Environmental factors modulating the stability and enzymatic activity of the Petrotoga mobilis Esterase (PmEst)

Enzymes isolated from thermophilic organisms found in oil reservoirs can find applications in many fields, including the oleochemical, pharmaceutical, bioenergy, and food/dairy industries. In this study, in silico identification and recombinant production of an esterase from the extremophile bacteria Petrotoga mobilis (designated PmEst) were performed. Then biochemical, bioinformatics and structural characterizations were undertaken using a combination of synchrotron radiation circular dichroism (SRCD) and fluorescence spectroscopies to correlate PmEst stability and hydrolytic activity on different substrates. The enzyme presented a high Michaelis-Menten constant (KM 0.16 mM) and optimum activity at ~55°C for p-nitrophenyl butyrate. The secondary structure of PmEst was preserved at acid pH, but not under alkaline conditions. PmEst was unfolded at high concentrations of urea or guanidine through apparently different mechanisms. The esterase activity of PmEst was preserved in the presence of ethanol or propanol and its melting temperature increased ~8°C in the presence of these organic solvents. PmEst is a mesophilic esterase with substrate preference towards short-to medium-length acyl chains. The SRCD data of PmEst is in agreement with the prediction of an α/β protein, which leads us to assume that it displays a typical fold of esterases from this family. The increased enzyme stability in organic solvents may enable novel applications for its use in synthetic biology. Taken together, our results demonstrate features of the PmEst enzyme that indicate it may be suitable for applications in industrial processes, particularly, when the use of polar organic solvents is required

Molecular basis for temperature sensing by an RNA thermometer

Regulatory RNA elements, like riboswitches, respond to intracellular signals by three-dimensional (3D) conformational changes. RNA thermometers employ a similar strategy to sense temperature changes in the cell and regulate the translational machinery. We present here the first 3D NMR structure of the functional domain of a highly conserved bacterial RNA thermometer containing the ribosome binding site that remains occluded at normal temperatures (30°C). We identified a region adjacent to the Shine–Dalgarno sequence that has a network of weak hydrogen bonds within the RNA helix. With the onset of heat shock at 42°C, destabilisation of the RNA structure initiates at this region and favours the release of the ribosome binding site and of the start codon. Deletion of a highly conserved G residue leads to the formation of a stable regular RNA helix that loses thermosensing ability. Our results indicate that RNA thermometers are able to sense temperature changes without the aid of accessory factors