Structural and functional examination of Neisseria gonorrhoeae TfpC reveals a dynamic two-domain architecture required for type IV pilus function

The Neisseria gonorrhoeae (Gc) Type IV pilus (T4p) is a critical apparatus for colonization and virulence. This molecular machine resides at the host-pathogen interface and mediates adherence to host cells, twitching motility, natural transformation, and resistance to oxidative agents. Previously, we identified a DUF4124 family, T4p component, TfpC. TfpC is required for full T4p elaboration, and deleting the tfpC gene reduced natural transformation competence and resulted in an under-piliated colony morphology. Our earlier models suggested TfpC is composed of an N-terminal transmembrane helix and a proline-rich disordered region followed by a C-terminal coiled-coil. Here, we used targeted structural and genetic approaches to define TfpC's molecular structure. Our new data show that TfpC's N-terminal domain forms a novel, dynamic three-stranded β-sheet structure. These data indicate that the flexible disordered region acts as a linker between the N- and C-terminal domains. Functionally, we illustrate TfpC requires an acidic face within the C-terminal coiled-coil domain to mediate pilus biogenesis and function. This study characterizes a unique protein fold and family and defines the contributions of TfpC's domains to its function.