Elucidation of the Lipopolysaccharide Core Structures of Bacteria of the GenusProvidencia

Pyruvate Substitutions on Glycoconjugates

Glycoconjugates are the most diverse biomolecules of life. Mostly located at the cell surface, they translate into cell-specific "barcodes" and offer a vast repertoire of functions, including support of cellular physiology, lifestyle, and pathogenicity. Functions can be fine-tuned by non-carbohydrate modifications on the constituting monosaccharides. Among these modifications is pyruvylation, which is present either in enol or ketal form. The most commonly best-understood example of pyruvylation is enol-pyruvylation of N-acetylglucosamine, which occurs at an early stage in the biosynthesis of the bacterial cell wall component peptidoglycan. Ketal-pyruvylation, in contrast, is present in diverse classes of glycoconjugates, from bacteria to algae to yeast-but not in humans. Mild purification strategies preventing the loss of the acid-labile ketal-pyruvyl group have led to a collection of elucidated pyruvylated glycan structures. However, knowledge of involved pyruvyltransferases creating a ring structure on various monosaccharides is scarce, mainly due to the lack of knowledge of fingerprint motifs of these enzymes and the unavailability of genome sequences of the organisms undergoing pyruvylation. This review compiles the current information on the widespread but under-investigated ketal-pyruvylation of monosaccharides, starting with different classes of pyruvylated glycoconjugates and associated functions, leading to pyruvyltransferases, their specificity and sequence space, and insight into pyruvate analytics.

Structure of the O-polysaccharide of Providencia alcalifaciens O2 containing ascarylose and N-(L-alanyl)-D-glucosamine

The O-polysaccharide was obtained by degradation of the lipopolysaccharide of Providencia alcalifaciens O2 under mild acidic conditions followed by GPC. The polysaccharide was found to contain two unusual components: 3,6-dideoxy-L-arabino-hexose (ascarylose, Asc) and 2-(L-alanyl)amino-2-deoxy-D-glucose (GlcNAla). Ascarylose was partially split off during lipopolysaccharide degradation and could be eliminated completely by selective acid hydrolysis, which also partially cleaved the β-GAlNAc-(1 → 6) linkage. The following structure of the branched pentasaccharide repeating unit was established by (1)H and (13)C NMR spectroscopy of the O-polysaccharide and O-deacetylated polysaccharide, as well as products of partial acid hydrolysis: α-Ascp-(1 → 4)-α-D-GlcpA-(1 → 4) → 6)-β-D-GlcpNAla-(1 → 4)-β-D-GlpA-(1 → 3)-β-D-GalpNAc-(1 → ~60% OAc--3).

Structure of the O-polysaccharide from the lipopolysaccharide of Providencia alcalifaciens O33

Mild acid degradation of the lipopolysaccharide from Providencia alcalifaciens O33 resulted in an O-polysaccharide along with core and O-unit-bearing core oligosaccharides. Composition of the oligosaccharides was inferred by ESI mass spectrometry. Based on sugar and methylation analyses, Smith degradation and (1)H and (13)C NMR spectroscopy data, the following structure of the tetrasaccharide O-unit of the O-polysaccharide was established: Another O-polysaccharide structure has been reported earlier for Providencia stuartii О33 but later found to belong to a P. stuartii О52 strain.

Functional identification of Proteus mirabilis eptC gene encoding a core lipopolysaccharide phosphoethanolamine transferase

By comparison of the Proteus mirabilis HI4320 genome with known lipopolysaccharide (LPS) phosphoethanolamine transferases, three putative candidates (PMI3040, PMI3576, and PMI3104) were identified. One of them, eptC (PMI3104) was able to modify the LPS of two defined non-polar core LPS mutants of Klebsiella pneumoniae that we use as surrogate substrates. Mass spectrometry and nuclear magnetic resonance showed that eptC directs the incorporation of phosphoethanolamine to the O-6 of l-glycero-d-mano-heptose II. The eptC gene is found in all the P. mirabilis strains analyzed in this study. Putative eptC homologues were found for only two additional genera of the Enterobacteriaceae family, Photobacterium and Providencia. The data obtained in this work supports the role of the eptC (PMI3104) product in the transfer of PEtN to the O-6 of l,d-HepII in P. mirabilis strains.

Structural, serological, and genetic characterization of the O-antigen of Providencia alcalifaciens O40

The O-polysaccharide chain of the lipopolysaccharide (O-antigen) on the bacterial cell surface is one of the most structurally variable cell components and serves as a basis for serotyping of Gram-negative bacteria, including human opportunistic pathogens of the genus Providencia. In this work, the O-antigen of Providencia alcalifaciens O40 was obtained by mild acid degradation of the isolated lipopolysaccharide and studied by chemical methods and high-resolution NMR spectroscopy. The following structure of the O-polysaccharide was established: →4)-β-D-Quip3NFo-(1→3)-α-D-Galp-(1→3)-β-D-GlcpA-(1→3)-β-D-GalpNAc-(1→, where GlcA stands for glucuronic acid and Qui3NFo for 3,6-dideoxy-3-formamidoglucose. The O40-antigen was found to be structurally and serologically related to the O-antigens of P. alcalifaciens O5 and Providencia stuartii O18. The O40-antigen gene cluster between cpxA and yibK was sequenced, and the gene functions were predicted in silico. In agreement with the O-polysaccharide structure established, the genes for the synthesis of dTDP-D-Qui3NFo, UDP-D-Gal, UDP-D-GlcA, and UDP-D-GalNAc as well as those encoding three glycosyltransferases, flippase (Wzx), and O-antigen polymerase (Wzy) were recognized. In addition, homologues of wza, wzb, and wzc genes, which are required for the surface expression of capsular polysaccharides, were found within the gene cluster, suggesting that the O-polysaccharide studied is a part of the capsule-related form of the lipopolysaccharide called K(LPS).

Structure of the O-polysaccharide of Providencia alcalifaciens O35 containing an N-[(S)-1-carboxyethyl]-L-alanine (alanopine) derivative of 4-amino-4,6-dideoxyglucose

The O-polysaccharide of Providencia alcalifaciens O35 was studied by sugar and methylation analyses along with (1)H and (13)C NMR spectroscopy, including 2D (1)H,(13)C HMBC, and NOESY experiments in D2O and, to detect correlations for NH protons, in a 9:1 H2O/D2O mixture. A unique N-(1-carboxyethyl)alanine (alanopine, Alo) derivative of 4-amino-4,6-dideoxyglucose (Qui4N) was identified as the polysaccharide component. Alanopine was isolated by solvolysis of the polysaccharide with triflic acid followed by acid hydrolysis, and its (2S,4S)-configuration was determined by the specific optical rotation. The following structure of the O-polysaccharide was established (the d configuration of Qui4N was ascribed tentatively): [structure: see text].

Lipopolysaccharide core structures and their correlation with genetic groupings of Shigella strains. A novel core variant in Shigella boydii type 16

Bacteria Shigella, the cause of shigellosis, evolved from the intestinal bacteria Escherichia coli. Based on structurally diverse O-specific polysaccharide chains of the lipopolysaccharides (LPSs; O-antigens), three from four Shigella species are subdivided into multiple serotypes. The central oligosaccharide of the LPS called core is usually conserved within genus but five core types called R1-R4 and K-12 have been recognized in E. coli. Structural data on the Shigella core are limited to S. sonnei, S. flexneri and one S. dysenteriae strain, which all share E. coli core types. In this work, we elucidated the core structure in 14 reference strains of S. dysenteriae and S. boydii. Core oligosaccharides were obtained by mild acid hydrolysis of the LPSs and studied using sugar analysis, high-resolution mass spectrometry and two-dimensional NMR spectroscopy. The R1, R3 and R4 E. coli core types were identified in 8, 3 and 2 Shigella strains, respectively. A novel core variant found in S. boydii type 16 differs from the R3 core in the lack of GlcNAc and the presence of a D-glycero-D-manno-heptose disaccharide extension. In addition, the structure of an oligosaccharide consisting of the core and one O-antigen repeat was determined in S. dysenteriae type 8. A clear correlation of the core type was observed with genetic grouping of Shigella strains but not with their traditional division to four species. This finding supports a notion on the existing Shigella species as invalid taxa and a suggestion of multiple independent origins of Shigella from E. coli clones.

The diversity of the core oligosaccharide in lipopolysaccharides

Bacterial lipopolysaccharides (LPSs) are the major component of the outer membrane of Gram-negative bacteria. They have a structural role since they contribute to the cellular rigidity by increasing the strength of cell wall and mediating contacts with the external environment that can induce structural changes to allow life in different conditions. Furthermore, the low permeability of the outer membrane acts as a barrier to protect bacteria from host-derived antimicrobial compounds. Lipopolysaccharides are amphiphilic macromolecules generally comprising three defined regions distinguished by their genetics, structures and function: the lipid A, the core oligosaccharide and a polysaccharide portion, the O-chain. In some Gram-negative bacteria LPS can terminate with the core portion to form rough type LPS (R-LPS, LOS). The core oligosaccharide is an often branched and phosphorylated heterooligosaccharide with less than fifteen sugars, more conserved in the inner region, proximal to the lipid A, and often carrying non-stoichiometric substitutions leading to variation and micro-heterogeneity. The core oligosaccharide contributes to the bacterial viability and stability of the outer membrane, can assure the serological specificity and possesses antigenic properties.