Conformational stability of esterase enzymes from different sources.

In the last years we have performed a series of studies to characterize the conformational stability of three esterases from thermophilic and mesophilic sources: Aes esterase from Escherichia coli, EST2 from Alicyclobacillus acidocaldarius and AFEST from Archeoglobus fulgidus. These three esterases belong to the Hormone-sensitive lipase group of the superfamily of carboxylester hydrolases. The conformational stability of the three enzymes against temperature, urea and GuHCl has been determined by means of circular dichroism, fluorescence and differential scanning calorimetry measurements. Analysis of experimental data coupled with available structural information allowed us to suggest that the optimization of charge-charge interactions on the protein surface could one of the mechanisms to increase the thermal stability for the three esterases. This idea has been tested in the case of EST2, which shows a fully reversible thermal unfolding, by producing and studying variant forms of wild type enzyme in which a charged residue has been mutated. In the present article the obtained results are critically recollected in order to provide a clear and unified scenario.