Membrane contact sites between apicoplast and ER in Toxoplasma gondii revealed by electron tomography.
Toxoplasma gondii is an obligate intracellular parasite from the phylum Apicomplexa. A hallmark of these protozoans is the presence of a unique apical complex of organelles that includes the apicoplast, a plastid acquired by secondary endosymbiosis. The apicoplast is indispensible for parasite viability. It harbours a fatty acid biosynthesis type II (FAS II) pathway and plays a key role in the parasite lipid metabolism. Possibly, the apicoplast provides components for the establishment and the maturation of the parasitophorous vacuole, ensuring the successful infection of the host cell. This implies the presence of a transport mechanism for fast and accurate allocation of lipids between the apicoplast and other membrane-bound compartments in the parasite cell. Using a combination of high-pressure freezing, freeze-substitution and electron tomography, we analysed the ultrastructural organization of the apicoplast of T. gondii in relation with the endoplasmic reticulum (ER). This allowed us to clearly show the presence of four continuous membranes surrounding the apicoplast. We present, for the first time, the existence of membrane contact sites between the apicoplast outermost membrane and the ER. We describe the morphological characteristics of these structures and discuss their potential significance for the subcellular distribution of lipids in the parasite.
Tomova
Cveta
C
Electron Microscopy and Structural Analysis, Department of Biology, Faculty of Sciences, Utrecht University, 3584 CH Utrecht, The Netherlands. c.tomova@nki.nl
Humbel
Bruno M
BM
Geerts
Willie J C
WJ
Entzeroth
Rolf
R
Holthuis
Joost C M
JC
Verkleij
Arie J
AJ
D000818:Animals; D001692:Biological Transport; D002522:Chlorocebus aethiops; D016616:Cryoultramicrotomy; D055032:Electron Microscope Tomography; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000469:parasitology / Q000648:ultrastructure*; D054889:Fatty Acid Synthase, Type II / Q000096:biosynthesis*; D005227:Fatty Acids / Q000096:biosynthesis; D006790:Host-Parasite Interactions; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure*; D050356:Lipid Metabolism; D008954:Models, Biological; D015388:Organelles / Q000378:metabolism / Q000648:ultrastructure*; D013559:Symbiosis / Q000502:physiology; D014122:Toxoplasma / Q000201:enzymology / Q000378:metabolism / Q000648:ultrastructure*; D014617:Vacuoles / Q000378:metabolism / Q000469:parasitology / Q000648:ultrastructure; D014709:Vero Cells
D005227:Fatty Acids; D054889:Fatty Acid Synthase, Type II