A New Look at the Enterobacterial Common Antigen Forms Obtained during Rough Lipopolysaccharides Purification

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

Metabolic Usage and Glycan Destinations of GlcNAz in E. coli

Bacteria use a diverse range of carbohydrates to generate a profusion of glycans, with amino sugars, such as N-acetylglucosamine (GlcNAc), being prevalent in the cell wall and in many exopolysaccharides. The primary substrate for GlcNAc-containing glycans, UDP-GlcNAc, is the product of the bacterial hexosamine pathway and a key target for bacterial metabolic glycan engineering. Using the strategy of expressing NahK, to circumvent the hexosamine pathway, it is possible to directly feed the analogue of GlcNAc, N-azidoacetylglucosamine (GlcNAz), for metabolic labeling in Escherichia coli. The cytosolic production of UDP-GlcNAz was confirmed by using fluorescence-assisted polyacrylamide gel electrophoresis. The key question of where GlcNAz is incorporated was interrogated by analyzing potential sites including peptidoglycan (PGN), the biofilm-related exopolysaccharide poly-β-1,6-N-acetylglucosamine (PNAG), lipopolysaccharide (LPS), and the enterobacterial common antigen (ECA). The highest levels of incorporation were observed in PGN with lower levels in PNAG and no observable incorporation in LPS or ECA. The promiscuity of the PNAG synthase (PgaCD) toward UDP-GlcNAz in vitro and the lack of undecaprenyl-pyrophosphoryl-GlcNAz intermediates generated in vivo confirmed the incorporation preferences. The results of this work will guide the future development of carbohydrate-based probes and metabolic engineering strategies.