Structural Elucidation of Novel Methylglucose‐Containing Polysaccharides from Mycobacterium xenopi

Abstract

The structures of methylglucose-containing polysaccharides (MeGlc PS) from MycobacteriLim xenopi were investigated using high-pH anion-exchange chromatography and liquid secondary-ion mass spectrometry. We report the structure of two novel MeGlc PS, referred to as A and B. MeGlc PS A is composed of 16 D-glUCopyranoSe residues, 11 of which are methylated, and MeGlc PS B contains 15 D-glucopyranose residues, 10 of which are methylated. The main structural feature of both MeGlc PS A and B, compared to the previously described structures, is the absence of the tetrasaccharide non-reducing Pathogenic mycobacteria, such as Mycobacteriuin tuherculosis and Mycobacteriwn leprae, the causative agents of tuberculosis and leprosy, respectively, are able to survive in the hostile host macrophage cell. This property is partly related to the presence of a thick lipid-rich cell wall surrounding the mycobacteria. This cell wall contains characteristic a-ramified p-hydroxylated long-chain fatty acids called mycolic acids, which are covalently linked to the arabinogalactan-peptidoglycan complex and to trehalose. These fatty acids provide a monolayer of unusually high order and low fluidity and thus could represent a hydrophobic barrier to the diffusion of hydrophilic molecules and, in particular, for polar antibiotics (Jarlier and Nikai'do, 1994). lsonicotinic hydrazide (isoniazide), probably the most widely used antituberculous drug, is known to inhibit mycolic acid biosynthesis in a mycobacterial cell-free extract o f Mycobacterium aurum (Quemard et al., 1991) suggesting the key role of these fatty acids in the viability of the mycobacteria inside the host macrophage. Unfortunately, the use of isoniazide and other antibiotics is not always effective due to the emergence of multidrug-resistant M. tuberculosis strains (Iseman, 1994). This new aspect of tuberculosis epidemiology represents a major public health problem and has caused a renewal of interest in cell wall component biosynthesis.Correspondence to M. Rivikre, Laboratoire de Pharmacologie et de Toxicologie Fondamentales du Centre National de la Recherche Scientifique, 11 8 Route de Narbonne, F-31062 Toulouse Cedex, FranceAbbreviarions. PS, polysaccharide(s); MeGlc PS,,,,,,, methylglucose polysaccharide composed of M glucose residues n of which are mono-0-methylated; LPS, lipopolysaccharide(s) ; AG-MeClc PS, a-amylasedigested and glucose-amylase-digested methylglucose polysaccharides ; polyMe PS, polymethyl polysaccharides; HPAEC, high-pH anion-exchange chromatography; LSIMS, liquid secondary-ion mass spectrometry ; LSIMS/MS, tandem liquid secondary-ion mass spectrometry; FAB/ MS, fast-atom-bombardment mass spectrometry.

Microbial Type I Fatty Acid Synthases (FAS): Major Players in a Network of Cellular FAS Systems

“…Distinct mycobacterial polysaccharides were found to increase both the production of shorter-chain fatty acids and the overall rate of fatty acid synthesis (9,13,106,165,182). The promoting effect of these polysaccharides was attributed in particular to the facilitated release of long-chain acyl-CoA from the enzyme (13).…”

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).…”

Mycobacterium tuberculosis Rv2419c, the missing glucosyl-3-phosphoglycerate phosphatase for the second step in methylglucose lipopolysaccharide biosynthesis

“…These polysaccharides form stable 1∶1 complexes with fatty acids and modulate the activity of fatty acid synthase I in vitro 6. While MGLP has been found in both slow- and rapid-growing mycobacteria and also in Nocardia otitidiscaviarum , MMP has been detected in rapid-growing mycobacteria and in Streptomyces griseus 478910.…”