title: Biosynthesis of the mycobacterial O-methylglucose lipopolysaccharide. Characterization of putative intermediates in the initiation, elongation, and termination reactions.
abstract: From the 70% ethanol extract of Mycobacterium smegmatis cells, we isolated a mixture of weakly acidic oligosaccharides composed mainly of glucose and 6-O-methylglucose. The elution pattern from a Bio-Gel P-4 column suggested that the oligosaccharides were smaller than the O-methylglucose polysaccharide (MGP) and could be biosynthetic precursors. Analysis by fast-atom-bombardment mass spectrometry revealed that the oligosaccharides fit into a pattern for polysaccharide synthesis based on an alternate glucosylation-methylation mechanism until the chain reached the composition methylglucose11glucose5glyceric acid, at which time 2 glucose units are added to give glucose2methylglucose11glucose5glyceric acid. The addition of the last 2 glucoses and methylation of one of them to give mature MGP (methylglucose1glucose3methylglucose11glucose5glyceric acid) apparently occurs rapidly because the expected intermediates were not observed. Only 4 glucose units are present at the glyceric acid end of some molecules during all stages of the elongation process, and these represent precursors of a minor MGP homolog with an extra methyl group on the beta 1----3-linked glucose unit of MGP. alpha-D-Glucopyranosyl-(1----2)-D-glyceric acid and alpha-D-glucopyranosyl-(1----6)-alpha-D-glucopyranosyl-(1----2)-D-glycer ic acid were also isolated from the extract and correspond in structure to the expected initial precursors.
mesh_terms: D002240:Carbohydrate Sequence; D008070:Lipopolysaccharides / Q000096:biosynthesis*; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D009161:Mycobacterium / Q000378:metabolism*
chemical_list: D008070:Lipopolysaccharides; D008757:Methylglucosides; D008759:Methylglycosides; C033884:6-O-methylglucose