title: Forcing the issue: aromatic tuning facilitates stimulus-independent modulation of a two-component signaling circuit.
abstract: Two-component signaling circuits allow bacteria to detect and respond to external stimuli. Unfortunately, the input stimulus remains unidentified for the majority of these circuits. Therefore, development of a synthetic method for stimulus-independent modulation of these circuits is highly desirable because particular physiological or developmental processes could be controlled for biotechnological purposes without the need to identify the stimulus itself. Here, we demonstrate that aromatic tuning, i.e., repositioning the aromatic residues commonly found at the cytoplasmic end of the receptor (EnvZ) transmembrane domain, facilitates stimulus-independent modulation of signal output from the EnvZ/OmpR osmosensing circuit of Escherichia coli. We found that these osmosensing circuits retained the ability to respond appropriately to increased external osmolarity, suggesting that the tuned receptors were not locked in a single conformation. We also noted that circuits containing aromatically tuned variants became more sensitive to changes in the receptor concentration than their wild-type counterpart, suggesting a new way to study mechanisms underpinning receptor concentration-dependent robustness. We believe that aromatic tuning has several advantages compared to previous methods aimed at stimulus-independent modulation of receptors and that it will be generally applicable to a wide-range of two-component circuits.
authors.affiliation: †Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kogle Alle 6, DK-2970 Hørsholm, Denmark.
authors.forename: Morten H H
authors.initials: MH
authors.lastname: Nørholm
authors.affiliation: ‡Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 16C, SE-10691 Stockholm, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: von Heijne
authors.forename: Roger R
authors.initials: RR
authors.lastname: Draheim
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D015398:Signal Transduction / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D015534:Trans-Activators; C112177:osmolarity response regulator proteins; C057843:envZ protein, E coli
keywords: aromatic tuning; concentration-dependent robustness; stimulus-independent modulation; two-component circuit engineering