FUR (Ferric uptake regulator) proteins are among the most important families of transcriptional regulators in prokaryotes, often behaving as global regulators. In the cyanobacterium Anabaena PCC 7120, FurB (Zur, Zinc uptake regulator) controls zinc and redox homeostasis through the repression of target genes in a zinc-dependent manner. In vitro, non-specific binding of FurB to DNA elicits protection against oxidative damage and avoids cleavage by deoxyribonuclease I. The present study provides, for the first time, evidence of the influence of redox environment in the interaction of FurB with regulatory zinc and its consequences in FurB–DNA-binding affinity. Calorimetry studies showed that, in addition to one structural Zn(II), FurB is able to bind two additional Zn(II) per monomer and demonstrated the implication of cysteine C93 in regulatory Zn(II) coordination. The interaction of FurB with the second regulatory zinc occurred only under reducing conditions. While non-specific FurB–DNA interaction is Zn(II)-independent, the optimal binding of FurB to target promoters required loading of two regulatory zinc ions. Those results combined with site-directed mutagenesis and gel-shift assays evidenced that the redox state of cysteine C93 conditions the binding of the second regulatory Zn(II) and, in turn, modulates the affinity for a specific DNA target. Furthermore, differential spectroscopy studies showed that cysteine C93 could also be involved in heme coordination by FurB, either as a direct ligand or being located near the binding site. The results indicate that besides controlling zinc homeostasis, FurB could work as a redox-sensing protein probably modifying its zinc and DNA-binding abilities depending upon environmental conditions.
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January 2018
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A 3D representation of the filamentous cyanobacteria Anabaena. In this issue, Sein-Echaluce et al. report on the molecular basis for the integration of environmental signals by FurB from Anabaena sp. PCC 7120; for details see pages 151–168.
Research Article|
January 05 2018
Molecular basis for the integration of environmental signals by FurB from Anabaena sp. PCC 7120
Violeta C. Sein-Echaluce;
Violeta C. Sein-Echaluce
1Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, 50009 Zaragoza, Spain
2Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Joint Unit IQFR-CSIC-BIFI, Universidad de Zaragoza, 50018 Zaragoza, Spain
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María Carmen Pallarés;
María Carmen Pallarés
3Laboratorio de Microscopías Avanzadas, Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain
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Anabel Lostao;
Anabel Lostao
3Laboratorio de Microscopías Avanzadas, Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain
4Fundación ARAID, 50018 Zaragoza, Spain
5Fundación INA, 50018 Zaragoza, Spain
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Inmaculada Yruela;
Inmaculada Yruela
6Estación Experimental de Aula Dei, Consejo Superior de Investigaciones Científicas (EEAD-CSIC), 50059 Zaragoza, Spain
7GBsC (BIFI, UNIZAR), Unidad Asociada al CSIC, Zaragoza, Spain
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Adrián Velázquez-Campoy;
Adrián Velázquez-Campoy
1Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, 50009 Zaragoza, Spain
2Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Joint Unit IQFR-CSIC-BIFI, Universidad de Zaragoza, 50018 Zaragoza, Spain
4Fundación ARAID, 50018 Zaragoza, Spain
7GBsC (BIFI, UNIZAR), Unidad Asociada al CSIC, Zaragoza, Spain
8Instituto de Investigación Sanitaria Aragón (IIS Aragon), 50009 Zaragoza, Spain
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M. Luisa Peleato;
M. Luisa Peleato
1Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, 50009 Zaragoza, Spain
2Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Joint Unit IQFR-CSIC-BIFI, Universidad de Zaragoza, 50018 Zaragoza, Spain
7GBsC (BIFI, UNIZAR), Unidad Asociada al CSIC, Zaragoza, Spain
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María F. Fillat
1Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, 50009 Zaragoza, Spain
2Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Joint Unit IQFR-CSIC-BIFI, Universidad de Zaragoza, 50018 Zaragoza, Spain
7GBsC (BIFI, UNIZAR), Unidad Asociada al CSIC, Zaragoza, Spain
Correspondence: María F. Fillat (fillat@unizar.es)
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Biochem J (2018) 475 (1): 151–168.
Article history
Received:
September 11 2017
Revision Received:
November 22 2017
Accepted:
December 04 2017
Accepted Manuscript online:
December 04 2017
Citation
Violeta C. Sein-Echaluce, María Carmen Pallarés, Anabel Lostao, Inmaculada Yruela, Adrián Velázquez-Campoy, M. Luisa Peleato, María F. Fillat; Molecular basis for the integration of environmental signals by FurB from Anabaena sp. PCC 7120. Biochem J 15 January 2018; 475 (1): 151–168. doi: https://doi.org/10.1042/BCJ20170692
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