Project Summary Fusobacterium nucleatum (Fn) is a Gram-negative oral commensal that is quickly attracting attention of the medical and research community. It is an opportunistic pathogen implicated in periodontal disease as well as in infections at numerous extra-oral sites, including adverse pregnancy outcomes and colorectal cancer. FadA is a novel adhesin and key virulence factor from Fn. It is required from Fn to bind and invade epithelial and endothelial cells and to colonize the placenta and colorectal carcinoma. FadA binds to VE-cadherin on endothelial cells and E-cadherin on epithelial and colorectal cancer cells, inducing varying responses from different host cells. Our recent study reveals that FadA is differentially regulated and secreted. The secreted FadA exhibits amyloid-like properties and correlates with increased virulence. As Fn is considered a primarily commensal organism, the question arises how it switches from a commensal to a pathogen. Our central hypothesis is that the commensal and pathogenic states are determined through regulation of FadA. In this application, we propose to characterize the amyloid-like properties of FadA, identify components involved in its secretion, and determine its role in biofilm formation and periodontal infection. This study is highly significant because it characterizes a novel and critical virulence component from a pathogen involved in multiple debilitating human diseases. Results from our study will identify therapeutic targets for prevention and treatment of a series of human diseases within and beyond the oral cavity.