In-cell structural dissection of the type IVa pilus machine by cryo-electron tomography

Cryo-electron tomography (cryoET) enables cells to be imaged in 3-dimensions in an essentially
native state to macromolecular resolutions. It has allowed us to visualize the structures of
complex molecular machines in their native cellular context. In many cases, such machines
cannot be purified intact for in vitro studies. In other cases, the function of a machine is lost
outside the cell, so that the mechanism can be understood only by observation in situ. When
many copies of a machine are imaged, subtomogram averaging can be used to enhance signal
over noise and create even higher resolution images. Through comparing the results obtained
from the same machine possessing different component mutants or in different functional states,
structural component maps can be unravelled and activity proposed to provide mechanistic
insights. In this presentation, I will use the bacterial type IVa pilus machine as an example to
demonstrate how such cryoET analysis has helped us understand the mechanism of this dynamic
molecular grappling hook for bacterial cell motility.

References:
1. Yi-Wei Chang, Lee A Rettberg, Anke Treuner-Lange, Janet Iwasa, Lotte Søgaard-
Andersen, Grant J Jensen. ‘Architecture of the type IVa pilus machine.’ Science 351:
aad2001 (2016)
2. Anke Treuner-Lange, Yi-Wei Chang, Timo Glatter, Marco Herfurth, Steffi Lindow,
Georges Chreifi, Grant J Jensen, Lotte Søgaard-Andersen. ‘PilY1 and minor pilins form a
complex priming the type IVa pilus in Myxococcus xanthus’ Nature Communications 11:
5054 (2020)