Fusobacterium nucleatum is a principal biofilm-forming bacteria in the human oral microbiome that has been reported to play crucial roles in periodontitis as well as colorectal cancer. Among the diverse range of outer membrane proteins deployed by this bacterium, the RadD adhesin belonging to the Type Va autotransporter secretion system acts as a major component in mediating polymicrobial co-aggregation as well as host-pathogen interactions. While it is well-known that the interactions of RadD could be controlled by exploiting its arginine-inhibitable and lysine-inhibitable properties, the molecular details of those interactions occurring at the receptor-ligand interface remain largely unclear due to the lack of any structural evidence. Here in our study, the RadD adhesin was purified from a Fusobacterium nucleatum subsp. nucleatum strain, which was further used to determine its high-resolution structure using single particle cryo-electron microscopy. To our knowledge, this is the largest monomeric structure solved to date and the first full-length structure of a classical Type Va autotransporter adhesin. The RadD structure reported here revealed a highly flexible beta-barrel translocating unit that was connected by a short linker segment to the extracellular passenger domain with a beta-solenoid super-secondary structure, that had right-handed twists in the central stalk. Although the C-terminal transmembrane domain was flexible and the N-terminal passenger domain possessed directional heterogeneity towards the tip, the focused refinements performed for the shorter segments of the adhesin yielded higher resolutions for the individual domains. Our structure could be used to design potential target-based drugs for periodontitis and colorectal cancer.