Pneumococcal VncR Strain-Specifically Regulates Capsule Polysaccharide Synthesis

Abstract

Capsular polysaccharides (CPS), a major virulence factor in Streptococcus pneumoniae, become thicker during blood invasion while not during asymptomatic nasopharyngeal colonization. However, the underlying mechanism controlling this differential pneumococcal CPS regulation remain unclear. Here, we show how VncR, the response regulator of the vancomycin resistance locus (vncRS operon), regulates CPS expression in vncR mutants in three serotype (type 2, 3, and 6B) backgrounds upon exposure to serum lactoferrin (LF). Comparative analysis of CPS levels in the wild type (WT) of three strains and their isogenic vncR mutants after LF exposure revealed a strain-specific alteration in CPS production. Consistently, VncR-mediated strain-specific CPS production is correlated with pneumococcal virulence, in vivo. Electrophoretic mobility-shift assay and co-immunoprecipitation revealed an interaction between VncR and the cps promoter (cpsp) in the presence of serum. In addition, in silico analysis uncovered this protein-DNA interaction, suggesting that VncR binds with the cpsp, and recognizes the strain-specific significance of the tandem repeats in cpsp. Taken together, the interaction of VncR and cpsp after serum exposure plays an essential role in regulating differential strain-specific CPS production, which subsequently determines strain-specific systemic virulence. This study highlights how host protein LF contributes to pneumococcal VncR-mediated CPS production. As CPS plays a significant role in immune evasion, these findings suggest that drugs designed to interrupt the VncR-mediated CPS production could help to combat pneumococcal infections.

StkP- and PhpP-Mediated Posttranslational Modifications Modulate the S. pneumoniae Metabolism, Polysaccharide Capsule, and Virulence

“…Such cross-phosphorylation phenomena are reported in Gram-positive bacteria such as Bacillus subtilis ( 94 – 96 ) and S. pyogenes ( 64 , 97 ). Recently, pneumococcal VncR has been reported to regulate capsule polysaccharide synthesis, although in a strain-specific manner ( 52 ). VncR is the response regulator of the vancomycin resistance locus ( vncRS operon or rr10/spd_0524/0525 ).…”

“…The RUP region contains the “cre” binding site, and based on which, we predicted the role of the StkP-phosphorylated CcpA in the repression of the genes. As described above, VncR protein also binds the 218-bp P cps , but only in the presence of serum in a type-specific manner ( 52 ), and positively regulates the expression of cps2 genes. It is unknown whether StkP phosphorylates VncR and modulates the VncR-mediated cps2 gene expression.…”

“…The cps promoter (P cps ) regulates the transcription of cps genes. Predicted in silico bioinformatic analysis ( 50 ), direct Pcps -binding studies ( 51 ), and recent findings on VncR ( 52 ) have shown that several candidate regulators control transcription of the cps locus genes. These include CcpA, a GntR family transcriptional regulator SPD_0064, a MarR family transcriptional regulator SPD_0379, DNA-binding protein HU, CodY, GlnR, and RitR ( 51 ).…”

Crystal Structure of the Pneumococcal Vancomycin-Resistance Response Regulator DNA-Binding Domain

“…Thus, PhoB and VncR might bind to different target DNA. Recently, we investigated VncR directly binds to pneumococcal capsular polysaccharide locus (Ghosh et al, 2019). Thus, our VncRc structure and DNA binding model will give insights into the transcriptional regulation of CPS biosynthesis-related genes.…”