Transmembrane chemoreceptors are central components in the sensory system that
mediates bacterial chemotaxis. Like many transmembrane proteins, these receptors are fully
active only if inserted in a lipid bilayer. This requirement presents a challenge for in vitro
analysis by many biochemical and structural techniques. The challenge is met by Nanodiscs,
soluble, nanoscale (~10 nm diameter) particles of lipid bilayer surrounded by an annulus of
amphipathic protein into which transmembrane proteins can be incorporated. Using
Nanodiscs, we documented that chemoreceptor dimers bend at a specific locus along their
300 Å long axis, discovered that conformational differences between chemoreceptor
signalling states were differential propensities of receptor helices to become momentarily
unstructured, and determined that chemoreceptor signalling complexes activate and control
the chemotaxis histidine kinase by altering its catalytic rate constant.
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