Genetic Basis for the Biosynthesis of Methylglucose Lipopolysaccharides in Mycobacterium tuberculosis

Abstract

Mycobacteria produce two unusual polymethylated polysaccharides (PMPS), 3 the 3-O-methylmannose polysaccharides (MMP) (1-2) and the 6-O-methylglucosyl-containing lipopolysaccharides (MGLP) (3, 4). Both polysaccharides localize to the cytoplasm, where they have been postulated to regulate fatty acid synthesis by FAS-I as a consequence of their ability to form stable 1:1 complexes with long-chain fatty acids and acylcoenzyme A derivatives (5-9) (for a review, see Ref. 10). PMPS were also proposed to protect fatty acid products from degradation and to serve as general lipid carriers facilitating the synthesis of the very large and insoluble mycolic acid esters while at the same time increasing the tolerance of mycobacteria to high cytoplasmic concentrations of long-chain acyl-CoA derivatives (10 -12). PMPS were first isolated from Mycobacterium phlei, Mycobacterium smegmatis, and Mycobacterium tuberculosis in the 1960s (2-4), and much of the information we have about the structure, biosynthesis, and biological activities of these molecules comes from this early work. Others then revised the structure of MGLP and extended the analysis of these molecules to other mycobacterial species (13-15). The structures of MGLP and MMP are shown in Fig. 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. Termination of the elongation reaction occurs when the length of the chain is sufficient to confer on the polysaccharide fatty acid-binding properties (11-13 3-O-methylmannoses). At this stage, the chain is terminated with an unmethylated mannose because the acylCoA-bound oligosaccharides are no longer available as acceptors for the 3-O-methyltransferase.Knowledge of the initiation, elongation, and termination reactions involved in the biosynthesis of MGLP is more limited. A membrane-associated acyltransferase activity responsible for the transfer of acetyl, propionyl, isobutyryl, octanoyl, and succinyl groups from their respective acyl-CoA derivatives onto *

Identification of Genes Involved in the Biosynthesis of the Third and Fourth Sugars of the Methanococcus maripaludis Archaellin N-Linked Tetrasaccharide

“…In H. volcanii, the C-4 position in the hexuronic acid fourth sugar residue in the pentasaccharide N-glycan is methylated through the action of AglP, also identified as a SAM-dependent methyltransferase (49). Several bacterial O-antigenic polysaccharides also contain a variety of different sugars with O-methylation modifications at various positions (C-2, C-3, C-4, or C-6) catalyzed by SAM-dependent methyltransferases (57)(58)(59)(60). However, little sequence similarity is shared between the bacterial methyltransferases and the archaeal AglP and MMP1085.…”

Genetics of Mycobacterial Trehalose Metabolism

“…MGLPs are alpha-glucan oligomers consisting of 19 to 20 glucose residues, which are extensively methylated and acylated (76). MGLP biosynthesis involves the glucosyltransferase Rv3032, which can utilize UDP-glucose as well as ADPglucose as activated donor substrates (76). The synthetic lethal interaction was demonstrated by the inability to delete the genes treS and Rv3032 simultaneously in M. tuberculosis, while both genes individually are dispensable.…”

“…Finally, a synthetic lethal interaction of the GlgE pathway with an alternative pathway leading to production of methyl-branched alphaglucan derivatives, methylglucose lipopolysaccharides (MGLPs), has been revealed (23). MGLPs are alpha-glucan oligomers consisting of 19 to 20 glucose residues, which are extensively methylated and acylated (76). MGLP biosynthesis involves the glucosyltransferase Rv3032, which can utilize UDP-glucose as well as ADPglucose as activated donor substrates (76).…”

The α-Glucan Phosphorylase MalP of Corynebacterium glutamicum Is Subject to Transcriptional Regulation and Competitive Inhibition by ADP-Glucose

“…Also, mycobacteria such as Mycobacterium tuberculosis and M. smegmatis synthesize ␣-glucans not only via the well-known GlgC-GlgA pathway but also by two further pathways (79). The first alternative pathway proceeds via the rv3032-encoded glycosyltransferase in M. tuberculosis and is mainly involved in the formation of methylglucose lipopolysaccharides (80,81). The second alternative pathway for ␣-glucan formation in mycobacteria proceeds via the consecutive action of the maltokinase Pep1 and the maltosyltransferase GlgE (82,83).…”