Various mechanisms of protein cell surface display have evolved during bacterial evolution. Several Gram-positive bacteria employ S-layer homology (SLH) domain-mediated sorting of cell-surface proteins and concomitantly engage a pyruvylated secondary cell-wall polymer as a cell-wall ligand. Specifically, pyruvate ketal linked to β-D-ManNAc is regarded as an indispensable epitope in this cell-surface display mechanism. That secondary cell wall polymer (SCWP) pyruvylation and SLH domain-containing proteins are functionally coupled is supported by the presence of an ortholog of the predicted pyruvyltransferase CsaB in bacterial genomes, such as those of Bacillus anthracis and Paenibacillus alvei. The P. alvei SCWP, consisting of pyruvylated disaccharide repeats [→4)-β-D-GlcNAc-(1→3)-4,6-Pyr-β-D-ManNAc-(1→] serves as a model to investigate the widely unexplored pyruvylation reaction. Here, we reconstituted the underlying enzymatic pathway in vitro in combination with synthesized compounds, used mass spectrometry, and nuclear magnetic resonance spectroscopy for product characterization, and found that CsaB-catalyzed pyruvylation of β-D-ManNAc occurs at the stage of the lipid-linked repeat. We produced the P. alvei TagA (PAV_RS07420) and CsaB (PAV_RS07425) enzymes as recombinant, tagged proteins, and using a synthetic 11-phenoxyundecyl-diphosphoryl-α-GlcNAc acceptor, we uncovered that TagA is an inverting UDP-α-D-ManNAc:GlcNAc-lipid carrier transferase, and that CsaB is a pyruvyltransferase, with synthetic UDP-α-D-ManNAc and phosphoenolpyruvate serving as donor substrates. Next, to substitute for the UDP-α-D-ManNAc substrate, the recombinant UDP-GlcNAc-2-epimerase MnaA (PAV_RS07610) of P. alvei was included in this in vitro reconstitution system. When all three enzymes, their substrates and the lipid-linked GlcNAc primer were combined in a one-pot reaction, a lipid-linked SCWP repeat precursor analog was obtained. This work highlights the biochemical basis of SCWP biosynthesis and bacterial pyruvyl transfer.

The demand to develop and produce eco-friendly alternatives for food packaging is increasing. The huge negative impact that the disposal of so-called “single-use plastics” has on the environment is propelling the market to search for new solutions, and requires initiatives to drive faster responses from the scientific community, the industry, and governmental bodies for the adoption and implementation of new materials. Bioplastics are an alternative group of materials that are partly or entirely produced from renewable sources. Some bioplastics are biodegradable or even compostable under the right conditions. This review presents the different properties of these materials, mechanisms of biodegradation, and their environmental impact, but also presents a holistic overview of the most important bioplastics available in the market and their potential application for food packaging, consumer perception of the bioplastics, regulatory aspects, and future challenges.

Benzyloxycarbonyl can be used as participating group for the diastereoselective glycosylation of base-labile products and the synthesis of glycosyl esters.

A disaccharide implicated in anchoring of bacterial Surface-layer proteins to secondary cell wall glycopolymers has been prepared by glycosylation of a protected N-acetyl glucosamine acceptor with a glucopyranosyl donor to generate the β-(1→4)-linkage. Subsequent inversion of the configuration and azide introduction at position 2 with triflic anhydride, however, led to formation of a tetrazole derivative. Alternatively, displacement of a 2-O-mesylate by sodium azide, reduction and N-acetylation enabled the conversion into the distal N-acetyl-β-Dmannosamine residue. Pyruvylation of the latter unit and global deprotection afforded the disaccharide repeating unit from Paenibacillus alvei as a ligand for crystallographic and binding studies. β4 β3 α β4