title: Characterization of a specific arabinosyltransferase activity involved in mycobacterial arabinan biosynthesis.
abstract: Mycobacterium smegmatis strains that contain inactivated EmbA or EmbB proteins are unable to synthesize terminal Arabeta1-->2Araalpha1-->5(Arabeta1-->2Araalpha1-->3)Araalpha1-->5Araalpha1-->(Ara(6)) motif in the cell wall polysaccharide arabinogalactan. Instead, the mutants contain a linear Arabeta1-->2Araalpha1-->5Araalpha1-->5Araalpha1-->(Ara(4)) motif, suggesting that these proteins are involved in the synthesis or transfer of the disaccharide Arabeta1-->2Araalpha1--> to an internal 5-linked Ara. Therefore, we synthesized a linear Arabeta1-->2Araalpha1-->5Araalpha1-->5Araalpha1-->5Araalpha1--> with an octyl aglycon as an arabinosyl acceptor in cell-free assays. A facile assay was developed using the chemically synthesized glycan, membrane, and particulate cell wall as the enzyme source, and 5-phosphoribose diphosphate pR[(14)C]pp as the arabinose donor. The results unequivocally show that two arabinofuranosyl residues were added at the tertiary -->5Araalpha1--> of the synthetic glycan. This activity was undetectable in strains of M. smegmatis where embB or embA had been genetically disrupted. Normal activity could be restored only in the presence of both EmbA and EmbB proteins.
authors.affiliation: Mycobacteria Research Laboratories, Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, 80523, USA.
authors.forename: Shampa
authors.initials: S
authors.lastname: Khasnobis
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Shiva K
authors.initials: SK
authors.lastname: Angala
authors.forename: Anita G
authors.initials: AG
authors.lastname: Amin
authors.forename: Michael R
authors.initials: MR
authors.lastname: McNeil
authors.forename: Dean C
authors.initials: DC
authors.lastname: Crick
authors.forename: Delphi
authors.initials: D
authors.lastname: Chatterjee
mesh_terms: D002240:Carbohydrate Sequence; D008969:Molecular Sequence Data; D009161:Mycobacterium / Q000201:enzymology*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010430:Pentosyltransferases / Q000737:chemistry / Q000378:metabolism*; D011134:Polysaccharides / Q000096:biosynthesis* / Q000737:chemistry
chemical_list: D011134:Polysaccharides; C030080:araban; D010430:Pentosyltransferases; C101967:arabinosyltransferase