Paper Report for: Xu_2020_Appl.Environ.Microbiol__

Carboxylesterase PytH, isolated from a 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, here we report the crystal structures of PytH with bifenthrin (BIF) and phenylmethylsulfonyl fluoride (PMSF) and two PytH mutants. Though PytH shares low sequence identity with reported alpha/beta-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 substrates 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.IMPORTANCE Pyrethroid pesticides are widely applied in agriculture and household, however, extensive use of these pesticides also causes serious environmental and health problems. The hydrolysis of pyrethroids by carboxylesterases is the major pathway of microbial degradation of pyrethroids, but the structure of carboxylesterases and its catalytic mechanism are still unknown. Carboxylesterase PytH from Sphingobium faniae JZ-2 could effectively hydrolyze a wide range of pyrethroid pesticides. The crystal structures of PytH are solved in this study. It showed that it belongs to the alpha/beta-hydrolase fold proteins with typical catalytic Ser-His-Asp triad though PytH has a low sequence identity (about 20%) with them. The special large hydrophobic binding pocket endowed PytH binding bigger pyrethroids family substrates. Our structures shed light on the substrate selectivity and the future application of PytH and deeper the understanding of alpha/beta-hydrolase members.