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Automated glycan assembly of Streptococcus pneumoniae type 14 capsular polysaccharide fragments.

ABSTRACT: S. pneumoniae is a major human pathogen with increasing antibiotic resistance. Pneumococcal vaccines consist of capsular polysaccharide (CPS) or their related fragments conjugated to a carrier protein. The repeating unit of S. pneumoniae type 14 CPS shares a core structure with the CPS of Group B Streptococcus (GBS) type III: the only difference is that the latter exhibits a sialic acid unit, with a α-2,3 linkage to galactose. Here, the automated glycan assembly (AGA) of two frameshifts of the repeating unit of S. pneumoniae type 14 is described. The same strategy is used to assemble dimers of the different repeating unit frameshifts. The four structures are assembled with only three commercially available monosaccharide building blocks. We also report an example of how enzymatic sialylation of the compounds obtained with AGA completes a synthetic route for GBS type III glycans. The synthesized structures were tested in competitive ELISA and further confirmed the branched tetrasaccharide Gal-Glc-(Gal-)GlcNAc to be the minimal epitope of S. pneumoniae type 14.

SUBMITTER: Loucano J

PROVIDER: S-EPMC9054924 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Automated glycan assembly of Streptococcus pneumoniae type 14 capsular polysaccharide fragments.

Louçano João J Both Peter P Marchesi Andrea A Del Bino Linda L Adamo Roberto R Flitsch Sabine S Salwiczek Mario M

RSC advances 20200622 40

S. pneumoniae is a major human pathogen with increasing antibiotic resistance. Pneumococcal vaccines consist of capsular polysaccharide (CPS) or their related fragments conjugated to a carrier protein. The repeating unit of S. pneumoniae type 14 CPS shares a core structure with the CPS of Group B Streptococcus (GBS) type III: the only difference is that the latter exhibits a sialic acid unit, with a α-2,3 linkage to galactose. Here, the automated glycan assembly (AGA) of two ...[more]

PMID: 35517348

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Project description:UnlabelledThe use of pneumococcal capsular polysaccharide (PPS)-based vaccines has resulted in a substantial reduction in invasive pneumococcal disease. However, much remains to be learned about vaccine-mediated immunity, as seven-valent PPS-protein conjugate vaccine use in children has been associated with nonvaccine serotype replacement and 23-valent vaccine use in adults has not prevented pneumococcal pneumonia. In this report, we demonstrate that certain PPS-specific monoclonal antibodies (MAbs) enhance the transformation frequency of two different Streptococcus pneumoniae serotypes. This phenomenon was mediated by PPS-specific MAbs that agglutinate but do not promote opsonic effector cell killing of the homologous serotype in vitro. Compared to the autoinducer, competence-stimulating peptide (CSP) alone, transcriptional profiling of pneumococcal gene expression after incubation with CSP and one such MAb to the PPS of serotype 3 revealed changes in the expression of competence (com)-related and bacteriocin-like peptide (blp) genes involved in pneumococcal quorum sensing. This MAb was also found to induce a nearly 2-fold increase in CSP2-mediated bacterial killing or fratricide. These observations reveal a novel, direct effect of PPS-binding MAbs on pneumococcal biology that has important implications for antibody immunity to pneumococcus in the pneumococcal vaccine era. Taken together, our data suggest heretofore unsuspected mechanisms by which PPS-specific antibodies could affect genetic exchange and bacterial viability in the absence of host cells.ImportanceCurrent thought holds that pneumococcal capsular polysaccharide (PPS)-binding antibodies protect against pneumococcus by inducing effector cell opsonic killing of the homologous serotype. While such antibodies are an important part of how pneumococcal vaccines protect against pneumococcal disease, PPS-specific antibodies that do not exhibit this activity but are highly protective against pneumococcus in mice have been identified. This article examines the effect of nonopsonic PPS-specific monoclonal antibodies (MAbs) on the biology of Streptococcus pneumoniae. The results showed that in the presence of a competence-stimulating peptide (CSP), such MAbs increase the frequency of pneumococcal transformation. Further studies with one such MAb showed that it altered the expression of genes involved in quorum sensing and increased competence-induced killing or fratricide. These findings reveal a novel, previously unsuspected mechanism by which certain PPS-specific antibodies exert a direct effect on pneumococcal biology that has broad implications for bacterial clearance, genetic exchange, and antibody immunity to pneumococcus.

Project description:Expression of a capsular polysaccharide is considered a hallmark of most invasive species of bacteria, including Streptococcus pneumoniae, in which the capsule is among the principal virulence factors and is the basis for successful vaccines. Consequently, it was previously assumed that capsule production distinguishes S. pneumoniae from closely related commensals of the mitis group streptococci. Based on antigenic and genetic analyses of 187 mitis group streptococci, including 90 recognized serotypes of S. pneumoniae, we demonstrated capsule production by the Wzy/Wzx pathway in 74% of 66 S. mitis strains and in virtually all tested strains of S. oralis (subspecies oralis, dentisani, and tigurinus) and S. infantis Additional analyses of genomes of S. cristatus, S. parasanguinis, S. australis, S. sanguinis, S. gordonii, S. anginosus, S. intermedius, and S. constellatus revealed complete capsular biosynthesis (cps) loci in all strains tested. Truncated cps loci were detected in three strains of S. pseudopneumoniae, in 26% of S. mitis strains, and in a single S. oralis strain. The level of sequence identities of cps locus genes confirmed that the structural polymorphism of capsular polysaccharides in S. pneumoniae evolved by import of cps fragments from commensal Streptococcus species, resulting in a mosaic of genes of different origins. The demonstrated antigenic identity of at least eight of the numerous capsular polysaccharide structures expressed by commensal streptococci with recognized serotypes of S. pneumoniae raises concerns about potential misidentifications in addition to important questions concerning the consequences for vaccination and host-parasite relationships both for the commensals and for the pathogen. Expression of a capsular polysaccharide is among the principal virulence factors of Streptococcus pneumoniae and is the basis for successful vaccines against infections caused by this important pathogen. Contrasting with previous assumptions, this study showed that expression of capsular polysaccharides by the same genetic mechanisms is a general property of closely related species of streptococci that form a significant part of our commensal microbiota. The demonstrated antigenic identity of many capsular polysaccharides expressed by commensal streptococci and S. pneumoniae raises important questions concerning the consequences for vaccination and host-parasite relationships both for the commensals and the pathogen.

Dataset Information

Automated glycan assembly of Streptococcus pneumoniae type 14 capsular polysaccharide fragments.

Publications

Automated glycan assembly of <i>Streptococcus pneumoniae</i> type 14 capsular polysaccharide fragments.

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