Newly found 2-N-acetyl-2,6-dideoxy- -glucopyranose containing methyl glucose polysaccharides in M.bovis BCG: Revised structure of the mycobacterial methyl glucose lipopolysaccharides

Abstract

The specific mycobacterial methyl polysaccharides 3- O -methyl mannose polysaccharide (MMP) and the 6- O -methyl glucose lipopolysaccharides (MGLPs) were shown to modulate the fatty acid biosynthesis by the mycobacterial fatty acid synthetase I (FAS I). This activity is attributed to their fatty acid complexing properties allowing the release of the neo synthesized fatty acyl chain from the enzyme and probably their transport in the cell. To elucidate, at a molecular level, the mechanism of this unusual kind of polysaccharide-lipid biological interaction, we first analyzed, by mass spectrometry and proton nuclear magnetic resonance (1H NMR) spectroscopy, the structure of the polysaccharidic backbone (MGPs) of the MGLPs from Mycobacterium bovis BCG. This work reveals that this strain produces a new kind of MGP containing an unusual monosaccharide never described in the mycobacterial genus: a 2- N -acetyl-2,6-dideoxy-beta-glucopyranosyl. In addition,1H NMR data afforded evidence for the revision of three glycosidic linkages described previously. These modifications affect mainly the reducing end tetrasaccharide and have great consequences on the previously proposed molecular model of the MGP.

Genetic Basis for the Biosynthesis of Methylglucose Lipopolysaccharides in Mycobacterium tuberculosis

“…1. MMP have been found in multiple nonpathogenic fast growing species of mycobacteria (16) and in Streptomyces griseus (17), whereas MGLP have been isolated from several Nocardia species as well as M. phlei, M. smegmatis, Mycobacterium bovis BCG, M. tuberculosis, M. leprae,[13][14][15]18,19).Ballou and co-workers (2, 16, 20, 21) isolated precursors of MMP and characterized an ␣-(134)-mannosyltransferase and a 3-O-methyltransferase from cell-free extracts of M. smegmatis. These studies led to a biosynthetic model in which MMP is elongated by a linear alternating process of mannosylation followed by O-methylation, in which GDP-Man serves as the sugar donor for the mannosyltransferase and S-adenosylmethionine serves as the source of methyl groups.…”

“…1. MMP have been found in multiple nonpathogenic fast growing species of mycobacteria (16) and in Streptomyces griseus (17), whereas MGLP have been isolated from several Nocardia species as well as M. phlei, M. smegmatis, Mycobacterium bovis BCG, M. tuberculosis, M. leprae,[13][14][15]18,19).…”

To be or not to be a compatible solute: Bioversatility of mannosylglycerate and glucosylglycerate

“…Free GG had been detected in trace amounts in Mycobacterium smegmatis and was considered to be the precursor for a GG-containing polysaccharide almost exclusively found in mycobacteria, designated methylglucose lipopolysaccharide [28,50]. This unusual polysaccharide contains about 16-20 hexoses some of which are methylated and have variable levels of acetate, propionate, isobutyrate and octanoate and succinic acid as lateral groups, while GG is located at the reducing end of the molecule [32,51].…”

“…The biosynthesis of GG in mycobacteria as precursor for the MGLP The identification of GG in the mycobacterial MGLP, as well as detection of homologues (40% amino acid identity) to the mpgS from R. xylanophilus in mycobacterial genomes, led to the study of the genes from two species from which the MGLPs have been studied, the fast-growing M. smegmatis and the slow-growing M. bovis BCG [18,28,50]. The corresponding recombinant Fig.…”

Mechanism of Dephosphorylation of Glucosyl-3-phosphoglycerate by a Histidine Phosphatase

“…The biosynthesis of MGLPs requires the concerted action of many enzymes (Fig. 1A) (7)(8)(9)(10). These include enzymes necessary for the transfer of glucosyl, methyl, and acetyl groups, as well as accessory enzymes like glucoside hydrolases and phosphatases.…”