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bioRxiv · 10.1101/2021.09.03.458835

Allosteric mechanism of signal transduction in the two-component system histidine kinase PhoQ

Mensa, B.·Polizzi, N. F.·Molnar, K. S.·Natale, A. M.·Lemmin, T.·DeGrado, W. F.
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Abstract

Transmembrane signaling proteins couple extracytosolic sensors to cytosolic effectors. Here, we examine how binding of Mg2+ to the sensor domain of an E. coli two component histidine kinase (HK), PhoQ, modulates its cytoplasmic kinase domain. We use cysteine-crosslinking and reporter-gene assays to simultaneously and independently probe the signaling state of PhoQs sensor and autokinase domains in a set of over 30 mutants. Strikingly, conservative single-site mutants distant from the sensor or catalytic site strongly influence PhoQs ligand-sensitivity as well as the magnitude and direction of the signal, endowing diverse signaling characteristics without need for epistasis. Data from 35 mutants are explained by a semi-empirical 3-domain model in which the sensor, intervening HAMP, and catalytic domains can adopt kinase-promoting or inhibiting conformations, that are in allosteric communication. The catalytic and sensor domains intrinsically favor a constitutively kinase-on conformation, while the HAMP favors the off state; when coupled, they create a bistable system responsive to physiological [Mg2+]. Mutants alter signaling by locally modulating these intrinsic equilibrium constants and couplings. Our model suggests signals transmit via interdomain allostery rather than propagation of a single concerted conformational change, explaining the diversity of signaling structural transitions observed in individual HK domains.

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Mensa, B., Polizzi, N. F., Molnar, K. S., Natale, A. M., Lemmin, T., DeGrado, W. F.. 2021-09-05. Allosteric mechanism of signal transduction in the two-component system histidine kinase PhoQ. https://doi.org/10.1101/2021.09.03.458835

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