Purification and characterization of an intracellular esterase from a marine Fusarium fungal species showing phthalate diesterase activity

• An intracellular phthalate esterase was isolated from marine fungus Fusarium sp. DMT-5-3 with dimethyl isophthalate as the inducing substrate.
• The enzyme was able to hydrolyze dimethyl isophthalate and dimethyl terephthalate, but not dimethyl phthalate and three isomers of monomethyl phthalate esters (MMPEs), showing a high substrate specificity.
• The findings suggest that there are distinct esterases involved in hydrolysis of two carboxylic ester bonds of dimethyl phthalate esters by Fusarium sp. DMT-5-3.

An intracellular esterase was isolated from a marine fungus Fusarium sp. DMT-5-3 with dimethyl isophthalate (DMI) as the inducing substrate. The purified esterase is a dimeric protein consisting of two identical subunits. The molecular mass of the enzyme is about 76 kDa. The optimal temperature and pH for the esterase activity was 50 °C and 8.0, respectively. The enzyme remained stable between pH 6.0–12.0 and under 40 °C. The esterase activity was particularly activated by Mg2+ and inhibited by Cr3+, Cu2+, Hg2+, Zn2+, Ni2+, Co2+, Cd2+, and Mn2+. Substrate specificity analysis showed that the enzyme was capable of hydrolyzing DMI and dimethyl terephthalate (DMT), but not dimethyl phthalate (DMP) and three isomers of monomethyl phthalate esters (MMPEs). Compared with previously reported DMT esterase isolated from tested fungus, this DMI esterase showed smaller molecular mass but broader substrate specificity. These results suggested that phthalate esterases produced by Fusarium sp. DMT-5-3 are highly substrate-specific and there are distinct esterases involved in hydrolysis of two carboxylic ester bonds of dimethyl phthalate esters (DMPEs).