Purification and properties of an acetyl specific carboxylesterase from Nocardia mediterranei

Two Novel Acetylesterases from Pantoea dispersa: Recombinant Expression, Purification, and Characterization

Two novel acetylesterases from Pantoea dispersa, with low amino acid sequence identity between them, were expressed in Escherichia coli with a carboxyl-His₆ tail given by the expression plasmid, purified, and characterized. The purified proteins, named Est-1 and Est-2, had a molecular mass of 33 kDa and 37 kDa, respectively. Both proteins presented a modeled structure of homodimers with monomers presenting the α/β-hydrolase fold, with the catalytic triad Ser-Asp-His present in the active site. The K_M for p-nitrophenyl acetate and V_max values found for Est-1 were of 1.4 ± 0.2 mM and 8.66 ± 0.59 μmol/min and for Est-2 were of 0.36 ± 0.077 mM and 6.13 ± 0.56 μmol/min, respectively. Both enzymes presented an optimum pH of 7.0. The optimum temperature for Est-1 was 40 °C and for Est-2 was 50 °C. The temperatures in which the enzymes Est-1 and Est-2 lost half of their activity (T₅₀) were 44.1 and 58.9 °C, respectively. SDS, EDTA, and PMSF significantly inhibited the enzymes. The two purified enzymes also presented activity against triacetin and were able to deacetylate the carbohydrates pectin and xylan, with higher activity against pectin. Thus, they could be considered as carbohydrate esterases.

Rifamycins: strain improvement program

Rifamycins are primarily produced by Gram-positive bacterium Amycolatopsis mediterranei, which belongs to the order Actinomycetales. These antibiotics, apart from their application against pathogens of tuberculosis and leprosy, have also been found to be effective against several other pathogens including Mycobacterium avium and Pneumococcus. Because of the importance of rifamycin, the producer strain A. mediterranei has been genetically manipulated since 1957 in order to develop a strain that can either produce larger amounts of rifamycin or derivatives of rifamycin. In this article, the importance of the producer strain, traditional methods (mutations and recombination) of strain improvement, their limitations, and the development of a cloning vector and transformation methods that have made recombinant DNA techniques accessible for genetic manipulations of A mediterranei are discussed.