The pavA gene of Streptococcus pneumoniae encodes a fibronectin-binding protein that is essential for virulence

Streptococcus pneumoniae colonizes the nasopharynx in up to 40% of healthy subjects, and is a leading cause of middle ear infections (otitis media), m eningitis and pneumonia. Pneumococci adhere to glycosidic receptors on epit helial cells and to immobilized fibronectin, but the bacterial adhesins med iating these reactions are largely uncharacterized. In this report we descr ibe a novel pneumococcal protein PavA, which binds fibronectin and is assoc iated with pneumococcal adhesion and virulence. The pavA gene, present in 6 4 independent isolates of S. pneumoniae tested, encodes a 551 amino acid re sidue polypeptide with 67% identical amino acid sequence to Fbp54 protein i n Streptococcus pyogenes. PavA localized to the pneumococcal cell outer sur face, as demonstrated by immunoelectron microscopy, despite lack of convent ional secretory or cell-surface anchorage signals within the primary sequen ce. Full-length recombinant PavA polypeptide bound to immobilized human fib ronectin in preference to fluid-phase fibronectin, in a heparin-sensitive i nteraction, and blocked binding of wild-type pneumococcal cells to fibronec tin. However, a C-terminally truncated PavA' polypeptide (362 aa residues) failed to bind fibronectin or block pneumococcal cell adhesion. Expression of pavA in Enterococcus faecalis JH2-2 conferred > sixfold increased cell a dhesion levels to fibronectin over control JH2-2 cells. Isogenic mutants of S. pneumoniae, either abrogated in PavA expression or producing a 42 kDa C -terminally truncated protein, showed up to 50% reduced binding to immobili zed fibronectin. Inactivation of pavA had no effects on growth rate, cell m orphology, cell-surface physico-chemical properties, production of pneumoly sin, autolysin, or surface proteins PspA and PsaA. Isogenic pavA mutants of encapsulated S. pneumoniae D39 were approximately 10(4)-fold attenuated in virulence in the mouse sepsis model. These results provide evidence that P avA fibronectin-binding protein plays a direct role in the pathogenesis of pneumococcal infections.