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Abstract:
Type IVa pili are ubiquitous and versatile bacterial cell surface
filaments that undergo cycles of extension, adhesion and retraction
powered by the cell-envelope spanning type IVa pilus machine (T4aPM).
The overall architecture of the T4aPM and the location of 10 conserved
core proteins within this architecture have been elucidated. Here, using
genetics, cell biology, proteomics and cryo-electron tomography, we
demonstrate that the PilY1 protein and four minor pilins, which are
widely conserved in T4aP systems, are essential for pilus extension in
Myxococcus xanthus and form a complex that is an integral part of the
T4aPM. Moreover, these proteins are part of the extended pilus. Our data
support a model whereby the PilY1/minor pilin complex functions as a
priming complex in T4aPM for pilus extension, a tip complex in the
extended pilus for adhesion, and a cork for terminating retraction to
maintain a priming complex for the next round of extension.
