Clostridioides difficile cd2775 Encodes a Unique Mannosyl-1-Phosphotransferase for Polysaccharide II Biosynthesis

Polysaccharide biosynthetic pathway profiling and homologous expression of the phosphomannomutase gene in Sanghuangporus sanghuang based on multi-omics analysis

Sanghuangprous sanghuang is a valuable medicinal macrofungus with abundant active metabolites. Improvement of macrofungal strains to increase the production of metabolites, especially polysaccharides, has become a research priority. In this study, we sequenced the whole genome and transcriptome of S. sanghuang SS-01 strain, identified the genes of key enzymes involved in the polysaccharide synthetic pathway, and constructed a homologous recombinant strain to increase S. sanghuang polysaccharide (SSP) yield for the first time. The assembled genome is 37.83 Mb with 22 contigs, encoding 7266 predicted genes. Forty putative genes related to sugar metabolism were identified, and the proposed SSP synthetic pathway was mapped. Transcriptional profiling was performed under different culture conditions to investigate the importance of key gene expression on SSP content. The phosphomannomutase (SsPMM) gene, which showed a strong correlation with SSP production, was identified from six differentially expressed genes. Based on the polyethylene glycol-mediated protoplast transformation system, a homologous recombinant strain (RsPMM) was obtained. The upregulated expression level of SsPMM (1.39-fold) was associated with significantly higher SSP content (1.46-fold) in RsPMM compared to the wild-type strain. Our findings provide an effective approach to increase polysaccharide production and facilitate the understanding of metabolite synthesis mechanisms in S. sanghuang.

Proteome-wide bioinformatic annotation and functional validation of the monotopic phosphoglycosyl transferase superfamily

Phosphoglycosyl transferases (PGTs) are membrane proteins that initiate glycoconjugate biosynthesis by transferring a phospho-sugar moiety from a soluble nucleoside diphosphate sugar to a membrane-embedded polyprenol phosphate acceptor. The centrality of PGTs in complex glycan assembly and the current lack of functional information make these enzymes high-value targets for biochemical investigation. In particular, the small monotopic PGT family is exclusively bacterial and represents the minimal functional unit of the monotopic PGT superfamily. Here, we combine a sequence similarity network analysis with a generalizable, luminescence-based activity assay to probe the substrate specificity of this family of monoPGTs in the bacterial cell-membrane fraction. This strategy allows us to identify specificity on a far more significant scale than previously achievable and correlate preferred substrate specificities with predicted structural differences within the conserved monoPGT fold. Finally, we present the proof-of-concept for a small-scale inhibitor screen (eight nucleoside analogs) with four monoPGTs of diverse substrate specificity, thus building a foundation for future inhibitor discovery initiatives.

Application of bioanalytical and computational methods in decoding the roles of glycans in host-pathogen interactions

Host-pathogen interactions (HPIs) are complex processes that require tight regulation. A common regulatory mechanism of HPIs is through glycans of either host cells or pathogens. Due to their diverse sequences, complex structures, and conformations, studies of glycans require highly sensitive and powerful tools. Recent improvements in technology have enabled the application of many bioanalytical techniques and modeling methods to investigate glycans and their mechanisms in HPIs. This mini-review highlights how these advances have been used to understand the role glycans play in HPIs in the past 2 years.

Structure and synthesis of a vaccine and diagnostic target for Enterocloster bolteae, an autism-associated gut pathogen – Part II

Enterocloster bolteae (formerly known as Clostridium bolteae) is a gastro-intestinal pathogenic bacterium often detected in the fecal microbiome of children in the autism spectrum. E. bolteae excretes metabolites that are thought to act as neurotoxins. This study is an update of our first E. bolteae investigation that discovered an immunogenic polysaccharide. Through a combination of chemical derivatizations/degradations, spectrometry and spectroscopy techniques, a polysaccharide composed of disaccharide repeating blocks comprised of 3-linked β-d-ribofuranose and 4-linked α-l-rhamnopyranose, [→3)-β-D-Ribf-(1 → 4)-α-L-Rhap-(1→]_n, was identified. To confirm the structure, and to provide material for subsequent investigations, the chemical synthesis of a corresponding linker-equipped tetrasaccharide, β-D-Ribf-(1 → 4)-α-L-Rhap-(1 → 3)-β-D-Ribf-(1 → 4)-α-L-Rhap-(1→O(CH₂)₈N₃, is also described. Research tools based on this immunogenic glycan structure can form the foundation for serotype classification, diagnostic/vaccine targets and clinical studies into the hypothesized role of E. bolteae in the onset/augmentation of autism related conditions in children.

Recent progress in synthesis of carbohydrates with sugar nucleotide-dependent glycosyltransferases

Sugar nucleotide-dependent glycosyltransferases (GTs) are key enzymes that catalyze the formation of glycosidic bonds in nature. They have been increasingly applied in the synthesis of complex carbohydrates and glycoconjugates with or without in situ generation of sugar nucleotides. Human GTs are becoming more accessible and new bacterial GTs have been identified and characterized. An increasing number of crystal structures elucidated for GTs from mammalian and bacterial sources facilitate structure-based design of mutants as improved catalysts for synthesis. Automated platforms have also been developed for chemoenzymatic synthesis of carbohydrates. Recent progress in applying sugar nucleotide-dependent GTs in enzymatic and chemoenzymatic synthesis of mammalian glycans and glycoconjugates, bacterial surface glycans, and glycosylated natural products from bacteria and plants are reviewed.

Nucleotide Sugars in Chemistry and Biology

Nucleotide sugars have essential roles in every living creature. They are the building blocks of the biosynthesis of carbohydrates and their conjugates. They are involved in processes that are targets for drug development, and their analogs are potential inhibitors of these processes. Drug development requires efficient methods for the synthesis of oligosaccharides and nucleotide sugar building blocks as well as of modified structures as potential inhibitors. It requires also understanding the details of biological and chemical processes as well as the reactivity and reactions under different conditions. This article addresses all these issues by giving a broad overview on nucleotide sugars in biological and chemical reactions. As the background for the topic, glycosylation reactions in mammalian and bacterial cells are briefly discussed. In the following sections, structures and biosynthetic routes for nucleotide sugars, as well as the mechanisms of action of nucleotide sugar-utilizing enzymes, are discussed. Chemical topics include the reactivity and chemical synthesis methods. Finally, the enzymatic in vitro synthesis of nucleotide sugars and the utilization of enzyme cascades in the synthesis of nucleotide sugars and oligosaccharides are briefly discussed.

Synthesis of selected unnatural sugar nucleotides for biotechnological applications

Sugar nucleotides are the principal building blocks for the synthesis of most complex carbohydrates and are crucial intermediates in carbohydrate metabolism. Uridine diphosphate (UDP) monosaccharides are among the most common sugar nucleotide donors and are transferred to glycosyl acceptors by glycosyltransferases or synthases in glycan biosynthetic pathways. These natural nucleotide donors have great biological importance, however, the synthesis and application of unnatural sugar nucleotides that are not available from in vivo biosynthesis are not well explored. In this review, we summarize the progress in the preparation of unnatural sugar nucleotides, in particular, the widely studied UDP-GlcNAc/GalNAc analogs. We focus on the "two-block" synthetic pathway that is initiated from monosaccharides, in which the first block is the synthesis of sugar-1-phosphate and the second block is the diphosphate bond formation. The biotechnological applications of these unnatural sugar nucleotides showing their physiological and pharmacological potential are discussed.