Background:The flagellar motor generates bidirectional rotation using the proteins FliG, FliM, and CheY and membrane-bound stator complexes. Results: The structures of portions of FliG and FliM in complex allow for insights into switching and structure. Conclusion: FliG MC and FliM M in a 1:1 complex may form the C-ring of the motor. Significance: Understanding motor structure is key to understanding its mechanism.

SummaryThe high-resolution structures of nearly all the proteins that comprise the bacterial flagellar motor switch complex have been solved; yet a clear picture of the switching mechanism has not emerged. Here we use NMR to characterize the interaction modes and solution properties of a number of these proteins, including several soluble fragments of the flagellar motor proteins FliM and FliG and the response-regulator CheY. We find that the switch signal, activated CheY, binds to a previously unidentified region of FliM, adjacent to the FliM-FliM interface. We also find that activated CheY and FliG bind with mutual exclusivity to this site on FliM, because their respective binding surfaces partially overlap. These data support a model of CheY-driven motor switching wherein the binding of activated CheY to FliM displaces the carboxy-terminal domain of FliG (FliG C ) from FliM, modulating the FliG C -MotA interaction, and causing the motor to switch rotational sense as required for chemotaxis.

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A high-resolution structure elucidates how water flows through aquaporin into and out of biological cells. [Also see Report by Kosinska Eriksson et al. ]

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measurements, stopped-flow fluorescence and ITC. We are using pyrene labeled DNA, IkBa, or NF-kb to study the fluorescence changes occurring during the enhanced dissociation process. Our results show that IkBa increases the dissociation rate of the DNA from the NF-kB complex in a concentration-dependent manner and with high efficiency. We also repeated the experiments using different DNA chains and different mutants of IkBa. We are also studying IkBb, which appears to stabilize the NF-kB/DNA interaction. Both IkBa and IkBb are able to form NF-kB/DNA/IkB ternary complexes. The rates of association and dissociation of DNA to form the ternary complexes was also measured and compared to interpret the kinetics of the enhanced dissociation process.

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