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The effectors and sensory sites of formaldehyde-responsive regulator FrmR and metal-sensing variant.

Osman, Deenah and Piergentili, Cecilia and Chen, Junjun and Sayer, Lucy and Usón, Isabel and Huggins, Thomas and Robinson, Nigel and Pohl, Ehmke (2016) 'The effectors and sensory sites of formaldehyde-responsive regulator FrmR and metal-sensing variant.', Journal of biological chemistry., 291 (37). pp. 19502-19516.


The DUF156 family of DNA-binding, transcriptional-regulators include metal-sensors which respond to cobalt and/or nickel (RcnR, InrS) or copper (CsoR), plus CstR which responds to persulfide, and formaldehyde-responsive FrmR. Unexpectedly, the allosteric mechanism of FrmR from Salmonella enterica serovar Typhimurium is triggered by metals in vitro and variant FrmRE64H gains responsiveness to Zn(II) and cobalt in vivo. Here we establish that the allosteric mechanism of FrmR is triggered directly by formaldehyde in vitro. Sensitivity to formaldehyde requires a cysteine (Cys35 in FrmR) conserved in all DUF156 proteins. A crystal structure of metal- and formaldehyde-sensing FrmRE64H reveals that an FrmR-specific amino-terminal Pro2 is proximal to Cys35 and these residues form the deduced formaldehyde-sensing site. Evidence is presented which implies that residues spatially close to the conserved cysteine tune the sensitivities of DUF156 proteins above or below critical thresholds for different effectors, generating the semblance of specificity within cells. Relative to FrmR, RcnR is less responsive to formaldehyde in vitro and RcnR does not sense formaldehyde in vivo, but reciprocal mutations FrmRP2S and RcnRS2P respectively impair or enhance formaldehyde-reactivity in vitro. Formaldehyde-detoxification by FrmA requires S-(hydroxymethyl)glutathione, yet glutathione inhibits formaldehyde detection by FrmR in vivo and in vitro. Quantifying the number of FrmR molecules per cell and modelling formaldehyde modification as a function of [formaldehyde], demonstrates that FrmR-reactivity is optimised such that FrmR is modified, and frmRA de-repressed, at lower [formaldehyde] than required to generate S-(hydroxymethyl)glutathione. Expression of FrmA is thereby coordinated with the accumulation of its substrate.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Publisher statement:This final published version is available under a Creative Commons CC-BY license.
Date accepted:29 July 2016
Date deposited:01 August 2016
Date of first online publication:29 July 2016
Date first made open access:No date available

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