ISOLATION AND CHARACTERIZATION OF FAP1, A FIMBRIAE-ASSOCIATED ADHESINOF STREPTOCOCCUS-PARASANGUIS FW213

An adhesin of Streptococcus parasanguis FW213, a primary colonizer of the tooth surface, has been purified from the culture medium by immuno affinity chromatography. The purified protein has a molecular mass of 200 kDa and stains positively for carbohydrate. The amino-terminal seq uence indicated that this protein represented a unique streptococcal s urface protein. Immunogold labelling of the bacterium indicated that t his protein was associated with fimbriae and designated Fap1 (fimbriae -associated protein). A polymerase chain reaction (PCR) product based on the amino terminus of Fap1 was used to probe an FW213 genomic libra ry. A 9 kb fragment containing the fap1 gene was isolated and 2.5 kb h ave been sequenced. Generation of fap1 mutants by a single cross-over (Campbell insertion) or a non-polar allelic exchange abolished the exp ression of Fap1. The inactivation of fap1 resulted in a dramatic reduc tion in the expression of the long peritrichous fimbriae and adhesion to saliva-coated hydroxylapatite (SHA). Northern blots probed with an internal gene fragment of fap1 hybridized to a 9 kb transcript, which suggests that fap1 is transcribed as a polycistronic message. These da ta demonstrate that Fap1 is a unique streptococcal adhesin that is inv olved in the assembly of S. parasanguis FW213 fimbriae and adhesion to SHA.