The Bacterial Flagellar Motor
The Bacterial Flagellar Motor: Co-operative switching, turnover, and mechano-chemistry in a biological macromolecular complex
The bacterial flagellar motor has long been a canonical macromolecular complex because of the relative ease with which its output, rotation of the extracellular parts of the flagellum, can be observed. The motor is built around a set of rings ~50 nm in diameter that spans the bacterial cell envelope, containing hundreds of protein molecules of several different types. Single motors can rotate at speeds in excess of 1000 revs per second, and can propel swimming bacteria at speeds on the order of 100 microns per second. Stochastic switching of single motors is modulated by a chemo-sensory system, allowing bacteria to navigate gradients of nutrients or other environmental factors. This talk will describe the application of a range of single-molecule methods that have been used to investigate how the flagellar motor works. In vivo imaging of GFP-labelled components of live, working motors has revealed that the motor is not a static structure, but that individual proteins are constantly replaced at rates on the order of 1 per minute. Localization at nanometre precision of labels attached to the motor, at sample rates up to 100 kHz, has also allowed observation of the mechanism of co-operative directional switching in the motor and of its mechanochemical cycle. New methods to introduce protein molecules labelled with small organic fluorophores into bacteria for fluorescence microscopy, and to template the assembly of the flagllar rotor with DNA nanostructures, will also be presented.