title: Role of an ancestral d-bifunctional protein containing two sterol-carrier protein-2 domains in lipid uptake and trafficking in Toxoplasma.
abstract: The inability to synthesize cholesterol is universal among protozoa. The intracellular pathogen Toxoplasma depends on host lipoprotein-derived cholesterol to replicate in mammalian cells. Mechanisms of cholesterol trafficking in this parasite must be important for delivery to proper organelles. We characterized a unique d-bifunctional protein variant expressed by Toxoplasma consisting of one N-terminal d-3-hydroxyacyl-CoA dehydrogenase domain fused to two tandem sterol carrier protein-2 (SCP-2) domains. This multidomain protein undergoes multiple cleavage steps to release free SCP-2. The most C-terminal SCP-2 carries a PTS1 that directs the protein to vesicles before processing. Abrogation of this signal results in SCP-2 accumulation in the cytoplasm. Cholesterol specifically binds to parasite SCP-2 but with 10-fold lower affinity than phosphatidylcholine. In mammalian cells and Toxoplasma, the two parasite SCP-2 domains promote the circulation of various lipids between organelles and to the surface. Compared with wild-type parasites, TgHAD-2SCP-2-transfected parasites replicate faster and show enhanced uptake of cholesterol and oleate, which are incorporated into neutral lipids that accumulate at the basal end of Toxoplasma. This work provides the first evidence that the lipid transfer capability of an ancestral eukaryotic SCP-2 domain can influence the lipid metabolism of an intracellular pathogen to promote its multiplication in mammalian cells.
authors.affiliation: Department of Molecular Microbiology and Immunology, Johns Hopkins University School of Public Health, Baltimore, MD 21205, USA.
authors.forename: Bao
authors.initials: B
authors.lastname: Lige
authors.forename: Bamini
authors.initials: B
authors.lastname: Jayabalasingham
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Marc
authors.initials: M
authors.lastname: Pypaert
authors.forename: Isabelle
authors.initials: I
authors.lastname: Coppens
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000502:physiology*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D006801:Humans; D006836:Hydro-Lyases / Q000235:genetics / Q000378:metabolism; D050356:Lipid Metabolism; D008563:Membrane Lipids / Q000378:metabolism; D008969:Molecular Sequence Data; D064029:Peroxisomal Multifunctional Protein-2; D020675:Peroxisomes / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013261:Sterols / Q000378:metabolism*; D014122:Toxoplasma / Q000166:cytology / Q000378:metabolism*; D015211:Zellweger Syndrome / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; D013261:Sterols; C072087:sterol carrier proteins; D002784:Cholesterol; D015067:17-Hydroxysteroid Dehydrogenases; D006836:Hydro-Lyases; D064029:Peroxisomal Multifunctional Protein-2; C104587:HSD17B4 protein, human