title: Biosynthesis of the Methylthioxylose Capping Motif of Lipoarabinomannan in Mycobacterium tuberculosis.
abstract: Lipoarabinomannan (LAM) is a lipoglycan found in abundant quantities in the cell envelope of all mycobacteria. The nonreducing arabinan termini of LAM display species-specific structural microheterogeneity that impacts the biological activity of the entire molecule. Mycobacterium tuberculosis, for instance, produces mannoside caps made of one to three α-(1 → 2)-Manp-linked residues that may be further substituted with an α-(1 → 4)-linked methylthio-d-xylose (MTX) residue. While the biological functions and catalytic steps leading to the formation of the mannoside caps of M. tuberculosis LAM have been well established, the biosynthetic origin and biological relevance of the MTX motif remain elusive. We here report on the discovery of a five-gene cluster dedicated to the biosynthesis of the MTX capping motif of M. tuberculosis LAM, and on the functional characterization of two glycosyltransferases, MtxS and MtxT, responsible, respectively, for the production of decaprenyl-phospho-MTX (DP-MTX) and the transfer of MTX from DP-MTX to the mannoside caps of LAM. Collectively, our NMR spectroscopic and mass spectrometric analyses of mtxS and mtxT overexpressors and knockout mutants support a biosynthetic model wherein the conversion of 5'-methylthioadenosine, which is a ubiquitous byproduct of spermidine biosynthesis, into 5'-methylthioribose-1-phosphate precedes the formation of a 5'-methylthioribose nucleotide sugar, followed by the epimerization at C-3 of the ribose residue, and the transfer of MTX from the nucleotide sugar to decaprenyl-phosphate yielding the substrate for transfer onto LAM. The conservation of the MTX biosynthetic genes in a number of Actinomycetes suggests that this discrete glycosyl substituent may be more widespread in prokaryotes than originally thought.
authors.affiliation: Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University , Fort Collins, Colorado 80523-1682, United States.
authors.forename: Shiva Kumar
authors.initials: SK
authors.lastname: Angala
authors.affiliation: Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University , Fort Collins, Colorado 80523-1682, United States.
authors.forename: Michael R
authors.initials: MR
authors.lastname: McNeil
authors.affiliation: Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University , Fort Collins, Colorado 80523-1682, United States.
authors.forename: Libin
authors.initials: L
authors.lastname: Shi
authors.affiliation: Alberta Glycomics Centre and Department of Chemistry, The University of Alberta , Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Maju
authors.initials: M
authors.lastname: Joe
authors.affiliation: Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University , Fort Collins, Colorado 80523-1682, United States.
authors.forename: Ha
authors.initials: H
authors.lastname: Pham
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale , Université de Toulouse, CNRS, UPS, 205 route de Narbonne, F-31077 Toulouse, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Zuberogoitia
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale , Université de Toulouse, CNRS, UPS, 205 route de Narbonne, F-31077 Toulouse, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Nigou
authors.affiliation: Central Instrumentation Facility, Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523-1872, United States.
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Boot
authors.affiliation: Alberta Glycomics Centre and Department of Chemistry, The University of Alberta , Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Todd L
authors.initials: TL
authors.lastname: Lowary
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale , Université de Toulouse, CNRS, UPS, 205 route de Narbonne, F-31077 Toulouse, France.
authors.forename: Martine
authors.initials: M
authors.lastname: Gilleron
authors.affiliation: Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University , Fort Collins, Colorado 80523-1682, United States.
authors.forename: Mary
authors.identifier: 0000-0002-9212-0258
authors.initials: M
authors.lastname: Jackson
mesh_terms: D002853:Chromatography, Liquid; D008070:Lipopolysaccharides / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D009169:Mycobacterium tuberculosis / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D014994:Xylose / Q000378:metabolism*
chemical_list: D008070:Lipopolysaccharides; C050016:lipoarabinomannan; D014994:Xylose