Glycosyltransferases within the psrP Locus Facilitate Pneumococcal Virulence

Abstract

The Pneumococcal Serine-Rich Repeat Protein (PsrP) is a high-molecular weight, glycosylated adhesin that promotes the attachment of Streptococcus pneumoniae (Spn) to host cells. PsrP, its associated glycosyltransferases, and dedicated secretion machinery, are encoded in a 37 kb genomic island that is present in many invasive clinical isolates of Spn. PsrP has been implicated in establishment of lung infection in murine models, although specific roles of the PsrP glycans in disease progression or bacterial physiology have not been elucidated. Moreover, enzymatic specificities of associated glycosyltransferases are yet to be fully characterized. We hypothesized that the glycosyltransferases that modify PsrP are critical for the adhesion properties and infectivity of Spn. Here, we characterize the putative Spn psrP-locus glycosyltransferases responsible for PsrP glycosylation. We also begin to elucidate their roles in Spn virulence. We show that four glycosyltransferases within the psrP locus are indispensable for Spn biofilm formation, lung epithelial cell adherence, and establishment of lung infection in a mouse model of pneumococcal pneumonia. IMPORTANCE PsrP has previously been identified as a necessary virulence factor for many serotypes of Spn and studied as a surface glycoprotein. Thus, studying the effects on virulence of each glycosyltransferase that build the PsrP glycan is of high importance. Our work elucidates the influence of glycosyltransferases (GTs) in vivo. We have identified at least four GTs that are required for lung infection, an indication that it is worthwhile to consider glycosylated PsrP as a candidate for serotype-independent pneumococcal vaccine design.

Pneumococcal genetic variability in age-dependent bacterial carriage

“…The sequence is present in isolates dispersed over the phylogenetic tree and associated with carriage in children ( Figure 2—figure supplement 1 ). This protein is involved in adhesion to epithelial cells and biofilm formation ( Chan et al, 2020 ; Middleton et al, 2021 ; Weiser et al, 2018 ). Given that this sequence lies just upstream of the start codon, it is plausible that variation of this sequence alters the expression of the Sec-dependent adhesin protein, and therefore affects carriage.…”

Pan-genome analysis of Streptococcus suis serotype 2 highlights genes associated with virulence and antibiotic resistance

“…These are associated with the hydrolysis of carbohydrates and the formation of glycosidic bonds (Venegas et al, 2022 ). It plays a crucial role in bacteria's acquisition of external carbon sources, adhesion to host cells, and biofilm formation (Middleton et al, 2021 ; Na et al, 2021 ). In addition, the accessory genome exhibits significantly higher levels of GH compared to the core genome.…”

Prevalence and Homology of the Pneumococcal Serine-Rich Repeat Protein at the Global Scale

“…Furthermore, the discovery of highly mutated forms of the S or SRR1 region gives potential evidence of horizontal gene transfer among isolates and introduces a need for a better understanding of SRRP acquisition and utility. Because the GTs within the PsrP locus are putatively present unanimously when the protein is present, glycans associated with the function and virulence of the protein may represent a more conserved epitope for future vaccine formulations ( 17 ). Glycan portions of glycoconjugate vaccines and viral glycoprotein immunogens not only serve as the antigenic determinant but also contribute to the immunogenicity of these vaccines through eliciting T cell help ( 36 – 41 ).…”

“…Importantly, PsrP extends past the capsule, which may avoid the possibility of capsular shielding of the host immune response during invasive infection ( 15 ). Recently, individual glycosyltransferases (GTs) that putatively act on PsrP were also implicated in the PsrP virulence ( 17 ). Thus, native, glycosylated PsrP has an important role in pneumococcal virulence.…”