ยท D.
Verger, R. Rose, E. Paci, G. Costakes, T. Daviter, S. Hultgren, H. Remaut, A.
Ashcroft, S. Radford, and G. Waksman.
Structural and functional insights into the adaptor subunit function of PapF in
pilus biogenesis
Structure.
In Press
(2008).
P pili
are important adhesive fibers involved in kidney infection by uropathogenic Escherichia coli. Pilus subunits are
characterized by a large groove resulting from the lack of a beta-strand.
Polymerization of pilus subunits occurs via the donor-strand exchange (DSE) mechanism initiated when the
N-terminus of an incoming subunit interacts with the P5 region/pocket of the
previously-assembled subunit groove. Here, we solve the structure of
the PapD:PapF complex in order to understand why PapF undergoes slow DSE. The
structure reveals that the PapF P5 pocket is partially obstructed. MD
simulations show this region of PapF is flexible compared with its equivalent
in PapH, a subunit that also has an obstructed P5 pocket and is unable to
undergo DSE. Using electrospray-ionization mass spectrometry, we show that
mutations in the P5 region result in increased DSE rates. Thus, partial
obstruction of the P5 pocket serves as a modulating mechanism of DSE.