Identification and characterization of novel small molecule inhibitors of the acetyltransferase activity of Escherichia coli N-acetylglucosamine-1-phosphate-uridyltransferase/glucosamine-1-phosphate-acetyltransferase (GlmU)

Biosynthesis of uridine diphosphate N-Acetylglucosamine: An underexploited pathway in the search for novel antibiotics?

Although the prevalence of antibiotic resistance is increasing at an alarming rate, there are a dwindling number of effective antibiotics available. Thus, the development of novel antibacterial agents should be of utmost importance. Peptidoglycan biosynthesis has been and is still an attractive source for antibiotic targets; however, there are several components that remain underexploited. In this review, we examine the enzymes involved in the biosynthesis of one such component, UDP-N-acetylglucosamine, an essential building block and precursor of bacterial peptidoglycan. Furthermore, given the presence of a similar biosynthesis pathway in eukaryotes, we discuss the current knowledge on the differences and similarities between the bacterial and eukaryotic enzymes. Finally, this review also summarises the recent advances made in the development of inhibitors targeting the bacterial enzymes.

GlmU inhibitor from the roots of Euphorbia ebracteolata as an anti-tuberculosis agent

Ebractenoid F was identified to be a GlmU inhibitor from Euphorbia ebracteolata, which could inhibit the cell wall biosynthesis of M. tb H37Ra, along with the biofilm formation.

Chemical Biology Tools for Modulating and Visualizing Gram-Negative Bacterial Surface Polysaccharides

Bacterial cells present a wide diversity of saccharides that decorate the cell surface and help mediate interactions with the environment. Many Gram-negative cells express O-antigens, which are long sugar polymers that makeup the distal portion of lipopolysaccharide (LPS) that constitutes the surface of the outer membrane. This review highlights chemical biology tools that have been developed in recent years to facilitate the modulation of O-antigen synthesis and composition, as well as related bacterial polysaccharide pathways, and the detection of unique glycan sequences. Advances in the biochemistry and structural biology of O-antigen biosynthetic machinery are also described, which provide guidance for the design of novel chemical and biomolecular probes. Many of the tools noted here have not yet been utilized in biological systems and offer researchers the opportunity to investigate the complex sugar architecture of Gram-negative cells.

Functional analysis and enzyme characterization of Mannose-1-phosphate guanylyl transferase (ManB) from Mycobacterium tuberculosis

Mycobacterium tuberculosis cell wall consist variety of mannose containing glycoconjugates including lipomannan (LM) and lipoarabinomannan (LAM). These lipoglycans are involved in cell wall integrity and play role in virulence of M. tuberculosis by modulating host immune response. GDP-mannose, required for the synthesis of lipoglycans, is catalyzed by enzyme Mannose-1-phosphate guanylyl transferase (ManB). The enzyme with similar function has been studied in variety of species of prokaryotes and eukaryotes. However, biological role of ManB and its enzymatic activity remains uncharacterized in M. tuberculosis. In present study, we elucidated the role of enzyme by constructing manB knockdown strain of M. tuberculosis H37Ra. The manB knockdown decreased the cell growth and also effected the morphology of M. tuberculosis by altering the permeability of cell membrane. These findings provide the understanding on ManB function and suggesting that ManB could be the potential target for novel anti-tuberculosis drug. Furthermore, we also characterized ManB enzyme by establishing 96 well plate colorimetric assay and determined the kinetic properties including initial velocity, optimum temperature, optimum pH and other kinetic parameters. Our established assay will be helpful for further high throughput screening of potential inhibitors against ManB.

Enhancement of Production of D-Glucosamine in Escherichia coli by Blocking Three Pathways Involved in the Consumption of GlcN and GlcNAc

D-Glucosamine is a commonly used dietary supplement that promotes cartilage health in humans. Metabolic flux analysis showed that D-glucosamine production could be increased by blocking three pathways involved in the consumption of glucosamine-6-phosphate and acetylglucosamine-6-phosphate. By homologous single-exchange, two key genes (nanE and murQ) of Escherichia coli BL21 were knocked out, respectively. The D-glucosamine yields of the engineered strains E. coli BL21ΔmurQ and E. coli BL21ΔnanE represented increases by factors of 2.14 and 1.79, respectively. Meanwhile, for bifunctional gene glmU, we only knocked out its glucosamine-1-phosphate acetyltransferase domain by 3D structural analysis to keep the engineered strain E. coli BL21glmU-Δgpa survival, which resulted in an increase in the production of D-glucosamine by a factor of 2.16. Moreover, for further increasing D-glucosamine production, two genes encoding rate-limiting enzymes, named glmS and gna1, were coexpressed by an RBS sequence in those engineered strains. The total concentrations of D-glucosamine in E. coli BL21 glmU-Δgpa', E. coli BL21ΔmurQ', and E. coli BL21ΔnanE' were 2.65 g/L, 1.73 g/L, and 1.38 g/L, which represented increases by factors of 8.83, 5.76, and 3.3, respectively.

The Inhibitory Effect of GlmU Acetyltransferase Inhibitor TPSA on Mycobacterium tuberculosis May Be Affected Due to Its Methylation by Methyltransferase Rv0560c

Mycobacterium tuberculosis bifunctional enzyme GlmU is a novel target for anti-TB drugs and is involved in glycosyl donor UDP-N-acetylglucosamine biosynthesis. Here, we found that TPSA (2-[5-(2-{[4-(2-thienyl)-2-pyrimidinyl]sulfanyl}acetyl)-2-thienyl]acetic acid) was a novel inhibitor for GlmU acetyltransferase activity (IC₅₀: 5.3 μM). The interaction sites of GlmU and TPSA by molecular docking were confirmed by site-directed mutagenesis. TPSA showed an inhibitory effect on Mtb H37Ra growth and intracellular H37Ra in macrophage cells (MIC: 66.5 μM). To investigate why TPSA at a higher concentration (66.5 μM) was able to inhibit H37Ra growth, proteome and transcriptome of H37Ra treated with TPSA were analyzed. The expression of two methyltransferases MRA_0565 (Rv0558) and MRA_0567 (Rv0560c) were markedly increased. TPSA was pre-incubated with purified Rv0558 and Rv0560c in the presence of S-adenosylmethionine (methyl donor) respectively, resulting in its decreased inhibitory effect of GlmU on acetyltransferase activity. The inhibition of TPSA on growth of H37Ra with overexpressed Rv0558 and Rv0560c was reduced. These implied that methyltransferases could modify TPSA. The methylation of TPSA catalyzed by Rv0560c was subsequently confirmed by LC-MS. Therefore, TPSA as a GlmU acetyltransferase activity inhibitor may offer a structural basis for new anti-tuberculosis drugs. TPSA needs to be modified further by some groups to prevent its methylation by methyltransferases.

Synthesis and antimicrobial activity of 6-sulfo-6-deoxy-D-glucosamine and its derivatives

6-Sulfo-6-deoxy-D-glucosamine (GlcN6S), 6-sulfo-6-deoxy-D-glucosaminitol (ADGS) and their N-acetyl and methyl ester derivatives have been synthesized and tested as inhibitors of enzymes catalyzing reactions of the UDP-GlcNAc pathway in bacteria and yeasts. GlcN6S and ADGS at micromolar concentrations inhibited glucosamine-6-phosphate (GlcN6P) synthase of microbial origin. The former was also inhibitory towards fungal GlcN6P N-acetyl transferase, but at millimolar concentrations. Both compounds and their N-acetyl derivatives exhibited antimicrobial in vitro activity, with MICs in the 0.125-2.0 mg mL^-1 range. Antibacterial but not antifungal activity of GlcN6S was potentiated by D-glucosamine and a synergistic antibacterial effect was observed for combination of ADGP and a dipeptide Nva-FMDP.