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Abstract:
One hurdle to understanding how molecular machines function and evolve is our inability to see their structures in situ. Here we describe a minicell system that enables in situ cryogenic electron microscopy imaging and single particle analysis to probe the mechanisms and evolution of an iconic molecular machine, the bacterial flagellar motor, which spins a helical propeller for bacterial propulsion. Innovations in sample preparation and imaging enabled resolutions sufficient to build an in situ molecular model of the C. jejuni flagellar motor. Our results provide unprecedented insights into the in situ context of flagellar motors, highlight origins of recruited components involved in the unusually high torque of the C. jejuni motor, identify previously unknown components, and reveal corresponding modifications of core components. We also visualise structures involved in torque generation and secretion previously recalcitrant to structure determination. This technique will be of broad applicability to other large membrane-residing protein complexes. Note that this manuscript has a sibling manuscript titled “Evolution of a large periplasmic disk in Campylobacterota flagella facilitated efficient motility alongside autoagglutination” that dissects the function of the large disk described in this manuscript.Competing Interest StatementThe authors have declared no competing interest.
