Conjugative pilus tip structure reveals convergence in secretion systems

High-resolution structure of the R388 type IV secretion conjugative pilus tip shows VirB6 at the apex as a dynamic gate, alongside VirB2/VirB5 and KikA.

• Why it matters: Direct-contact secretion systems must link recipient-cell engagement to opening a secretion channel, but the coupling mechanism at the pilus tip has been unresolved.
• What they did: The study determined the first high-resolution structure of the R388 conjugative pilus tip, identifying VirB2 and VirB5 plus unexpected distal components VirB6 and KikA.
• The result: The architecture unifies pilus biogenesis, entry exclusion, and recipient engagement, implying VirB6 gatekeeping couples tip contact to channel opening and KikA shapes distal adhesion.

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