title: Assembly of α-Glucan by GlgE and GlgB in Mycobacteria and Streptomycetes.
abstract: Actinomycetes, such as mycobacteria and streptomycetes, synthesize α-glucan with α-1,4 linkages and α-1,6 branching to help evade immune responses and to store carbon. α-Glucan is thought to resemble glycogen except for having shorter constituent linear chains. However, the fine structure of α-glucan and how it can be defined by the maltosyl transferase GlgE and branching enzyme GlgB were not known. Using a combination of enzymolysis and mass spectrometry, we compared the properties of α-glucan isolated from actinomycetes with polymer synthesized in vitro by GlgE and GlgB. We now propose the following assembly mechanism. Polymer synthesis starts with GlgE and its donor substrate, α-maltose 1-phosphate, yielding a linear oligomer with a degree of polymerization (∼16) sufficient for GlgB to introduce a branch. Branching involves strictly intrachain transfer to generate a C chain (the only constituent chain to retain its reducing end), which now bears an A chain (a nonreducing end terminal branch that does not itself bear a branch). GlgE preferentially extends A chains allowing GlgB to act iteratively to generate new A chains emanating from B chains (nonterminal branches that themselves bear a branch). Although extension and branching occur primarily with A chains, the other chain types are sometimes extended and branched such that some B chains (and possibly C chains) bear more than one branch. This occurs less frequently in α-glucans than in classical glycogens. The very similar properties of cytosolic and capsular α-glucans from Mycobacterium tuberculosis imply GlgE and GlgB are sufficient to synthesize them both.
authors.affiliation: Biological Chemistry Department, John Innes Centre , Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Abdul M
authors.initials: AM
authors.lastname: Rashid
authors.affiliation: Biological Chemistry Department, John Innes Centre , Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Sibyl F D
authors.initials: SF
authors.lastname: Batey
authors.affiliation: Biological Chemistry Department, John Innes Centre , Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Karl
authors.initials: K
authors.lastname: Syson
authors.affiliation: Institute for Medical Microbiology and Hospital Hygiene, and Institute for Pharmaceutical Biology and Biotechnology, Heinrich-Heine-University Düsseldorf , Universitätsstrasse 1, 40225 Düsseldorf, Germany.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Koliwer-Brandl
authors.affiliation: Biological Chemistry Department, John Innes Centre , Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Farzana
authors.initials: F
authors.lastname: Miah
authors.affiliation: Cell and Developmental Biology Department, John Innes Centre , Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: J Elaine
authors.initials: JE
authors.lastname: Barclay
authors.affiliation: Cell and Developmental Biology Department, John Innes Centre , Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Kim C
authors.initials: KC
authors.lastname: Findlay
authors.affiliation: School of Pharmacy, University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
authors.forename: Karol P
authors.initials: KP
authors.lastname: Nartowski
authors.affiliation: School of Pharmacy, University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
authors.forename: Yaroslav Z
authors.initials: YZ
authors.lastname: Khimyak
authors.affiliation: Institute for Medical Microbiology and Hospital Hygiene, and Institute for Pharmaceutical Biology and Biotechnology, Heinrich-Heine-University Düsseldorf , Universitätsstrasse 1, 40225 Düsseldorf, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Kalscheuer
authors.affiliation: Biological Chemistry Department, John Innes Centre , Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Stephen
authors.initials: S
authors.lastname: Bornemann
mesh_terms: D019075:Electrophoresis, Capillary; D005936:Glucans / Q000737:chemistry* / Q000378:metabolism*; D005964:Glucosyltransferases / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D009161:Mycobacterium / Q000145:classification / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013306:Streptomycetaceae / Q000378:metabolism*; D013403:Sugar Phosphates / Q000378:metabolism*
chemical_list: D005936:Glucans; D013403:Sugar Phosphates; C080751:maltose 1-phosphate; D005964:Glucosyltransferases; C436710:maltosyltransferase