Pyrethroid Carboxylesterase PytH from Sphingobium faniae JZ-2: Structure and Catalytic Mechanism.

Carboxylesterase PytH, isolated from the pyrethroid-degrading bacterium Sphingobium faniae JZ-2, could rapidly hydrolyze the ester bond of a wide range of pyrethroid pesticides, including permethrin, fenpropathrin, cypermethrin, fenvalerate, deltamethrin, cyhalothrin, and bifenthrin. To elucidate the catalytic mechanism of PytH, we report here the crystal structures of PytH with bifenthrin (BIF) and phenylmethylsulfonyl fluoride (PMSF) and two PytH mutants. Though PytH shares low sequence identity with reported α/β-hydrolase fold proteins, the typical triad catalytic center with Ser-His-Asp triad (Ser78, His230, and Asp202) is present and vital for the hydrolase activity. However, no contact was found between Ser78 and His230 in the structures we solved, which may be due to the fact that the PytH structures we determined are in their inactive or low-activity forms. The structure of PytH is composed of a core domain and a lid domain; some hydrophobic amino acid residues surrounding the substrate from both domains form a deeper and wider hydrophobic pocket than its homologous structures. This indicates that the larger hydrophobic pocket makes PytH fit for its larger substrate binding; both lid and core domains are involved in substrate binding, and the lid domain-induced core domain movement may make the active center correctly positioned with substrates. [ABSTRACT FROM AUTHOR]