Identification of a gene involved in the biosynthesis pathway of the terminal sugar of the archaellin N-linked tetrasaccharide in Methanococcus maripaludis

Study of the Differentially Expressed Genes in the Pomacea canaliculata Transcriptome after Treatment with Pedunsaponin A

Transcriptomes, genomes, and proteomes have played important roles in the search for drug targets. To determine the molluscicidal mechanism of pedunsaponin A against Pomacea canaliculata, RNA-seq technology was adopted to analyze the differentially expressed genes (DEGs) in the P. canaliculata transcriptome after treatment with pedunsaponin A. As a result, 533 DEGs were identified, among which 255 genes were significantly upregulated and 278 genes were significantly downregulated. According to the analysis of Gene Ontology (GO) functions, we found that the DEGs were significantly enriched in the viral life cycle, UDP-glucose 4-epimerase activity, guanylate cyclase activity, the cyclic guanosine monophosphate (cGMP) biosynthetic process, and the cGMP metabolic process. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway results showed that the DEGs were mainly involved in the hedgehog signaling pathway, phagosome, cytosolic DNA-sensing pathway, retinoic acid-inducible gene I like (RIG-I-like) receptor signaling pathway, bacterial secretion system, and nuclear factor-kappa B (NF-kappa B) signaling pathway. The above results indicated that pedunsaponin A causes a metabolic disorder, anomalous opening of membrane ion channels, and an imbalance in osmotic pressure between the interior and exterior of cells, eventually resulting in the death of cells involved in immune defense and influencing the immune response of P. canaliculata.

Identification and characterization of the 4-epimerase AglW from the archaeon Methanococcus maripaludis

Archaea are ubiquitous single-cell microorganisms that have often adapted to harsh conditions and play important roles in biogeochemical cycles with potential applications in biotechnology. Methanococcus maripaludis, a methane-producing archaeon, is motile through multiple archaella on its cell surface. The major structural proteins (archaellins) of the archaellum are glycoproteins, modified with N-linked tetrasaccharides that are essential for the proper assembly and function of archaella. The aglW gene, encoding the putative 4-epimerase AglW, plays a key role in the synthesis of the tetrasaccharide. The goal of our work was to biochemically demonstrate the 4-epimerase activity of AglW, and to develop assays to determine its substrate specificity and properties. We carried out assays using UDP-Galactose, UDP-Glucose, UDP-N-acetylglucosamine, UDP-N-acetylgalactosamine and N-acetylglucosamine/N-acetylgalactosamine-diphosphate - lipid as substrates, coupled with specific glycosyltransferases. We showed that AglW has a broad specificity towards UDP-sugars and that Tyr151 within a conserved YxxxK sequon is essential for the 4-epimerase function of AglW. The glycosyltransferase-coupled assays are generally useful for the identification and specificity studies of novel 4-epimerases.

Emerging facets of prokaryotic glycosylation

Glycosylation of proteins is one of the most prevalent post-translational modifications occurring in nature, with a wide repertoire of biological implications. Pathways for the main types of this modification, the N- and O-glycosylation, can be found in all three domains of life-the Eukarya, Bacteria and Archaea-thereby following common principles, which are valid also for lipopolysaccharides, lipooligosaccharides and glycopolymers. Thus, studies on any glycoconjugate can unravel novel facets of the still incompletely understood fundamentals of protein N- and O-glycosylation. While it is estimated that more than two-thirds of all eukaryotic proteins would be glycosylated, no such estimate is available for prokaryotic glycoproteins, whose understanding is lagging behind, mainly due to the enormous variability of their glycan structures and variations in the underlying glycosylation processes. Combining glycan structural information with bioinformatic, genetic, biochemical and enzymatic data has opened up an avenue for in-depth analyses of glycosylation processes as a basis for glycoengineering endeavours. Here, the common themes of glycosylation are conceptualised for the major classes of prokaryotic (i.e. bacterial and archaeal) glycoconjugates, with a special focus on glycosylated cell-surface proteins. We describe the current knowledge of biosynthesis and importance of these glycoconjugates in selected pathogenic and beneficial microbes.