title: Redox proteins of hydroxylating bacterial dioxygenases establish a regulatory cascade that prevents gratuitous induction of tetralin biodegradation genes.
abstract: Bacterial dioxygenase systems are multicomponent enzymes that catalyze the initial degradation of many environmentally hazardous compounds. In Sphingopyxis granuli strain TFA tetralin dioxygenase hydroxylates tetralin, an organic contaminant. It consists of a ferredoxin reductase (ThnA4), a ferredoxin (ThnA3) and a oxygenase (ThnA1/ThnA2), forming a NAD(P)H-ThnA4-ThnA3-ThnA1/ThnA2 electron transport chain. ThnA3 has also a regulatory function since it prevents expression of tetralin degradation genes (thn) in the presence of non-metabolizable substrates of the catabolic pathway. This role is of physiological relevance since avoids gratuitous and wasteful production of catabolic enzymes. Our hypothesis for thn regulation implies that ThnA3 exerts its action by diverting electrons towards the regulator ThnY, an iron-sulfur flavoprotein that together with the transcriptional activator ThnR is necessary for thn gene expression. Here we analyze electron transfer among ThnA4, ThnA3 and ThnY by using stopped-flow spectrophotometry and determination of midpoint reduction potentials. Our results indicate that when accumulated in its reduced form ThnA3 is able to fully reduce ThnY. In addition, we have reproduced in vitro the regulatory circuit in the proposed physiological direction, NAD(P)H-ThnA4-ThnA3-ThnY. ThnA3 represents an unprecedented way of communication between a catabolic pathway and its regulatory system to prevent gratuitous induction.
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Seville, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Ledesma-García
authors.affiliation: Departamento de Bioquímica y Biología Molecular y Celular, and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Universidad de Zaragoza, Zaragoza, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Sánchez-Azqueta
authors.affiliation: Departamento de Bioquímica y Biología Molecular y Celular, and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Universidad de Zaragoza, Zaragoza, Spain.
authors.forename: Milagros
authors.initials: M
authors.lastname: Medina
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Seville, Spain.
authors.forename: Francisca
authors.initials: F
authors.lastname: Reyes-Ramírez
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Seville, Spain.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Santero
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001673:Biodegradation, Environmental; D004579:Electron Transport; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics / Q000378:metabolism; D004785:Environmental Pollutants / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005287:Ferredoxin-NADP Reductase / Q000235:genetics* / Q000378:metabolism; D005288:Ferredoxins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D042301:Sphingomonadaceae / Q000235:genetics / Q000378:metabolism; D013764:Tetrahydronaphthalenes / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D045222:Electron Transport Chain Complex Proteins; D004785:Environmental Pollutants; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D011994:Recombinant Proteins; D013764:Tetrahydronaphthalenes; D015534:Trans-Activators; D010105:Oxygenases; D005287:Ferredoxin-NADP Reductase; C095210:tetralin