Mannose metabolism is required for mycobacterial growth.

Mycobacteria are the causative agents of tuberculosis and several other significant diseases in humans. All species of mycobacteria synthesize abundant cell-wall mannolipids (phosphatidylinositol mannosides, lipoarabinomannan), a cytoplasmic methylmannose polysaccharide and O-mannosylated glycoproteins. To investigate whether these molecules are essential for mycobacterial growth, we have generated a Mycobacterium smegmatis mannose auxotroph by targeted deletion of the gene encoding phosphomannose isomerase (PMI). The PMI deletion mutant displayed a mild hyperseptation phenotype, but grew normally in media containing an exogenous source of mannose. When this mutant was suspended in media without mannose, ongoing synthesis of both the mannolipids and methylmannose polysaccharides was halted and the hyperseptation phenotype became more pronounced. These changes preceded a dramatic loss of viability after 10 h in mannose-free media. Mannose starvation did not lead to detectable changes in cell-wall ultrastructure or permeability to hydrophobic drugs, or to changes in the rate of biosynthesis of other plasma-membrane or wall-associated phospholipids. These results show that mannose metabolism is required for growth of M. smegmatis and that one or more mannose-containing molecules may play a role in regulating septation and cell division in these bacteria

Methylation of GPLs in Mycobacterium smegmatis and Mycobacterium avium

Several species of mycobacteria express abundant glycopeptidolipids (GPLs) on the surfaces of their cells. The GPLs are glycolipids that contain modified sugars including acetylated 6-deoxy-talose and methylated rhamnose. Four methyltransferases have been implicated in the synthesis of the GPLs of Mycobacterium smegmatis and Mycobacterium avium. A rhamnosyl 3-O-methytransferase and a fatty acid methyltransferase of M. smegmatis have been previously characterized. In this paper, we characterize the methyltransferases that are responsible for modifying the hydroxyl groups at positions 2 and 4 of rhamnose and propose the biosynthetic sequence of GPL trimethylrhamnose formation. The analysis of M. avium genes through the creation of specific mutants is technically difficult; therefore, an alternative approach to determine the function of putative methyltransferases of M. avium was undertaken. Complementation of M. smegmatis methyltransferase mutants with M. avium genes revealed that MtfC and MtfB of the latter species have 4-O-methyltransferase activity and that MtfD is a 3-O-methyltransferase which can modify rhamnose of GPLs in M. smegmatis

Binaphthyl-anchored antibacterial tripeptide derivatives with hydrophobic C-terminal amino acid variations

The facile synthesis of seven new dicationic tripeptide benzyl ester derivatives, with hydrophobic group variations in the C-terminal amino acid component, is described. Moderate to good activity was seen against Gram-positive bacteria in vitro. One cyclohexyl-substituted compound 2c was tested more widely and showed good potency (MIC values ranging from 2–4 µg/mL) against antibiotic-resistant strains of Staphylococcus aureus and Enterococci (VRE, VSE), and against Staphylococcus epidermidis

Structure and Function Characterization of the a1a2 Motifs of Streptococcus pyogenes M Protein in Human Plasminogen Binding

Plasminogen (Plg)-binding M protein (PAM) is a group A streptococcal cell surface receptor that is crucial for bacterial virulence. Previous studies revealed that, by binding to the kringle 2 (KR2) domain of host Plg, the pathogen attains a proteolytic microenvironment on the cell surface that facilitates its dissemination from the primary infection site. Each of the PAM molecules in their dimeric assembly consists of two Plg binding motifs (called the a1 and a2 repeats). To date, the molecular interactions between the a1 repeat and KR2 have been structurally characterized, whereas the role of the a2 repeat is less well defined. Here, we report the 1.7-Å x-ray crystal structure of KR2 in complex with a monomeric PAM peptide that contains both the a1 and a2 motifs. The structure reveals how the PAM peptide forms key interactions simultaneously with two KR2 via the high-affinity lysine isosteres within the a1a2 motifs. Further studies, through combined mutagenesis and functional characterization, show that a2 is a stronger KR2 binder than a1, suggesting that these two motifs may play discrete roles in mediating the final PAM-Plg assembly