Journal
MOLECULAR MICROBIOLOGY
Volume 100, Issue 1, Pages 156-172Publisher
WILEY
DOI: 10.1111/mmi.13308
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- National Institute of General Medical Sciences of the National Institutes of Health [RO1 GM029481, 2 R25 GM060507]
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The Escherichia coli aerotaxis receptor, Aer, monitors cellular oxygen and redox potential via FAD bound to a cytosolic PAS domain. Here, we show that Aer-PAS controls aerotaxis through direct, lateral interactions with a HAMP domain. This contrasts with most chemoreceptors where signals propagate along the protein backbone from an N-terminal sensor to HAMP. We mapped the interaction surfaces of the Aer PAS, HAMP and proximal signalling domains in the kinase-off state by probing the solvent accessibility of 129 cysteine substitutions. Inaccessible PAS-HAMP surfaces overlapped with a cluster of PAS kinase-on lesions and with cysteine substitutions that crosslinked the PAS -scaffold to the HAMP AS-2 helix. A refined Aer PAS-HAMP interaction model is presented. Compared to the kinase-off state, the kinase-on state increased the accessibility of HAMP residues (apparently relaxing PAS-HAMP interactions), but decreased the accessibility of proximal signalling domain residues. These data are consistent with an alternating static-dynamic model in which oxidized Aer-PAS interacts directly with HAMP AS-2, enforcing a static HAMP domain that in turn promotes a dynamic proximal signalling domain, resulting in a kinase-off output. When PAS-FAD is reduced, PAS interaction with HAMP is relaxed and a dynamic HAMP and static proximal signalling domain convey a kinase-on output.
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