Biology subjects

Widmalm, G.

Publications and source records attributed to Widmalm, G..

5 recordsLinked to original sources

bioRxiv2025

A conserved glycan motif overcomes antigenic variation inducing broadly reactive antibodies against the zoonotic pathogen Streptococcus suis

Streptococcus suis is a largely neglected but emerging bacterial zoonotic pathogen of global concern for animal welfare, antibiotic resistance development and human health. No effective vaccines are currently available. Here, we identified and characterized the function and structure of two cell wall polysaccharide variants in pathogenic S. suis strains using genetic deletion and (heterologous) complementation, lectin staining, glycan composition analysis and specialized NMR spectroscopy. Both glycan variants were anionic polymers that differed in the presence of glucose in the side-chain as a result of allelic variation in a glycosyltransferase gene. Deletion of this variable glycosyltransferase revealed an identical glycan core and affected S. suis morphology and lysozyme resistance. Immunization of pigs with this core domain induced antibodies recognizing a wide range of antigenically-diverse pathogenic S. suis strains. This study provides new insights for developing next-generation glycoconjugate vaccines, whereby a single-glycan target could protect against the emerging zoonotic pathogen S. suis.

microbiology↗

bioRxiv2024

Structure and mechanism of biosynthesis of Streptococcus mutans cell wall polysaccharide

Streptococcus mutans, the causative agent of human dental caries, expresses a cell wall attached Serotype c-specific Carbohydrate (SCC) that is critical for cell viability. SCC consists of a repeating [->]3)-Rha(1[->]2)-Rha(1[->] polyrhamnose backbone, with glucose (Glc) side-chains and glycerol phosphate (GroP) decorations. This study reveals that SCC has one major and two minor Glc modifications. The major Glc modification, -Glc, attached to position 2 of 3-rhamnose, is installed by SccN and SccM glycosyltransferases and is the site of the GroP addition. The minor Glc modifications are {beta}-Glc linked to position 4 of 3-rhamnose installed by SccP and SccQ glycosyltransferases, and -Glc attached to position 4 of 2-rhamnose installed by SccN working in tandem with an unknown enzyme. Both the major and the minor {beta}-Glc modifications control bacterial morphology, but only the GroP and major Glc modifications are critical for biofilm formation.

microbiology↗

bioRxiv2024

A platform for the recombinant production of Group A Streptococcus glycoconjugate vaccines

Strep A is a human-exclusive bacterial pathogen killing annually more than 500,000 patients, and no current licensed vaccine exists. Strep A bacteria are highly diverse, but all produce an essential, abundant, and conserved surface carbohydrate, the Group A Carbohydrate, which contains a rhamnose polysaccharide (RhaPS) backbone. RhaPS is a validated universal vaccine candidate in a glycoconjugate prepared by chemical conjugation of the native carbohydrate to a carrier protein. We engineered the Group A Carbohydratte biosynthesis pathway to enable recombinant production using the industry standard route to couple RhaPS to selected carrier proteins within E. coli cells. The structural integrity of the produced recombinant glycoconjugate vaccines was confirmed by NMR spectroscopy and mass spectrometry. Purified RhaPS glycoconjugates elicited carbohydrate-specific antibodies in mice and rabbits and bound to the surface of multiple Strep A strains of diverse M-types, confirming the recombinantly produced RhaPS glycoconjugates as valuable vaccine candidates.

microbiology↗

bioRxiv2021

PplD is a de-N-acetylase of the cell wall linkage unit of streptococcal rhamnopolysaccharides

The cell wall of the human bacterial pathogen Group A Streptococcus (GAS) consists of peptidoglycan decorated with the Lancefield group A carbohydrate (GAC). GAC is a promising target for the development of GAS vaccines. In this study, employing chemical, compositional, and NMR methods, we show that GAC is attached to peptidoglycan via glucosamine 1-phosphate. This structural feature makes the GAC-peptidoglycan linkage highly sensitive to cleavage by nitrous acid and resistant to mild acid conditions. Using this characteristic of the GAS cell wall, we identify PplD as a protein required for deacetylation of linkage N-acetylglucosamine (GlcNAc). X-ray structural analysis indicates that PplD performs catalysis via a modified acid/base mechanism. Genetic surveys in silico together with functional analysis indicate that PplD homologs deacetylate the polysaccharide linkage in many streptococcal species. We further demonstrate that introduction of positive charges to the cell wall by GlcNAc deacetylation protects GAS against host cationic antimicrobial proteins.

microbiology↗

bioRxiv2018

Genetic insight into zinc and antimicrobial toxicity uncovers a glycerol phosphate modification on streptococcal rhamnose polysaccharides

Cell wall glycopolymers on the surface of Gram-positive bacteria are fundamental to bacterial physiology and infection biology. These structures have also gained interest as vaccine antigens, in particular for the human pathogens Group A Streptococcus (GAS) and Streptococcus mutans. Streptococcal cell wall glycopolymers are considered to be functional homologues of wall teichoic acids but surprisingly lack the biologically-relevant and characteristic anionic charge. Here we identify gacH, a gene of unknown function in the GAS Group A Carbohydrate (GAC) biosynthetic cluster, in two independent transposon library screens for its ability to confer resistance to zinc and susceptibility to the bactericidal enzyme human group IIA secreted phospholipase A2. To understand the underlying mechanism of these phenotypes, we determined the structure of the extracellular domain of GacH and discover that it represents a new family of glycerol phosphate (GroP) transferases. Importantly, we demonstrate the presence of GroP in both the GAC and the homologous Serotype c Carbohydrate (SCC) from S. mutans, which is conferred by gacH and sccH products, respectively. NMR analysis of GAC released from cell wall by non-destructive methods reveals that approximately 30% of the GAC GlcNAc side-chains are modified by GroP at the C6 hydroxyl group. This previously unrecognized structural modification impacts host-pathogen interaction and has implications for vaccine design. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/337519v4_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@6d7598org.highwire.dtl.DTLVardef@435695org.highwire.dtl.DTLVardef@e9515corg.highwire.dtl.DTLVardef@1dc78b7_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗