SEIFERT, H. S. | Search bioRxiv

bioRxiv2026

Restriction-modification systems are required for Neisseria gonorrhoeae pilin antigenic variation

Neisseria gonorrhoeae (Gc) pilin antigenic variation is a diversity-generating system that uses gene conversion to produce a variety of PilE protein variants, the major subunit of the Type IV pilus (T4p). Pilin antigenic variation allows the bacteria to escape immune surveillance and can alter T4p expression. While pilin antigenic variation requires many conserved homologous recombination and DNA repair factors, the pattern of sequence changes leading to pilin antigenic variants resembles that of an annealing reaction, rather than the expected long recombination tracts usually found in homologous recombination. We demonstrate that two paralogous restriction modification modules cleave specific, unmodified sequences within the expressed and silent pilin loci and that cleavage is essential for pilin antigenic variation. Moreover, these restriction activities affect the bacteriums fitness. These findings partially explain the patchwork recombination patterns of pilin antigenic variants and suggest a unique mechanism for generating diversity.

microbiology↗

bioRxiv2020

Discovery of a new Neisseria gonorrhoeae Type IV pilus assembly factor, TfpC

Neisseria gonorrhoeae rely 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 N. gonorrhoeae strain FA1090 as containing a gene encoding a protein required to stabilize the Type IV pilus in its extended, non-retracted conformation. We have named the gene tfpC and the protein TfpC. Deletion of tfpC produces a nonpiliated colony morphology and immuno-transmission electron microscopy confirms that the pili are lost in the {Delta}tfpC mutant, although there is some pilin detected near the bacterial cell surface. A copy of the tfpC gene expressed from a lac promoter restores pilus expression and related phenotypes. A {Delta}tfpC mutant shows reduced levels of pilin protein, but complementation with a tfpC gene restored pilin to normal levels. Bioinformatic searches show there are orthologues in numerous bacteria species but not all Type IV pilin expressing bacteria contain orthologous genes. Co-evolution and NMR analysis indicates that TfpC contains an N-terminal transmembrane helix, a substantial extended/unstructured region and a highly charge C-terminal coiled-coil domain. ImportanceMost bacterial species express one or more extracellular organelles called pili/fimbriae that are required for many properties of each bacterial cell. The Neisseria gonorrhoeae Type IV pilus is a major virulence and colonization factor for the sexually transmitted infection, gonorrhea. We have discovered a new protein of Neisseria gonorrhoeae called TfpC that is required to maintain the Type IV pili on the bacterial cell surface. There are similar proteins found in the other members of the Neisseria genus and many other bacterial species important for human health.

microbiology↗