, we show that loss of ISP2 results in severe defects in daughter cell formation during endodyogeny, indicating a role for the ISP proteins in coordinating this unique process of Toxoplasma replication.
authors.affiliation: Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, Los Angeles, California, United States of America.
authors.forename: Josh R
authors.initials: JR
authors.lastname: Beck
authors.forename: Imilce A
authors.initials: IA
authors.lastname: Rodriguez-Fernandez
authors.forename: Jessica Cruz
authors.initials: JC
authors.lastname: de Leon
authors.forename: My-Hang
authors.initials: MH
authors.lastname: Huynh
authors.forename: Vern B
authors.initials: VB
authors.lastname: Carruthers
authors.forename: Naomi S
authors.initials: NS
authors.lastname: Morrissette
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Bradley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002455:Cell Division; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000469:parasitology*; D052816:Foreskin / Q000166:cytology / Q000469:parasitology; D006801:Humans; D007114:Immunization; D007074:Immunoglobulin G / Q000276:immunology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014122:Toxoplasma / Q000502:physiology*; D014123:Toxoplasmosis / Q000235:genetics / Q000378:metabolism* / Q000469:parasitology
chemical_list: D007074:Immunoglobulin G; D008565:Membrane Proteins; D015800:Protozoan Proteins; D012333:RNA, Messenger