Structural features of sensory two component systems: a synthetic biology perspective.

All living organisms include a set of signaling devices that confer the ability to dynamically perceive and adapt to the fluctuating environment. Two-component systems are part of this sensory machinery that regulates the execution of different genetic and/or biochemical programs in response to specific physical or chemical signals. In the last two decades, there has been tremendous progress in our molecular understanding on how signals are detected, the allosteric mechanisms that control intramolecular information transmission and the specificity determinants that guarantee correct wiring. All this information is starting to be exploited in the development of new synthetic networks. Connecting multiple molecular players, analogous to programming lines of code, can provide the resources to build new sophisticated biocomputing systems. The Synthetic Biology field is starting to revolutionize several scientific fields, such as biomedicine and agriculture, propelling the development of new solutions. Expanding the spectrum of available nanodevices in the toolbox is key to unleash its full potential. This review aims to discuss, from a structural perspective, how to take advantage of the vast array of sensor and effector protein modules involved in two-component systems for the construction of new synthetic circuits.

An allosteric switch ensures efficient unidirectional information transmission by the histidine kinase DesK from Bacillus subtilis.

Phosphorylation carries chemical information in biological systems. In two-component systems (TCSs), the sensor histidine kinase and the response regulator are connected through phosphoryl transfer reactions that may be uni- or bidirectional. Directionality enables the construction of complex regulatory networks that optimize signal propagation and ensure the forward flow of information. We combined x-ray crystallography, hybrid quantum mechanics/molecular mechanics (QM/MM) simulations, and systems-integrative kinetic modeling approaches to study phosphoryl flow through the Bacillus subtilis thermosensing TCS DesK-DesR. The allosteric regulation of the histidine kinase DesK was critical to avoid back transfer of phosphoryl groups and futile phosphorylation-dephosphorylation cycles by isolating phosphatase, autokinase, and phosphotransferase activities. Interactions between the kinase's ATP-binding domain and the regulator's receiver domain placed the regulator in two distinct positions in the phosphotransferase and phosphatase complexes, thereby determining whether a key glutamine residue in DesK was properly situated to assist in the dephosphorylation reaction. Moreover, an energetically unfavorable phosphotransferase conformation when DesK was not phosphorylated minimized reverse phosphoryl transfer. DesR dimerization and a dissociative phosphoryl transfer reaction also enforced the direction of phosphoryl flow. Shorter or longer distances between the phosphoryl acceptor and donor residues shifted the phosphoryl transfer equilibrium by modulating the stabilizing effect of the Mg2+ cofactor. These mechanisms control the directionality of signal transmission and show how structure-encoded allostery stores and transmits information in signaling systems.

Chemosensitizer effect of cisplatin-treated bladder cancer cells by phenazine-5,10-dioxides.

We determined the chemosensitizer effect of phenazine dioxide derivatives to cisplatin and the possible mechanism of action on bladder cancer cells. Anti-proliferative activity of nine phenazine dioxide derivatives in presence or absence of cisplatin was evaluated in two bladder tumor human cells T24 and 253 J and one non tumor cell line V79-4. The sensitizer effect of the combined treatment was determined by chromosomal aberrations and micronucleus test. A possible mechanism of action of the sensitizer compounds as HDACi was also investigated.The phenazine dioxide 2c combined with cisplatin induced a cell cycle arrest on bladder cancer cells and resensitize the invasive and cisplatin resistant 253 J cell line. The HDAC inhibitory activity appears as one of the mechanism of action of the compound. The low toxicity levels against normal cells point out the phenazine dioxide derivative 2c as a very good scaffold for further design of HDACi sensitizer agents.

Allosteric activation of bacterial response regulators: the role of the cognate histidine kinase beyond phosphorylation.

UNLABELLED: Response regulators are proteins that undergo transient phosphorylation, connecting specific signals to adaptive responses. Remarkably, the molecular mechanism of response regulator activation remains elusive, largely because of the scarcity of structural data on multidomain response regulators and histidine kinase/response regulator complexes. We now address this question by using a combination of crystallographic data and functional analyses in vitro and in vivo, studying DesR and its cognate sensor kinase DesK, a two-component system that controls membrane fluidity in Bacillus subtilis. We establish that phosphorylation of the receiver domain of DesR is allosterically coupled to two distinct exposed surfaces of the protein, controlling noncanonical dimerization/tetramerization, cooperative activation, and DesK binding. One of these surfaces is critical for both homodimerization- and kinase-triggered allosteric activations. Moreover, DesK induces a phosphorylation-independent activation of DesR in vivo, uncovering a novel and stringent level of specificity among kinases and regulators. Our results support a model that helps to explain how response regulators restrict phosphorylation by small-molecule phosphoryl donors, as well as cross talk with noncognate sensors. IMPORTANCE: The ability to sense and respond to environmental variations is an essential property for cell survival. Two-component systems mediate key signaling pathways that allow bacteria to integrate extra- or intracellular signals. Here we focus on the DesK/DesR system, which acts as a molecular thermometer in B. subtilis, regulating the cell membrane's fluidity. Using a combination of complementary approaches, including determination of the crystal structures of active and inactive forms of the response regulator DesR, we unveil novel molecular mechanisms of DesR's activation switch. In particular, we show that the association of the cognate histidine kinase DesK triggers DesR activation beyond the transfer of the phosphoryl group. On the basis of sequence and structural analyses of other two-component systems, this activation mechanism appears to be used in a wide range of sensory systems, contributing a further level of specificity control among different signaling pathways.

Structural modifications on the phenazine N,N'-dioxide-scaffold looking for new selective hypoxic cytotoxins.

We have identified phenazine 5,10-dioxides as prodrugs for antitumour therapy that undergo hypoxic-selective bioreduction to form cytotoxic species. Here, we investigated some structural modifications in order to find new selective hypoxic cytotoxins and to establish the structural requirements for adequate activity. Three different chemical-series were prepared and the clonogenic survival of V79 cells on aerobic and anaerobic conditions was determined. Electrochemical- and DNA-interaction studies were done for the most relevant derivatives. The new fluoro-derivative 7-fluoro-2-aminophenazine 5,10-dioxide displayed selective toxicity towards hypoxic V79 cells having adequate hypoxic cytotoxicity ratio (HCR=6.8) and being the most potent hypoxic cytotoxins (P=2.5 µM) described for this family of bioreductive agents. The reduction potential of the N-oxide moiety in this new fluoro-derivative was in the range for adequate bioreduction property. According to the fluorescence studies, the DNA-interaction mechanism was especially operative in the phenazine drugs more than in the corresponding prodrugs, phenazine dioxides.