Isolation and characterization of Fap1, a fimbriae‐associated adhesin ofStreptococcus parasanguisFW213

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Abstract
An adhesin ofStreptococcus parasanguisFW213, a primary colonizer of the tooth surface, has been purified from the culture medium by immunoaffinity chromatography. The purified protein has a molecular mass of 200 kDa and stains positively for carbohydrate. The amino‐terminal sequence indicated that this protein represented a unique streptococcal surface protein. Immunogold labelling of the bacterium indicated that this 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 library. A 9 kb fragment containing thefap1gene was isolated and 2.5 kb have been sequenced. Generation offap1mutants by a single cross‐over (Campbell insertion) or a non‐polar allelic exchange abolished the expression of Fap1. The inactivation offap1resulted in a dramatic reduction in the expression of the long peritrichous fimbriae and adhesion to saliva‐coated hydroxylapatite (SHA). Northern blots probed with an internal gene fragment offap1hybridized to a 9 kb transcript, which suggests thatfap1is transcribed as a polycistronic message. These data demonstrate that Fap1 is a unique streptococcal adhesin that is involved in the assembly ofS.parasanguisFW213 fimbriae and adhesion to SHA.