Chemical Synthesis of a Colanic Acid Hexasaccharide

Shotgun proteomic analyses of Pseudomonas species isolated from fish products

Numerous Pseudomonas species can infect aquatic animals, such as farmed rainbow trout, sea trout, sea bass, and sea bream, by causing disease or stress reactions. In aquaculture facilities, a number of Pseudomonas species have been isolated and identified as the main pathogens. The present study describes the characterization of 18 Pseudomonas strains, isolated from fish products using shotgun proteomics. The bacterial proteomes obtained were further analyzed to identify the main functional pathway proteins involved. In addition, this study revealed the presence of 1015 non-redundant peptides related to virulence factors. An additional 25 species-specific peptides were identified as putative Pseudomonas spp. biomarkers. The results constitute the largest dataset, described thus far for the rapid identification and characterization of Pseudomonas species present in edible fish; furthermore, these data can provide the basis for further research into the development of new therapies against these harmful pathogens.

Engineering Escherichia coli to Efficiently Produce Colanic Acid with Low Molecular Mass and Viscosity

Colanic acid (CA) is exopolysaccharide that presents growing potential in the food and healthcare industry as a versatile polymer. Previously, we have constructed the Escherichia coli strain WWM16 which can efficiently produce CA. In this study, WWM16 has been further engineered to produce a higher yield of CA with low molecular mass and viscosity. The gene mcbR encoding a transcriptional factor, and the genes opgD, opgG, and opgH related to the biosynthesis of osmoregulated periplasmic glucans were deleted in E. coli WWM16, and the resulting strain WWM166 produced 18.1 g/L CA. The expression level of wcaD encoding the polymerase in WWM166 was downregulated using CRISPRi. As a result, the strain WWM166/pWpD1 could produce 49.9 g/L CA with lower molecular mass. CA products were purified from both WWM166 and WWM166/pWpD1, and their molecular mass, viscosity, fluidity, hygroscopicity, and antioxidant activity were determined and compared. These findings demonstrate the potential application of CA with different molecular masses to prolong life and protect skin in the food and cosmetic industries.

Synthesis and application of bacterial exopolysaccharides

Exopolysaccharides are produced and excreted by bacteria in the generation of biofilms to provide a protective environment. These polysaccharides are generally generated as heterogeneous polymers of varying length, featuring diverse substitution patterns. To obtain well-defined fragments of these polysaccharides, organic synthesis often is the method of choice, as it allows for full control over chain length and the installation of a pre-determined substitution pattern. This review presents several recent syntheses of exopolysaccharide fragments of Pseudomonas aeruginosa and Staphylococcus aureus and illustrates how these have been used to study biosynthesis enzymes and generate synthetic glycoconjugate vaccines.

Rational design of GDP‑D‑mannose mannosyl hydrolase for microbial L‑fucose production

BACKGROUND

L‑Fucose is a rare sugar that has beneficial biological activities, and its industrial production is mainly achieved with brown algae through acidic/enzymatic fucoidan hydrolysis and a cumbersome purification process. Fucoidan is synthesized through the condensation of a key substance, guanosine 5'‑diphosphate (GDP)‑L‑fucose. Therefore, a more direct approach for biomanufacturing L‑fucose could be the enzymatic degradation of GDP‑L‑fucose. However, no native enzyme is known to efficiently catalyze this reaction. Therefore, it would be a feasible solution to engineering an enzyme with similar function to hydrolyze GDP‑L‑fucose.

RESULTS

Herein, we constructed a de novo L‑fucose synthetic route in Bacillus subtilis by introducing heterologous GDP‑L‑fucose synthesis pathway and engineering GDP‑mannose mannosyl hydrolase (WcaH). WcaH displays a high binding affinity but low catalytic activity for GDP‑L‑fucose, therefore, a substrate simulation‑based structural analysis of the catalytic center was employed for the rational design and mutagenesis of selected positions on WcaH to enhance its GDP‑L‑fucose‑splitting efficiency. Enzyme mutants were evaluated in vivo by inserting them into an artificial metabolic pathway that enabled B. subtilis to yield L‑fucose. WcaH^R36Y/N38R was found to produce 1.6 g/L L‑fucose during shake‑flask growth, which was 67.3% higher than that achieved by wild‑type WcaH. The accumulated L‑fucose concentration in a 5 L bioreactor reached 6.4 g/L.

CONCLUSIONS

In this study, we established a novel microbial engineering platform for the fermentation production of L‑fucose. Additionally, we found an efficient GDP‑mannose mannosyl hydrolase mutant for L‑fucose biosynthesis that directly hydrolyzes GDP‑L‑fucose. The engineered strain system established in this study is expected to provide new solutions for L‑fucose or its high value‑added derivatives production.

Chemical synthesis of oligosaccharides and their application in new drug research

Oligosaccharides are the ubiquitous molecules of life. In order to translate human bioglycosylation into clinical applications, homogeneous samples of oligosaccharides and glycoconjugates can be obtained by chemical, enzymatic or other biological methods for systematic studies. However, the structural complexity and diversity of glycans and their conjugates present a major challenge for the synthesis of such molecules. This review summarizes the chemical synthesis methods of oligosaccharides, the application of oligosaccharides in the field of medicinal chemistry according to their related biological activities, and shows the great prospect of oligosaccharides in the field of pharmaceutical chemistry.