Identification of the teichoic acid phosphorylcholine esterase in Streptococcus pneumoniae

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 phosphorylc holine residues which serve as anchors for surface-located choline-binding proteins and are also recognized by components of the host response, such a s the human C-reactive protein, a class of myeloma proteins and PAF recepto rs. In the present study, we describe the identification of the pneumococca l pce gene encoding for a teichoic acid phosphorylcholine esterase (Pce), a n enzymatic activity capable of removing phosphorylcholine residues from th e cell wall teichoic acid and lipoteichoic acid. Pce carries an N-terminal signal sequence, contains a C-terminal choline-binding domain with 10 homol ogous repeating units similar to those found in other pneumococcal surface proteins, and the catalytic (phosphorylcholine esterase) activity is locali zed on the N-terminal part of the protein. The mature protein was overexpre ssed in Escherichia coli and purified in a one-step procedure by choline-af finity chromatography and the enzymatic activity was followed using the chr omophoric p-nitrophenyl-phosphorylcholine as a model substrate. The product of the enzymatic digestion of H-3-choline-labelled cell walls was shown to be phosphorylcholine. Inactivation of the pce gene in S. pneumoniae strain s by insertion-duplication mutagenesis caused a unique change in colony mor phology and a striking increase in virulence in the intraperitoneal mouse m odel. Pce may be a regulatory element involved with the interaction of S. p neumoniae with its human host.