Abstract
MmsR (33.3 kDa) is a putative LysR-type transcriptional activator of Pseudomonas denitrificans. With the help of 3-hydroxypropionic acid (3-HP), an important platform chemical, MmsR positively regulates the expression of mmsA, which encodes methylmalonylsemialdehyde dehydrogenase, the enzyme involved in valine degradation. In the present study, the cellular function of MmsR and its binding to the regulatory DNA sequence of mmsA expression were investigated both in vivo and in vitro. Transcription of the mmsA was enhanced >140-fold in the presence of 3-HP. In the MmsR-responsive promoter region, two operators showing dyad symmetry, designated O1 and O2 and centered at the -79 and -28 positions, respectively, were present upstream of the mmsA transcription start site. An electrophoretic mobility shift assay indicated that MmsR binds to both operator sites for transcription activation, probably in cooperative manner. When either O1 or O2 or both regions were mutated, the inducibility by the MmsR-3-HP complex was significantly reduced or completely removed, indicating that both sites are required for transcription activation. A 3-HP sensor was developed by connecting the activation of MmsR to a green fluorescent readout. A more than 50-fold induction by 25 mM 3-HP was observed.