A dual role of the transcriptional regulator TstR provides insights into cyanide detoxification in L actobacillus brevis

• Published in: Molecular microbiology 2014-05, Vol.92 (4), p.853-871
• Main Authors: Pagliai, Fernando A., Murdoch, Caitlin C., Brown, Sara M., Gonzalez, Claudio F., Lorca, Graciela L.
• Format: Article
• Language: English
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.12598

In this study we uncover two genes in L actobacillus brevis   ATCC 367, tstT and tstR , encoding for a rhodanese and a transcriptional regulator involved in cyanide detoxification. TstT ( LVIS _0852) belongs to a new class of thiosulphate:cyanide sulphurtransferases. We found that TstR ( LVIS _0853) modulates both the expression and the activity of the downstream‐encoded tstT . The TstR binding site was identified at −1 to +33, from tstR transcriptional start site. EMSA revealed that sulphite, a product of the reaction catalysed by TstT , improved the interaction between TstR : P tstR , while F e( III ) disrupted this interaction. Site‐directed mutagenesis in TstR identified M 64 as a key residue in sulphite recognition, while residues H 136‐ H 139‐ C 167‐ M 171 formed a pocket for ferric iron co‐ordination. In addition to its role as a transcriptional repressor, TstR is also involved in regulating the thiosulphate:cyanide sulphurtransferase activity of TstT . A threefold increase in TstT activity was observed in the presence of TstR , which was enhanced by the addition of F e( III ). Overexpression of the tstRT operon was found to increase the cyanide tolerance of L . brevis and E scherichia coli . The protein–protein interaction between TstR and TstT described herein represents a novel mechanism for regulation of enzymatic activity by a transcriptional regulator.