1. Structural Biology and Molecular Biophysics
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Usher Proteins: Lifting the lid on pilus assembly

  1. Han Remaut  Is a corresponding author
  2. Nir Ben-Tal  Is a corresponding author
  1. VIB Structural Biology Research Center, Belgium
  2. Tel-Aviv University, Israel
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Cite this article as: eLife 2014;3:e04997 doi: 10.7554/eLife.04997
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Many bacteria are covered with long protein fibers called pili that contain hundreds of pilus subunits.

These pili are assembled at usher proteins (above) that are embedded in the cell walls of bacteria; chaperone proteins are also involved in the assembly process. The usher protein recruits chaperone-subunit complexes, catalyzes the polymerization of the subunits, and allows passage of the pili to the cell surface. The usher protein must be activated in order to act as a catalyst; activation involves moving a ‘plug’ (purple) that blocks the channel in the protein (left) through an angle of ∼150° to open the channel (right). The movement of the plug also orients the domains (NTD, CTD1 and CTD2) that recruit the chaperone-subunit complexes (not shown). These models are based on X-ray structures of the PapC usher protein (PDB:2vqi; Remaut et al., 2008) and the FimD usher protein bound to a chaperone-subunit complex (PDB:3rfz; Phan et al., 2011; Geibel et al., 2013). Farabella et al. explored the roles of the alpha-helix (yellow) and the beta-hairpin (blue/grey) in the activation process.

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