The product of the pilQ gene is essential for the biogenesis of type IV pili in Neisseria gonorrhoeae

Abstract

The product of the Neisseria gonorrhoeae omc gene possesses regions homologous to those found in members of a protein superfamily that are associated with the translocation of proteins and DNA-protein complexes across the outer membrane. Amongst its protein homologues, Omc has higher overall homology to PilQ, which is required for type IV pilus expression in Pseudomonas aeruginosa, and OrfE, which is required for sequence-specific DNA uptake by Haemophilus influenzae. The function of Omc, however, is unknown and gonococcal omc mutants have not been described. We constructed gonococcal mutants expressing truncated forms of the protein, and found that these mutants are severely defective for both pilus expression and competence for natural transformation. To be consistent with pre-existing pilus gene nomenclature, we have redesignated the gene pilQ instead of omc, and its product, PilQ instead of Omc. The MS11 gene was sequenced and found to differ from the DNA sequence reported for that of another gonococcal strain; these differences were associated with a repeated DNA element, suggesting a genetic basis for structural variation in PilQ. The results also show that PilQ- mutants are distinct from previously described gonococcal pilus-assembly mutants and P. aeruginosa PilQ- mutants by virtue of their expression of rare pilus filaments. Taking these data into account, PilQ is proposed to function in the terminal steps of organelle biogenesis by acting as a pilus channel or pore.

Structure and function of repetitive sequence elements associated with a highly polymorphic domain of the Neisseria meningitidis PilQ protein

“…Most striking perhaps is the variability in the number of tandem repeats of the sequence PAKQQAAA (and minor variants thereof), which varies from four to seven copies. Although the sequences for only two Gc pilQ genes are currently available, PCR-based studies analogous to those detailed here using a large number of Gc isolates indicate that these strains carry either two or three copies of the SBR (S. Drake and M. Koomey, unpublished), as found previously for strains 2686 and MS11 respectively (Drake and Koomey, 1995). It appears that the presence of four or more SBRs is unique to Mc, with the majority of strains (17 out of 22) possessing five or six SBRs.…”

Topology of the outer-membrane secretin PilQ from Neisseria meningitidis

“…Impaired stability of secretins has previously been observed in XcpQ (Bitter et al, 1998), PulD (Guilvout et al, 1999) and neisserial PilQ mutants (Drake & Koomey, 1995;Tønjum et al, 1998;Zhao et al, 2005). The meningococcal PilQ complex forms a homo-dodecamer (Collins et al, 2001) The identification of the location of the SBR region, by determination of the structure of the Mc-205 variant of PilQ in complex with Ni-NTA nanogold, showed a central position within the 'arms' region of the complex (Collins et al, 2004).…”

Kinetics of DNA uptake during transformation provide evidence for a translocation ratchet mechanism

“…In the outer membrane PilQ proteins form the secretin pore for the pilus (17). Both proteins are essential for DNA uptake (17). The secretin assembly has DNA-binding properties and is part of a complex that spans the outer and inner membranes (18,19).…”

“…They include the major pilin subunit (PilE) that polymerizes to form pili (16). In the outer membrane PilQ proteins form the secretin pore for the pilus (17). Both proteins are essential for DNA uptake (17).…”