The Cell‐Wall Core of
            <i>Mycobacterium</i>
            : Structure, Biogenesis and Genetics

Baulard, Alain R.; Besra, Gurdyal S.; Brennan, Patrick J.

doi:10.1002/9781444311433.ch13

Cited by 13 publications

(7 citation statements)

References 39 publications

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“…The ligation of AG to PG involves the transphosphorylation of the terminal GlcNAc-1-P of the LU of the AG polymer from its polyprenyl-P carrier to the 6-position of the N-glycolylmuramic acid residues of PG (25). The reaction closely resembles the ligation of teichoic acid and other anionic polymers to PG in a wide range of Gram-positive bacteria and is a prime candidate for antibiotic intervention in the case of Staphylococcus and Streptococcus infections (21).…”

Section: Figmentioning

confidence: 99%

Polymerization of Mycobacterial Arabinogalactan and Ligation to Peptidoglycan

Yagi¹,

Mahapatra

Mikušová³

et al. 2003

Journal of Biological Chemistry

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The cell wall of Mycobacterium spp. consists predominately of arabinogalactan chains linked at the reducing ends to peptidoglycan via a P-GlcNAc-(␣1-3)-Rha linkage unit (LU) and esterified to a variety of mycolic acids at the nonreducing ends. Several aspects of the biosynthesis of this complex have been defined, including the initial formation of the LU on a polyprenyl phosphate (Pol-P) molecule followed by the sequential addition of galactofuranosyl (Galf) units to generate Pol-P-P-LU-(Galf) 1,2,3, etc. and Pol-P-P-LU-galactan, catalyzed by a bifunctional galactosyltransferase (Rv3808c) capable of adding alternating 5-and 6-linked Galf units. By applying cell-free extracts of Mycobacterium smegmatis, containing cell wall and membrane fragments, and differential labeling with UDP-[ 14 C]Galp and recombinant UDP-Galp mutase as the source of [ C]Galf for galactan biosynthesis and 5-P-[14 C]ribosyl-P-P as a donor of [ 14 C]Araf for arabinan synthesis, we now demonstrate sequential synthesis of the simpler Pol-P-P-LU-(Galf) n glycolipid intermediates followed by the Pol-P-P-LU-arabinogalactan and, finally, ligation of the P-LU-arabinogalactan to peptidoglycan. This first time demonstration of in vitro ligation of newly synthesized P-LUarabinogalactan to newly synthesized peptidoglycan is a necessary forerunner to defining the genetics and enzymology of cell wall polymer-peptidoglycan ligation in Mycobacterium spp. and examining this step as a target for new antibacterial drugs.The cell envelope of Mycobacterium tuberculosis is composed of a conventional plasma membrane and a cell wall proper unique to some genera within the Actinomycetales order, consisting of a core of arabinogalactan (AG), 1 peptidoglycan (PG), and mycolic acids interspersed with a variety of free lipids, lipoglycans, and proteins (1); there is also evidence for polysaccharides on the outer face of the cell wall (2). The mycolic acids are attached to the nonreducing ends of the arabinogalactan, whereas the reducing ends are covalently attached to the crosslinked peptidoglycan via phosphoryl-N-acetylglucosaminosylrhamnosyl linkage units (P-GlcNAc-Rha). This massive structure, the mycolate-arabinogalactan-peptidoglycan-complex (MAPc), is the basis of many of the physiological and pathogenic features of M. tuberculosis and the site of susceptibility and resistance to many of the anti-tuberculosis drugs (3). Biosynthesis of this complex commences with attachment of the residues of the linkage unit, GlcNAc-1-P and Rha, donated by UDP-GlcNAc and dTDP-Rha, respectively, to a polyprenyl phosphate (Pol-P) carrier lipid (4). Formation of the linkage unit is followed by the sequential addition of galactofuranosyl (Galf) units donated by UDP-Galf, to provide simple Pol-P-Plinked AG intermediates (4). The bulk, if not all, of galactan biosynthesis is catalyzed by a membrane-associated bifunctional galactosyltransferase capable of adding the alternating 5-and 6-linked Galf units (5, 6).The demonstration that the direct donor of the arabinofuranosyl (Araf) unit...

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Section: Figmentioning

confidence: 99%

Polymerization of Mycobacterial Arabinogalactan and Ligation to Peptidoglycan

Yagi¹,

Mahapatra

Mikušová³

et al. 2003

Journal of Biological Chemistry

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“…1). The insoluble cell wall core is an insoluble matrix of crosslinked peptidoglycans linked to arabinogalactans, esterified at the distal ends to mycolic acids [3]. Although these major cell wall constituents are relatively well described, their three-dimensional distribution remains poorly understood and somewhat controversial [10,16].…”

Section: Introductionmentioning

confidence: 99%

Organization of the mycobacterial cell wall: a nanoscale view

Alsteens

Verbelen

Dague

et al. 2007

Pflugers Arch - Eur J Physiol

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The biosynthesis of the Mycobacterium tuberculosis cell wall is targeted by some of the most powerful antituberculous drugs. To date, the molecular mechanisms by which these antibiotics affect the cell wall characteristics are not well understood. Here, we used atomic force microscopy -in three different modes -to probe the nanoscale surface properties of live mycobacteria and their modifications upon incubation with four antimycobacterial drugs: isoniazid, ethionamide, ethambutol, and streptomycine. Topographic imaging, combined with quantitative surface roughness analysis, demonstrated that all drugs induce a substantial increase of surface roughness to an extent that correlates with the localization of the target (i.e., synthesis of mycolic acids, arabinogalactans, or proteins). Chemical force microscopy with hydrophobic tips revealed that the structural alterations induced by isoniazid and ethambutol were correlated with a dramatic decrease of cell surface hydrophobicity, reflecting the removal of the outermost mycolic acid layer. Consistent with this finding, tapping mode imaging, combined with immunogold labeling, showed that the two drugs lead to the massive exposure of hydrophilic lipoarabinomannans at the surface. Taken together, these structural, chemical, and immunological data provide novel insight into the action mode of antimycobacterial drugs, as well as into the spatial organization of the mycobacterial cell wall.

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“…Although this infection can be treated effectively with multidrug therapy, incomplete treatment has led to the development of drug-resistant strains leading to the urgent need for specific targets for new anti-microbial agents. Since the cell wall is an attractive target for antibiotic development, considerable efforts have been focused on discovering the metabolic steps that are essential for biosynthesis of mycobacterial cell-wall components (Baulard et al, 1999 ;Besra et al, 1997 ;Lee et al, 1996 ;Mikusova et al, 1996). antibiotics.…”

Section: Introductionmentioning

confidence: 99%