Limits...
Redox proteins of hydroxylating bacterial dioxygenases establish a regulatory cascade that prevents gratuitous induction of tetralin biodegradation genes.

Ledesma-García L, Sánchez-Azqueta A, Medina M, Reyes-Ramírez F, Santero E - Sci Rep (2016)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

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.

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.

No MeSH data available.


Related in: MedlinePlus

Model for the regulation of thn genes in response (a) to tetralin and (b) to non-metabolizable substrates.Blockage of electron transfer is represented by dotted crosses. The sizes of the circles indicate the relative abundance of that form of the protein according to the substrates supplied.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4814904&req=5

f7: Model for the regulation of thn genes in response (a) to tetralin and (b) to non-metabolizable substrates.Blockage of electron transfer is represented by dotted crosses. The sizes of the circles indicate the relative abundance of that form of the protein according to the substrates supplied.

Mentions: The in vivo model for thn gene regulation presented in Fig. 7 proposes that ThnA3 reports to the regulatory ThnR-ThnY system whether a potential inducer molecule is also a good substrate of the catabolic pathway, based in a redox sensory mechanism10. In recent years, much progress has been made in understanding how Fe-S clusters regulatory proteins reprogram the expression of genes in response to environmental stimuli. A challenging question is to relate both the in vitro reactions of Fe-S clusters with its physiological relevance24. Our model is quite unique, since ThnA3 is the only ferredoxin that takes part in oxidative hydroxylation of aromatic compounds known to be involved in regulation of gene expression. Therefore, it is a crucial question to elucidate the mechanism by which ThnA3 exerts its function.


Redox proteins of hydroxylating bacterial dioxygenases establish a regulatory cascade that prevents gratuitous induction of tetralin biodegradation genes.

Ledesma-García L, Sánchez-Azqueta A, Medina M, Reyes-Ramírez F, Santero E - Sci Rep (2016)

Model for the regulation of thn genes in response (a) to tetralin and (b) to non-metabolizable substrates.Blockage of electron transfer is represented by dotted crosses. The sizes of the circles indicate the relative abundance of that form of the protein according to the substrates supplied.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814904&req=5

f7: Model for the regulation of thn genes in response (a) to tetralin and (b) to non-metabolizable substrates.Blockage of electron transfer is represented by dotted crosses. The sizes of the circles indicate the relative abundance of that form of the protein according to the substrates supplied.
Mentions: The in vivo model for thn gene regulation presented in Fig. 7 proposes that ThnA3 reports to the regulatory ThnR-ThnY system whether a potential inducer molecule is also a good substrate of the catabolic pathway, based in a redox sensory mechanism10. In recent years, much progress has been made in understanding how Fe-S clusters regulatory proteins reprogram the expression of genes in response to environmental stimuli. A challenging question is to relate both the in vitro reactions of Fe-S clusters with its physiological relevance24. Our model is quite unique, since ThnA3 is the only ferredoxin that takes part in oxidative hydroxylation of aromatic compounds known to be involved in regulation of gene expression. Therefore, it is a crucial question to elucidate the mechanism by which ThnA3 exerts its function.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

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.

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.

No MeSH data available.


Related in: MedlinePlus