title: Metabolic Network for the Biosynthesis of Intra- and Extracellular α-Glucans Required for Virulence of Mycobacterium tuberculosis.
abstract: Mycobacterium tuberculosis synthesizes intra- and extracellular α-glucans that were believed to originate from separate pathways. The extracellular glucose polymer is the main constituent of the mycobacterial capsule that is thought to be involved in immune evasion and virulence. However, the role of the α-glucan capsule in pathogenesis has remained enigmatic due to an incomplete understanding of α-glucan biosynthetic pathways preventing the generation of capsule-deficient mutants. Three separate and potentially redundant pathways had been implicated in α-glucan biosynthesis in mycobacteria: the GlgC-GlgA, the Rv3032 and the TreS-Pep2-GlgE pathways. We now show that α-glucan in mycobacteria is exclusively assembled intracellularly utilizing the building block α-maltose-1-phosphate as the substrate for the maltosyltransferase GlgE, with subsequent branching of the polymer by the branching enzyme GlgB. Some α-glucan is exported to form the α-glucan capsule. There is an unexpected convergence of the TreS-Pep2 and GlgC-GlgA pathways that both generate α-maltose-1-phosphate. While the TreS-Pep2 route from trehalose was already known, we have now established that GlgA forms this phosphosugar from ADP-glucose and glucose 1-phosphate 1000-fold more efficiently than its hitherto described glycogen synthase activity. The two routes are connected by the common precursor ADP-glucose, allowing compensatory flux from one route to the other. Having elucidated this unexpected configuration of the metabolic pathways underlying α-glucan biosynthesis in mycobacteria, an M. tuberculosis double mutant devoid of α-glucan could be constructed, showing a direct link between the GlgE pathway, α-glucan biosynthesis and virulence in a mouse infection model.
authors: Institute for Medical Microbiology and Hospital Hygiene, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
authors: Hendrik
authors: H
authors: Koliwer-Brandl
authors: Department of Biological Chemistry, John Innes Centre, Norwich, United Kingdom.
authors: Karl
authors: K
authors: Syson
authors: Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
authors: Robert
authors: R
authors: van de Weerd
authors: Department of Molecular Microbiology, John Innes Centre, Norwich, United Kingdom.
authors: Govind
authors: G
authors: Chandra
authors: Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
authors: Ben
authors: B
authors: Appelmelk
authors: Institute for Medical Microbiology and Hospital Hygiene, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
authors: Marina
authors: M
authors: Alber
authors: Department of Computer Science and Engineering, Texas A&M University, College Station, Texas, United States of America.
authors: Thomas R
authors: TR
authors: Ioerger
authors: Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, United States of America.
authors: William R
authors: WR
authors: Jacobs
authors: Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam, The Netherlands.
authors: Jeroen
authors: J
authors: Geurtsen
authors: Department of Biological Chemistry, John Innes Centre, Norwich, United Kingdom.
authors: Stephen
authors: S
authors: Bornemann
authors: Institute for Medical Microbiology and Hospital Hygiene, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.|Institute for Pharmaceutical Biology and Biotechnology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
authors: Rainer
authors: 0000-0002-3378-2067
authors: R
authors: Kalscheuer
mesh_terms: D000818:Animals; D016667:Bacterial Capsules / Q000378:metabolism*; D001426:Bacterial Proteins / Q000096:biosynthesis; D002855:Chromatography, Thin Layer; D004195:Disease Models, Animal; D005260:Female; D005936:Glucans / Q000096:biosynthesis*; D007150:Immunohistochemistry; D053858:Metabolic Networks and Pathways / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009169:Mycobacterium tuberculosis / Q000378:metabolism / Q000472:pathogenicity*; D016133:Polymerase Chain Reaction; D014376:Tuberculosis / Q000378:metabolism*; D014774:Virulence / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D005936:Glucans