The 6-O-Methylglucose-containing Lipopolysaccharide of Mycobacterium phlei

The methylglucose polysaccharide (MGP) from mycobacterial species was digested with α-amylase and glucoamylase and then partially hydrolyzed with acid, and the resulting oligosaccharides were reduced with sodium borotritide. By means of gel filtration and paper chromatography, an homologous series of α-(1 → 4)-linked oligosaccharides containing only 6-O-methylglucose were isolated, the largest of which was a decasaccharide. Exhaustive digestion of MGP by α-amylase and glucoamylase released 4 sugar residues per molecule of polysaccharide, 3 glucose units, and 1 of 3-O-methylglucose. Since these four sugars were released, in part, as a tetrasaccharide by α-amylase, and since the newly exposed nonreducing terminus was 6-O-methylglucose, it follows that the tetrasaccharide was attached as a unit to the 6-O-methylglucose-containing section of the main chain of the polysaccharide. From the total glucose content of the polysaccharide (7 moles) and the fact that 6 moles were assigned to the main chain, it is concluded that the glucose-containing side chain is a single glucose unit attached to position 3 of the first 6-O-methylglucose unit in the main chain. Confirmation of the above conclusions was obtained in other experiments. MGP was oxidized by sodium periodate, the polyaldehyde was reduced with sodium borotritide, and the products obtained by acid hydrolysis were determined. These were erythritol (4 moles), glycerol (2.6 moles), 1-O-methylerythritol (8.9 moles), glucose (1 mole), 6-O-methylglucose (1 mole), and 3-O-methylglucose (1 mole). Mild acid hydrolysis of the periodate-oxidized and borohydride-reduced MGP yielded 6-O-methylglucosyl-(1 → 2) erythritol and α-glucosyl-(1 → 1)-glycerol. The data presented here and in the preceding publications allow us to propose the complete structure for the polysaccharide. A search for 6-O-methylglucose-containing lipopolysaccharides in species of Propionibacterium, Corynebacterium, and Nocardia gave negative results. Because these bacteria are thought to be among the closest phylogenetic relatives of the mycobacteria, the methylglucose lipopolysaccharide may be unique to this genus. The intact lipopolysaccharide had no effect on the growth of selected gram-negative and gram-positive bacteria.