Synthesis of GDP-mannose and mannosylglycerate from labeled mannose by genetically engineered Escherichia coli without loss of specific isotopic enrichment

Exploring the Potential of Corynebacterium glutamicum to Produce the Compatible Solute Mannosylglycerate

The compatible solute mannosylglycerate (MG) has exceptional properties in terms of protein stabilization and protection under salt, heat, and freeze-drying stresses as well as against protein aggregation. Due to these characteristics, MG possesses large potential for clinical and biotechnological applications. To achieve efficient MG production, Corynebacterium glutamicum was equipped with a bifunctional MG synthase (encoded by mgsD and catalyzing the condensation of 3-phosphoglycerate and GDP-mannose to MG) from Dehalococcoides mccartyi. The resulting strain C. glutamicum (pEKEx3 mgsD) intracellularly accumulated about 111 mM MG (60 ± 9 mg gCDW -1) with 2% glucose as a carbon source. To enable efficient mannose metabolization, the native manA gene, encoding mannose 6-phosphate isomerase, was overexpressed. Combined overexpression of manA and mgsD from two plasmids in C. glutamicum resulted in intracellular MG accumulation of up to ca. 329 mM [corresponding to 177 mg g cell dry weight (CDW) -1] with glucose, 314 mM (168 mg gCDW -1) with glucose plus mannose, and 328 mM (176 mg gCDW -1) with mannose as carbon source(s), respectively. The product was successfully extracted from cells by using a cold water shock, resulting in up to 5.5 mM MG (1.48 g L-1) in supernatants. The two-plasmid system was improved by integrating the mgsD gene into the manA-bearing plasmid and the resulting strain showed comparable production but faster growth. Repeated cycles of growth/production and extraction of MG in a bacterial milking-like experiment showed that cells could be recycled, which led to a cumulative MG production of 19.9 mM (5.34 g L-1). The results show that the newly constructed C. glutamicum strain produces MG from glucose and mannose and that a cold water shock enables extraction of MG from the cytosol into the medium.

Inactivation of phosphomannose isomerase gene abolishes sporulation and antibiotic production in Streptomyces coelicolor

Phosphomannose isomerases (PMIs) in bacteria and fungi catalyze the reversible conversion of D-fructose-6-phosphate to D-mannose-6-phosphate during biosynthesis of GDP-mannose, which is the main intermediate in the mannosylation of important cell wall components, glycoproteins, and certain glycolipids. In the present study, the kinetic parameters of PMI from Streptomyces coelicolor were obtained, and its function on antibiotic production and sporulation was studied. manA (SCO3025) encoding PMI in S. coelicolor was deleted by insertional inactivation. Its mutant (S. coelicolor∆manA) was found to exhibit a bld-like phenotype. Additionally, S. coelicolor∆manA failed to produce the antibiotics actinorhodin and red tripyrolle undecylprodigiosin in liquid media. To identify the function of manA, the gene was cloned and expressed in Escherichia coli BL21 (DE3). The purified recombinant ManA exhibited PMI activity (K(cat)/K(m) (mM(-1) s(-1) = 0.41 for D-mannose-6-phosphate), but failed to show GDP-D-mannose pyrophosphorylase [GMP (ManC)] activity. Complementation analysis with manA from S. coelicolor or E. coli resulted in the recovery of bld-like phenotype of S. coelicolor∆manA. SCO3026, another ORF that encodes a protein with sequence similarity towards bifunctional PMI and GMP, was also tested for its ability to function as an alternate ManA. However, the purified protein of SCO3026 failed to exhibit both PMI and GMP activity. The present study shows that enzymes involved in carbohydrate metabolism could control cellular differentiation as well as the production of secondary metabolites.

Identification of mannose uptake and catabolism genes in Corynebacterium glutamicum and genetic engineering for simultaneous utilization of mannose and glucose

Here, focus is on Corynebacterium glutamicum mannose metabolic genes with the aim to improve this industrially important microorganism's ability to ferment mannose present in mixed sugar substrates. cgR_0857 encodes C. glutamicum's protein with 36% amino acid sequence identity to mannose 6-phosphate isomerase encoded by manA of Escherichia coli. Its deletion mutant did not grow on mannose and exhibited noticeably reduced growth on glucose as sole carbon sources. In effect, C. glutamicum manA is not only essential for growth on mannose but also important in glucose metabolism. A double deletion mutant of genes encoding glucose and fructose permeases (ptsG and ptsF, respectively) of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) was not able to grow on mannose unlike the respective single deletion mutants with mannose utilization ability. A mutant deficient in ptsH, a general PTS gene, did not utilize mannose. These indicate that the glucose-PTS and fructose-PTS are responsible for mannose uptake in C. glutamicum. When cultured with a glucose and mannose mixture, mannose utilization of manA-overexpressing strain CRM1 was significantly higher than that of its wild-type counterpart, but with a strong preference for glucose. ptsF-overexpressing strain CRM2 co-utilized mannose and glucose, but at a total sugar consumption rate much lower than that of the wild-type strain and CRM1. Strain CRM3 overexpressing both manA and ptsF efficiently co-utilized mannose and glucose. Under oxygen-deprived conditions, high volumetric productivity of organic acids concomitant with the simultaneous consumption of the mixed sugars was achieved by the densely packed growth-arrested CRM3 cells.

Hexose/Pentose and Hexitol/Pentitol Metabolism

Escherichia coli and Salmonella enterica serovar Typhimurium exhibit a remarkable versatility in the usage of different sugars as the sole source of carbon and energy, reflecting their ability to make use of the digested meals of mammalia and of the ample offerings in the wild. Degradation of sugars starts with their energy-dependent uptake through the cytoplasmic membrane and is carried on further by specific enzymes in the cytoplasm, destined finally for degradation in central metabolic pathways. As variant as the different sugars are, the biochemical strategies to act on them are few. They include phosphorylation, keto-enol isomerization, oxido/reductions, and aldol cleavage. The catabolic repertoire for using carbohydrate sources is largely the same in E. coli and in serovar Typhimurium. Nonetheless, significant differences are found, even among the strains and substrains of each species. We have grouped the sugars to be discussed according to their first step in metabolism, which is their active transport, and follow their path to glycolysis, catalyzed by the sugar-specific enzymes. We will first discuss the phosphotransferase system (PTS) sugars, then the sugars transported by ATP-binding cassette (ABC) transporters, followed by those that are taken up via proton motive force (PMF)-dependent transporters. We have focused on the catabolism and pathway regulation of hexose and pentose monosaccharides as well as the corresponding sugar alcohols but have also included disaccharides and simple glycosides while excluding polysaccharide catabolism, except for maltodextrins.

Structural dissection and high-throughput screening of mannosylglycerate synthase

The enzymatic transfer of activated mannose yields mannosides in glycoconjugates and oligo- and polysaccharides. Yet, despite its biological necessity, the mechanism by which glycosyltransferases recognize mannose and catalyze its transfer to acceptor molecules is poorly understood. Here, we report broad high-throughput screening and kinetic analyses of both natural and synthetic substrates of Rhodothermus marinus mannosylglycerate synthase (MGS), which catalyzes the formation of the stress protectant 2-O-alpha-D-mannosyl glycerate. The sequence of MGS indicates that it is at the cusp of inverting and retaining transferases. The structures of apo MGS and complexes with donor and acceptor molecules, including GDP-mannose, combined with mutagenesis of the binding and catalytic sites, unveil the mannosyl transfer center. Nucleotide specificity is as important in GDP-D-mannose recognition as the nature of the donor sugar.

Identification of a GDP-mannose pyrophosphorylase gene from Sulfolobus solfataricus

An open reading frame (ORF) encoding a putative GDP-mannose pyrophosphorylase (SsoGMPP) was identified on the genome sequence of Sulfolobus solfataricus P2, the predicted gene product showing high amino acid sequence homology to several archaeal, bacterial, and eukaryal GDP-mannose pyrophosphorylases such as guanidine diphosphomannose pyrophosphorylases (GMPPs) from Saccharomyces cerevisiae and Arabidopsis thaliana. The sequence was PCR amplified from genomic DNA of S. solfataricus P2 and heterologous gene expression obtained as a fusion to glutathione S-transferase in Escherichia coli, under conditions suitable to reduce the formation of inclusion bodies. Specific assays performed at 60 degrees C revealed the presence of the archaeal synthesizing GDP-mannose enzyme activity in the cell extracts of the transformed E. coli. As a positive control, the same assays were performed at the mesophilic enzyme optimum temperature on the already characterized yeast recombinant GMPP. The recombinant protein was purified to homogeneity by glutathione sepharose affinity chromatography and its thermophilic nature could be verified. The enzyme was definitively identified by demonstrating its capability to catalyze also the reverse reaction of pyrophosphorolysis and, most interestingly, its high specificity for synthesizing GDP-mannose.

A gene from the mesophilic bacterium Dehalococcoides ethenogenes encodes a novel mannosylglycerate synthase

Mannosylglycerate (MG) is a common compatible solute found in thermophilic and hyperthermophilic prokaryotes. In this study we characterized a mesophilic and bifunctional mannosylglycerate synthase (MGSD) encoded in the genome of the bacterium Dehalococcoides ethenogenes. mgsD encodes two domains with extensive homology to mannosyl-3-phosphoglycerate synthase (MPGS, EC 2.4.1.217) and to mannosyl-3-phosphoglycerate phosphatase (MPGP, EC 3.1.3.70), which catalyze the consecutive synthesis and dephosphorylation of mannosyl-3-phosphoglycerate to yield MG in Pyrococcus horikoshii, Thermus thermophilus, and Rhodothermus marinus. The bifunctional MGSD was overproduced in Escherichia coli, and we confirmed the combined MPGS and MPGP activities of the recombinant enzyme. The optimum activity of the enzyme was at 50 degrees C. To examine the properties of each catalytic domain of MGSD, we expressed them separately in E. coli. The monofunctional MPGS was unstable, while the MPGP was stable and was characterized. Dehalococcoides ethenogenes cannot be grown sufficiently to identify intracellular compatible solutes, and E. coli harboring MGSD did not accumulate MG. However, Saccharomyces cerevisiae expressing mgsD accumulated MG, confirming that this gene product can synthesize this compatible solute and arguing for a role in osmotic adjustment in the natural host. We did not detect MGSD activity in cell extracts of S. cerevisiae. Here we describe the first gene and enzyme for the synthesis of MG from a mesophilic microorganism and discuss the possible evolution of this bifunctional MGSD by lateral gene transfer from thermophilic and hyperthermophilic organisms.