Redox-sensitive DNA binding by homodimeric Methanosarcina acetivorans MsvR is modulated by cysteine residues

BMC Microbiology (Impact Factor: 2.73). 07/2013; 13(1):163. DOI: 10.1186/1471-2180-13-163
Source: PubMed


Methanoarchaea are among the strictest known anaerobes, yet they can survive exposure to oxygen. The mechanisms by which they sense and respond to oxidizing conditions are unknown. MsvR is a transcription regulatory protein unique to the methanoarchaea. Initially identified and characterized in the methanogen Methanothermobacter thermautotrophicus (Mth), MthMsvR displays differential DNA binding under either oxidizing or reducing conditions. Since MthMsvR regulates a potential oxidative stress operon in M. thermautotrophicus, it was hypothesized that the MsvR family of proteins were redox-sensitive transcription regulators.
An MsvR homologue from the methanogen Methanosarcina acetivorans, MaMsvR, was overexpressed and purified. The two MsvR proteins bound the same DNA sequence motif found upstream of all known MsvR encoding genes, but unlike MthMsvR, MaMsvR did not bind the promoters of select genes involved in the oxidative stress response. Unlike MthMsvR that bound DNA under both non-reducing and reducing conditions, MaMsvR bound DNA only under reducing conditions. MaMsvR appeared as a dimer in gel filtration chromatography analysis and site-directed mutagenesis suggested that conserved cysteine residues within the V4R domain were involved in conformational rearrangements that impact DNA binding.
Results presented herein suggest that homodimeric MaMsvR acts as a transcriptional repressor by binding Ma PmsvR under non-reducing conditions. Changing redox conditions promote conformational changes that abrogate binding to Ma PmsvR which likely leads to de-repression.

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Available from: Daniel Lessner, Mar 17, 2014
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    • "One final set of strongly supported interactions include the repression of certain proteins involved in oxidative stress. As Isom et al. point out [81], the MsvR regulator is homologous to a well characterized variant in Methanothermobacter thermautotrophicus and 43 genes in addition to the msvR gene in M. acetivorans contain the two binding sequences upstream of the TATA box. Their study shows support for a homodimer with cysteine residues which likely are oxidized in an oxygen rich environment, causing the dimer to be released from the binding site. "
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