CONTRIBUTION OF NOVEL CHOLINE-BINDING PROTEINS TO ADHERENCE, COLONIZATION AND IMMUNOGENICITY OF STREPTOCOCCUS-PNEUMONIAE

The surface of Streptococcus pneumoniae is; decorated with a family of choline-binding proteins (CBPs) that are non-covalently bound to the phosphorylcholine of the teichoic acid, Two examples (PspA, a protecti ve antigen, and LytA, the major autolysin) have been well characterize d. We identified additional CPBs and characterized a new CBP, CbpA, as an adhesin and a determinant of virulence, Using choline immobilized on a solid matrix, a mixture of proteins from a pspA-deficient strain of pneumococcus was eluted in a choline-dependent fashion, Antisera to these proteins passively protected mice challenged in the peritoneum with a lethal dose of pneumococci. The predominant component of this m ixture, CbpA, is a 75-kDa surface-exposed protein that reacts with hum an convalescent antisera. The deduced sequence from the corresponding gene showed a chimeric architecture with a unique N-terminal region an d a C-terminal domain consisting of 10 repeated choline-binding domain s nearly identical to PspA. A cbpA-deficient mutant showed a >50% redu ction in adherence to cytokine-activated human cells and failed to bin d to immobilized sialic acid or lacto-N-neotetraose, known pneumococca l ligands on eukaryotic cells, Carriage of this mutant in an animal mo del of nasopharyngeal colonization was reduced 100-fold. There was no difference between the parent strain and this mutant in an intraperito neal model of sepsis. These data for CbpA extend the important functio ns of the CBP family to bacterial adherence and identify a pneumococca l vaccine candidate.