Kinase-active Signaling Complexes of Bacterial Chemoreceptors Do Not Contain Proposed Receptor−Receptor Contacts Observed in Crystal Structures

摘要

The receptor dimers that mediate bacterial chemotaxis form high-order signaling complexes withnCheW and the kinase CheA. From the packing arrangement in two crystal structures of different receptorncytoplasmic fragments, two differentmodels have been proposed for receptor signaling arrays: the trimers-of-ndimers and hedgerow models. Here we identified an interdimer distance that differs substantially in the twonmodels, labeled the atoms defining this distance through isotopic enrichment, and measured it with 19nF-13nCnREDOR. This was done in two types of receptor samples: isolated bacterial membranes containingnoverexpressed, intact receptor and soluble receptor fragments reconstituted into kinase-active signalingncomplexes. In both cases, the distance found was not compatible with the receptor dimer-dimer contactsnobserved in the trimers-of-dimers or in the hedgerow models. Comparisons of simulated and observednREDOR dephasing were used to deduce a closest approach distance at this interface, which provides anconstraint for the possible arrangements of receptor assemblies.