Solution structure of choline binding protein A, the major adhesin of Streptococcus pneumoniae

Abstract

Streptococcus pneumoniae (pneumococcus) remains a significant health threat worldwide, especially to the young and old. While some of the biomolecules involved in pneumococcal pathogenesis are known and understood in mechanistic terms, little is known about the molecular details of bacterium/host interactions. We report here the solution structure of the ‘repeated’ adhesion domains (domains R1 and R2) of the principal pneumococcal adhesin, choline binding protein A (CbpA). Further, we provide insights into the mechanism by which CbpA binds its human receptor, polymeric immunoglobulin receptor (pIgR). The R domains, comprised of 12 imperfect copies of the leucine zipper heptad motif, adopt a unique 3‐α‐helix, raft‐like structure. Each pair of α‐helices is antiparallel and conserved residues in the loop between Helices 1 and 2 exhibit a novel ‘tyrosine fork’ structure that is involved in binding pIgR. This and other structural features that we show are conserved in most pneumococcal strains appear to generally play an important role in bacterial adhesion to pIgR. Interestingly, pneumococcus is the only bacterium known to adhere to and invade human cells by binding to pIgR.

Heterologous expression of pneumococcal virulence factor PspC on the surface of Lactococcus lactis confers adhesive properties

“…In our gene construct, only one R domain for binding with the SC of hpIgR is present and is sufficient to allow adherence and invasion of recombinant lactococci into MDCK-hpIgR cells. This is in agreement with previous studies (surface plasmon resonance analysis) where even more rapid binding was observed when only one R domain is present (Elm et al, 2004;Luo et al, 2005). The gene fusion with the pspC-like hic gene adds the C-terminal part of Hic from aa 266 to 612.…”

“…The generated recombinant plasmid pGKK1 allowed expression of this gene construct under the control of the PnisA promoter. DNA sequencing and the deduced amino acids revealed that the N-terminal part of this modified PspC contains the a-helical domain comprising the Factor H binding domain (Lu et al, 2006;Luo et al, 2005) and one SC-binding domain, designated R domain (Luo et al, 2005), which includes the SC recognition motif RRNYPT (Hammerschmidt et al, 2000). To confirm and detect the recombinant PspC, an immunoblot analysis was performed from soluble protein extracts and with anti-PspC-SH2 antiserum (Fig.…”

Human Antibodies to PhtD, PcpA, and Ply Reduce Adherence to Human Lung Epithelial Cells and Murine Nasopharyngeal Colonization by Streptococcus pneumoniae

“…Other groups have established additional S. pneumoniae proteins involved in adherence to human epithelial cells, such as CbpA (40), PhtD (39), and PsaA (surface protein A) (41). Our study is unique in the design of the adherence assay using human Fabs from natural immunization and purified antigen-specific IgG to evaluate the role of specific antibodies in the S. pneumoniae adherence process.…”

Versatility of pneumococcal surface proteins

“…Structural analysis of R1 (amino acids 175-285) and R2 (amino acids 327-442) of PspC derived from TIGR4 has demonstrated that the R domains adopt an unusual and simple structure composed of three a-helices. Bundling of the helices through a-helixa-helix interactions results in a flat, raft-like structure in which the residues YPT of the minimal SC-binding motif are located in a loop between helix 1 and helix 2 and form a 'tyrosine fork' structure (Luo et al, 2005). PspC molecules are divided into different groups.…”