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

Abstract

<i>Neisseria gonorrhoeae</i> 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 <i>N. gonorrhoeae</i> 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 <i>tfpC</i> and the protein TfpC. Deletion of <i>tfpC</i> produces a nonpiliated colony morphology, and immuno-transmission electron microscopy confirms that the pili are lost in the Δ<i>tfpC</i> mutant, although there is some pilin detected near the bacterial cell surface. A copy of the <i>tfpC</i> gene expressed from a <i>lac</i> promoter restores pilus expression and related phenotypes. A Δ<i>tfpC</i> mutant shows reduced levels of pilin protein, but complementation with a <i>tfpC</i> 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.<b>IMPORTANCE</b> Most bacterial species express one or more extracellular organelles called pili/fimbriae that are required for many properties of each bacterial cell. The <i>Neisseria gonorrhoeae</i> type IV pilus is a major virulence and colonization factor for the sexually transmitted infection gonorrhea. We have discovered a new protein of <i>Neisseria gonorrhoeae</i> 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 <i>Neisseria</i> genus and many other bacterial species important for human health.