Perfluoro alkyl substances (PFAS) have received substantial attention recently due to environmental and health concerns. These substances are pervasive in the environment and are not readily degraded under normal conditions. It had been observed recently that the Acidimicrobiaceae sp. A6 can degrade the perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). To understand the mechanisms of the biodefluorination we have modeled the structures of a highly similar protein of the A6 from Acidimicrobiaceae bacterium TMED77. We have constructed structural models of TMED77 and TMED77-like proteins and examined an electron transfer mechanism for the biodegradation of PFOA/PFOS by TMED77. In this study, we systematically analyze the binding affinity of different PFAS substrates in the active site using docking and molecular dynamics simulations. Quantum mechanical/molecular mechanical (QM/MM) free energy (potential of mean force) simulations along the reaction coordinate provided the atomic details of the TMED77 defluorination mechanism, revealing key residues responsible for the catalysis, and suggesting potential mutations to engineer enzymes targeting specific PFAS substrates. In addition to our computational modeling, we have cloned the TMED77 gene and expressed this protein in Escherichia coli. The characterization of protein product will involve evaluation of its enzymatic dehalogenation activity towards PFAS compounds via NMR studies and its comparison with other reductive dehalogenases found in the literature (such as PceA). These modeling and experimental studies will aid in the understanding of PFAS degradation mechanisms.

Mechanism of per- and polyfluoroalkyl substances defluorination by Acidimicrobiaceae bacterium TMED77

ACS Fall 2021

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