Discovery of a New Neisseria gonorrhoeae Type IV Pilus Assembly Factor, TfpC.

relies on type IV pili (T4p) to promote colonization of their human host and to cause the sexually transmitted infection gonorrhea. This organelle cycles through a process of extension and retraction back into the bacterial cell. Through a genetic screen, we identified the NGO0783 locus of strain FA1090 as containing a gene encoding a protein required to stabilize the type IV pilus in its extended, nonretracted conformation. We have named the gene and the protein TfpC. Deletion of produces a nonpiliated colony morphology, and immuno-transmission electron microscopy confirms that the pili are lost in the Δ mutant, although there is some pilin detected near the bacterial cell surface. A copy of the gene expressed from a promoter restores pilus expression and related phenotypes. A Δ mutant shows reduced levels of pilin protein, but complementation with a gene restored pilin to normal levels. Bioinformatic searches show that there are orthologues in numerous bacterial species, but not all type IV pilin-expressing bacteria contain orthologous genes. Coevolution and nuclear magnetic resonance (NMR) analysis indicates that TfpC contains an N-terminal transmembrane helix, a substantial extended/unstructured region, and a highly charged C-terminal coiled-coil domain. Most bacterial species express one or more extracellular organelles called pili/fimbriae that are required for many properties of each bacterial cell. The type IV pilus is a major virulence and colonization factor for the sexually transmitted infection gonorrhea. We have discovered a new protein of called TfpC that is required to maintain type IV pili on the bacterial cell surface. There are similar proteins found in other members of the genus and many other bacterial species important for human health.