THE TRYPANOSOME VARIANT SURFACE GLYCOPROTEIN
Principal Investigator: PAUL ENGLUND
Affiliation: Johns Hopkins University
Abstract: African trypanosomes are parasitic protozoa which are responsible for human and animal diseases. They inhabit their host's bloodstream, and they evade immune defenses by antigenic variation. Antigenic variation is mediated by the variant surface glycoprotein (VSG), which forms a coat covering the entire cell. During antigenic variation, the parasite synthesizes a new VSG, with a different amino acid sequence, exchanging its old coat for a new one. Trypanosomes have the genetic potential to synthesize hundreds of different VSG molecules, and therefore they can maintain a chronic infection. This research involves the biochemistry of VSG, focusing particularly on the myristate-containing glycosyl phosphatidylinositol (GPI) which anchors it to the plasma membrane. The GPI is synthesized as a precursor, glycolipid A, which is linked to the C-terminus of the newly-made VSG. Previous studies, using a cell free system, have revealed the pathway for biosynthesis of glycolipid A and the remodeling mechanism by which myristate is incorporated into this structure. Proposed studies consist of further analysis of the mechanism by which myristate is incorporated into the GPI and also the mechanism for incorporation of its phosphoethanolamine. Other studies will focus on trypanosome myristate metabolism, with special emphasis on mechanisms of myristate uptake and intracellular transport to the site of GPI biosynthesis. There will be additional investigations of myristate analogs which are selectively toxic to African trypanosomes, possible because they interfere with VSG biosynthesis or function. Earlier studies on GPI biosynthesis and myristoylation have involved crude membrane fractions; however, a more comprehensive understanding of these processes will require enzyme purification. Purification will also allow cloning of the genes regulating GPI biosynthesis and myristoylation, and new genetic techniques will allow specific mutation of these genes in trypanosomes. This genetic analysis will allow biological studies of the effect of defective GPI biosynthesis or myristoylation. The same genetic approach will be applied to GPI-specific phospholipase C (GPI-PLC), an enzyme which cleaves the VSG anchor.
Funding Period: 1984-05-01 - 1997-04-30
more information: NIH RePORT
- Fatty acid synthesis by elongases in trypanosomesSoo Hee Lee
Department of Biological Chemistry, Johns Hopkins Medical School, Baltimore, MD 21205, USA
Cell 126:691-9. 2006..In blood, ELO3 downregulation favors myristate synthesis, whereas low concentrations of exogenous fatty acids in cultured parasites cause upregulation of the entire pathway, allowing the parasite to adapt to different environments...
- RNAi libraries and kinetoplast DNAP T Englund
Department of Biological Chemistry, Johns Hopkins Medical School, 725 N Wolfe St, Baltimore, MD 21205, USA
Biochem Soc Trans 33:1409-12. 2005..To identify genes for more kDNA replication proteins, we are using an RNA interference library, which is the first forward genetic approach used for these parasites...
- Mitochondrial fatty acid synthesis in Trypanosoma bruceiJennifer L Stephens
Department of Biological Chemistry, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA
J Biol Chem 282:4427-36. 2007..Trypanosomes employ two FAS systems: the unconventional ELO pathway that synthesizes bulk fatty acids and a mitochondrial pathway that synthesizes specialized fatty acids that are likely utilized intramitochondrially...
- Mitochondrial fatty acid synthesis is required for normal mitochondrial morphology and function in Trypanosoma bruceiJennifer L Guler
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, USA
Mol Microbiol 67:1125-42. 2008..Thus, we conclude that the mitochondrial synthase produces fatty acids needed for maintaining local phospholipid levels that are required for activity of respiratory complexes and preservation of mitochondrial morphology and function...
- The 3-hydroxyacyl-ACP dehydratase of mitochondrial fatty acid synthesis in Trypanosoma bruceiKaija J Autio
Department of Biochemistry and Biocenter Oulu, University of Oulu, Oulu, Finland
FEBS Lett 582:729-33. 2008..TbHTD2 can rescue the respiratory deficient phenotype of the yeast knock-out strain and restore the lipoic acid content, is localized in the mitochondrion and exhibits hydratase 2 activity...
- Silencing of genes required for glycosylphosphatidylinositol anchor biosynthesis in Burkitt lymphomaRong Hu
Division of Hematology, Johns Hopkins University School of Medicine, Baltimore, MD 21205 2196, USA
Exp Hematol 37:423-434.e2. 2009..To investigate the mechanism of glycosylphosphatidylinositol (GPI) anchor deficiency in Burkitt lymphoma cell lines...