Abstract
Neisseria meningitidis is naturally competent for transformation throughout its growth cycle. Transformation in neisserial species is coupled to the expression of type IV pili, which are present on the cell surface as bundled filamentous appendages, and are assembled, extruded and retracted by the pilus biogenesis components. During the initial phase of the transformation process, binding and uptake of DNA takes place with entry through a presumed outer-membrane channel into the periplasm. This study showed that DNA associates only weakly with purified pili, but binds significantly to the PilQ complex isolated directly from meningococcal membranes. By assessing the DNA-binding activity of the native complex PilQ, as well as recombinant truncated PilQ monomers, it was shown that the N-terminal region of PilQ is involved in the interaction with DNA. It was evident that the binding of ssDNA to PilQ had a higher affinity than the binding of dsDNA. The binding of DNA to PilQ did not, however, depend on the presence of the neisserial DNA-uptake sequence. It is suggested that transforming DNA is introduced into the cell through the outer-membrane channel formed by the PilQ complex, and that DNA uptake occurs by non-specific introduction of DNA coupled to pilus retraction, followed by presentation to DNA-binding component(s), including PilQ.
Highlights
IntroductionNeisseria meningitidis (the meningococcus) is constitutively competent for transformation throughout its growth cycle
Neisseria meningitidis is constitutively competent for transformation throughout its growth cycle
Various concentrations of protein and DNA were tested for binding under several different conditions, and the protein– DNA interaction was monitored using DNA glycosylase MutY as a positive control (Fig. 1a). This analysis showed that assembled N. meningitidis and P. aeruginosa fimbrial structures weakly bound DNA under the conditions employed (Fig. 1b), and that binding could be inhibited by competing DNA- and pilus-specific antibodies (Fig. 1c, d)
Summary
Neisseria meningitidis (the meningococcus) is constitutively competent for transformation throughout its growth cycle. Type IV pili are long fibrous structures emanating from the bacterial surface, and as multifunctional organelles, they are involved in a variety of bacterial processes. In addition to their role in competence, the type IV pili of many species play a role in adherence (Swanson et al, 1971), twitching motility (Bradley, 1974; Mattick, 2002), biofilm formation (O’Toole & Kolter, 1998) and bacteriophage infection (Bradley, 1974).
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