A structure-function study of ZraP and ZraS provides new insights into the two-component system Zra

International audienceZra belongs to the envelope stress response (ESR) two-component systems (TCS). It is atypical because of its third periplasmic repressor partner (ZraP), in addition to its histidine kinase sensor protein (ZraS) and its response regulator (ZraR) components. Furthermore, although it is activated by Zn2+, it is not involved in zinc homeostasis or protection against zinc toxicity. Here, we mainly focus on ZraS but also provide information on ZraP

GFP-Like Phototransformation Mechanisms in the Cytotoxic Fluorescent Protein KillerRed Unraveled by Structural and Spectroscopic Investigations

KillerRed (KR) is a red fluorescent protein recognized as an efficient genetically encoded photosensitizer. KR generates reactive oxygen species <i>via</i> a complex process of photoreactions, ending up in photobleaching, the mechanism of which remains obscure. In order to clarify these mechanisms, we focus on a single mutant V44A (A44-KR) exhibiting the solely green component of KR. We report on the laser-induced structural transformations of A44-KR at cryogenic temperature, which we have investigated by combining UV–vis fluorescence/absorption spectroscopy with X-ray crystallography. Like the well-known GFP, A44-KR possesses a mixture of protonated (A) absorbing at 397 and deprotonated (B) absorbing at 515 nm chromophores, which are stressed by intense prolonged violet and blue laser sources. Both illuminations directly drive the B-chromophores toward a bleached <i>trans</i> isomerized form. A-type chromophores are sensitive only to violet illumination and are phototransformed either into a deprotonated green fluorescent form by decarboxylation of E218 or into a bleached form with a disordered <i>p</i>-hydroxybenzylidene. <i>In crystallo</i> spectroscopy at cryo-temperature allowed the identification and dissection of an exhaustive scheme of intermediates and end-products resulting from the phototransformation of A44-KR. This constitutes a framework for understanding the photochemistry of the photosensitizer KillerRed

Binding of the 2F5 Monoclonal Antibody to Native and Fusion-Intermediate Forms of Human Immunodeficiency Virus Type 1 gp41: Implications for Fusion-Inducing Conformational Changes

We investigated how the broadly neutralizing monoclonal antibody 2F5 affects the human immunodeficiency virus type 1 envelope glycoprotein as it undergoes receptor-induced conformational changes and show that 2F5 binds both native and fusion-intermediate conformations, suggesting inhibition of a late step in virus entry. We also demonstrate conformational changes in the C heptad of gp41

Low-temperature switching by photoinduced protonation in photochromic fluorescent proteins

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The Two-Component System ZraPSR Is a Novel ESR that Contributes to Intrinsic Antibiotic Tolerance in Escherichia coli

International audienceDuring their lifecycle, bacteria are exposed to continuous changes in their environment, some of which are stressful and can be harmful. The cell envelope is the first line of defense against a hostile environment, but it is also the first target for damage. To deal with this problem, bacteria have evolved systems collectively called "envelope stress response," or ESR, dedicated to the detection and repair of damaged components. Here we decided to investigate whether the atypical two-component system ZraP-SR is a novel ESR. Based on the screening of more than 240 drugs using the Biolog technology, we show that the deletion of zraP or zraR confers increased susceptibility to five classes of antibiotics and to some environmental stress targeting the envelope. Using a microscopy approach, we also establish that ZraP and ZraR are required to maintain envelope integrity. So far, the ZraR regulator was only known to activate the transcription of zraP and zraSR. Using chromatin immunoprecipitation followed by sequencing and RT-qPCR, we have now identified 25 additional genes regulated by ZraR, the majority of which are involved in the response against stress. Taken together, our results demonstrate that ZraP-SR is a novel ESR

Structural Basis for Metal Sensing by CnrX

International audienceCnrX is the metal sensor and signal modulator of the three-protein transmembrane signal transduction complex CnrYXH of Cupriavidus metallidurans CH34 that is involved in the setup of cobalt and nickel resistance. We have determined the atomic structure of the soluble domain of CnrX in its Ni-bound, Co-bound, or Zn-bound form. Ni and Co ions elicit a biological response, while the Zn-bound form is inactive. The structures presented here reveal the topology of intraprotomer and interprotomer interactions and the ability of metal-binding sites to fine-tune the packing of CnrX dimer as a function of the bound metal. These data suggest an allosteric mechanism to explain how the complex is switched on and how the signal is modulated by Ni or Co binding. These results provide clues to propose a model for signal propagation through the membrane in the complex

Biophysical and physiological characterization of ZraP from Escherichia coli, the periplasmic accessory protein of the atypical ZraSR two-component system.

International audienceThe ZraSR system belongs to the family of TCSs (two-component signal transduction systems). In Escherichia coli, it was proposed to participate in zinc balance and to protect cytoplasmic zinc overload by sequestering this metal ion into the periplasm. This system controls the expression of the accessory protein ZraP that would be a periplasmic zinc scavenger. ZraPSR is functionally homologous with CpxPAR that integrates signals of envelope perturbation, including misfolded periplasmic proteins. The auxiliary periplasmic regulator CpxP inhibits the Cpx pathway by interacting with CpxA. Upon envelope stress sensing, the inhibitory function of CpxP is relieved, resulting in CpxR activation. Similarly to CpxPAR, ZraPSR probably plays a role in envelope stress response as a zinc-dependent chaperone activity was demonstrated for ZraP in Salmonella. We have purified ZraP from E. coli and shown that it is an octamer containing four interfacial metal-binding sites contributing to dimer stability. These sites are located close to the N-terminus, whereas the C-terminus is involved in polymerization of the protein to form a tetramer of dimers. In vitro, ZraP binds copper with a higher affinity than zinc and displays chaperone properties partially dependent on zinc binding. In vivo, zinc-bound ZraP is a repressor of the expression of the zraPSR operon. However, we have demonstrated that none of the Zra proteins are involved in zinc or copper resistance. We propose an integrated mechanism in which zinc is a marker of envelope stress perturbation and ZraPSR TCS is a sentinel sensing and responding to zinc entry into the periplasm