Molecular characterization of PcpA: a novel choline-binding protein of Streptococcus pneumoniae.

The gene pcpA that encodes a novel pneumococcal choline-binding protein has been cloned and characterized. Northern blot analysis revealed that pcpA is expressed during the exponential phase of growth of pneumococci as a monocistronic transcript of about 2.3 kb. The transcription start site has been located 132 bp upstream of the start codon and the proposed -35 and -10 boxes that are highly similar to those of the typical sigma 70 promoters from Escherichia coli. This gene encodes a putative 79 kDa protein that contains a typical C-terminal choline-binding domain (ChBD). The ChBD of PcpA is built up by 11 identical motifs of 20 amino acids plus a tail of 19 amino acids, which represents the longest ChBD that has been characterized so far. Interestingly, two tandem arrays of five characteristic amphipathic leucine reach repeats (LRRs) of 22-26 amino acids in length have been found in the N-terminal region of PcpA. Since LRRs have been proposed to be involved in protein-protein and protein-lipid interactions our findings suggests a role for PcpA in pneumococcal adhesion.