Identification of the teichoic acid phosphorylcholine esterase in Streptococcus pneumoniae

Abstract

Streptococcus pneumoniae is a major human pathogen and many interactions of this bacterium with its host appear to be mediated, directly or indirectly, by components of the bacterial cell wall, specifically by the phosphorylcholine residues which serve as anchors for surface‐located choline‐binding proteins and are also recognized by components of the host response, such as the human C‐reactive protein, a class of myeloma proteins and PAF receptors. In the present study, we describe the identification of the pneumococcal pce gene encoding for a teichoic acid phosphorylcholine esterase (Pce), an enzymatic activity capable of removing phosphorylcholine residues from the cell wall teichoic acid and lipoteichoic acid. Pce carries an N‐terminal signal sequence, contains a C‐terminal choline‐binding domain with 10 homologous repeating units similar to those found in other pneumococcal surface proteins, and the catalytic (phosphorylcholine esterase) activity is localized on the N‐terminal part of the protein. The mature protein was overexpressed in Escherichia coli and purified in a one‐step procedure by choline‐affinity chromatography and the enzymatic activity was followed using the chromophoric p‐nitrophenyl‐phosphorylcholine as a model substrate. The product of the enzymatic digestion of 3H‐choline‐labelled cell walls was shown to be phosphorylcholine. Inactivation of the pce gene in S. pneumoniae strains by insertion‐duplication mutagenesis caused a unique change in colony morphology and a striking increase in virulence in the intraperitoneal mouse model. Pce may be a regulatory element involved with the interaction of S. pneumoniae with its human host.

Versatility of pneumococcal surface proteins

“…The phosphorylcholine esterase activity of the Pce protein (also referred to as CbpE) removes PCho from the cell wall and causes changes in colony phenotype (de las Rivas et al, 2001;Vollmer & Tomasz, 2001). Recently, structural information for the catalytic domain (Garau et al, 2005) Fig.…”

“…The ability of Pce to modify the amount of PCho on the cell wall has been shown to be relevant for pneumococcal adherence to human cells and for nasopharyngeal colonization of rats (Gosink et al, 2000). Strikingly, loss of function has also been shown to increase the virulence of pneumococci when inoculated into the peritoneum of mice (Vollmer & Tomasz, 2001). It is possible that the increased number of choline residues promotes interaction with the PAFr during infection.…”

Bacterial exploitation of phosphorylcholine mimicry suppresses inflammation to promote airway infection

“…Similar to our findings upon deple- significantly different in terms of growth characteristics in vitro (Supplemental Figure 2A), sensitivity to complement deposition (Supplemental Figure 3A), capsule expression levels (Supplemental Figure 3B), or cell surface ChoP accessibility (Supplemental Figure 3C) as assessed by bacterial flow cytometry. Using recombinant Pce esterase (rPce), we next confirmed that the enzyme bears efficient ChoP hydrolysis activity upon incubation with chromogenic substrate p-nitrophenylphosphorylcholine (pNPPC), which yields p-nitrophenol upon removal of its ChoP moiety ( Figure 5C) (56). To assess whether rPce directly inhibits PAF-mediated stimulation of neutrophils, we pretreated PAF at a range of physiologic concentrations centered around 3 nM (the concentration detected by ESI/MS) with rPce enzyme or PBS control.…”

“…The near-universal conservation of Pce among pneumococcal clinical isolates (65) and results from early animal studies (66) support the idea that the enzyme contributes to bacterial fitness during airway infection, but the nature of its function in vivo has been less clear. Most studies characterizing Pce activity have focused on its ability to remodel the pneumococcal cell wall by hydrolyzing ChoP residues from teichoic acid chains, a function associated with enhanced adhesion to epithelial surfaces (49,56). However, Pce-deficient pneumococci exhibit essentially unaltered epithelial adherence properties, and the enzyme is unable to hydrolyze more than 30% of ChoP residues from these substrates, even in saturating conditions (66,67).…”

A novel glucan-binding protein with lipase activity from the oral pathogen Streptococcus mutans

“…One such enzyme is Pce, the teichoic acid phosphorylcholine esterase of S. pneumoniae and S. oralis, which is able to remove phosphorylcholine from cell wall teichoic and LTAs (De las Rivas et al, 2001;Ronda et al, 1991;Vollmer & Tomasz, 2001). S. mutans does not appear to possess a homologue of Pce and there is no sequence homology between the enzymic domains of GbpD and Pce.…”