Characterization of Adhesion FadA of Fusobacterium Nucleatum

Fusobacterium nucleatum is a gram-negative filamentous anaerobe associated with various forms of periodontal diseases. It is a key component of periodontal plaque due to its abundance and its ability to coaggregate with other species in the oral cavity. Our previous study revealed that F. nucleatum adheres to and invades human oral epithelial cells. A 16-KD polypeptide of F. nucleatum, designated as FadA (for Fusobacterium adhesin A), was identified to bind to the biotinylated epithelial-cell KB surface proteins. The fadA gene from F. nucleatum strain 12230 was cloned and sequenced. It is composed of 130 amino acids with the first 18 residues encoding a typical signal peptide sequence, absent in the mature protein. Objectives: The purpose of this study is to investigate the role of FadA in adherence. Methods: A FadA-His tag fusion protein was constructed, expressed in E. coli BL21(DE3), and purified to homogeneity. The adhesion property of the recombinant FadA was then tested using in vitro tissue culture attachment and inter-bacterial coaggregation assays. Results: The fadA-expressing BL21(DE3) exhibited as much as a 10-fold increase in adherence to epithelial cells as compared to the non-fadA-expressing strain. Furthermore, it coaggregated with several oral bacteria, including Porphyromonas gingivalis, while the non-fadA-expressing strain did not. Conclusion: FadA is a novel adhesin likely involved in binding to different targets. Funded in part by NIH grants DE07034 and DE08293, and CWRU School of Dentistry Research Start-up Fund.