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. Author manuscript; available in PMC: 2017 Sep 25.
Published in final edited form as: J Mol Biol. 2016 Mar 24;428(19):3776–3788. doi: 10.1016/j.jmb.2016.03.017

Fig. 7. Mechanistic summary of mutant receptor behaviors.

Fig. 7

The dynamic-bundle model of HAMP input-output signaling proposes a series of meta-stable conformational states, produced through opposing structural interactions of the HAMP and MH bundles, that range between kinase-off and kinase-on states. In the full-off state (OFF), HAMP is stably packed and the MH bundle is loosely packed. During sensory adaptation, the CheR methyltransferase acts on loosely packed modification sites of OFF-state receptors to shift their output toward the ON state. In the full-on state (ON), HAMP is loosely packed and the MH bundle is stably packed. The CheB enzyme acts on stably packed modification sites of ON-state receptors to shift their output toward the OFF state. MH bundles with intermediate stabilities along the OFF-ON conformational landscape are not substrates for either adaptation enzyme. Structural alterations in the TM2-control cable that destabilize the HAMP OFF and/or ON state can trap the receptor within this intermediate regime, preventing modification by one or both sensory adaptation enzymes.