Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 55, Issue 14, Pages 9817-9825Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.0c08811
Keywords
quantum mechanics/molecular mechanics; fluoroacetate dehalogenase; polyfluorinated compounds; perfluorinated compounds; rate-determining step; C-F bond activation
Categories
Funding
- National Major Science and Technology Program for Water Pollution Control and Treatment [2017zx07202-002]
- National Natural Science Foundation of China [21507073, 22077029]
- Young Scholars Program of Shandong University [2018WLJH54]
- Huxiang High-level Talent Gathering Project of Hunan Province [2019RS1040]
- [Ts201712003]
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The study systematically investigated the catalytic mechanism of the FAcD enzyme towards its natural substrate fluoroacetate. It was found that nucleophilic attack is the rate-determining step in the enzymatic transformation. The research also showed the potential of FAcD for defluorination of difluoroacetate, providing insights for rational enzyme engineering strategies to degrade fluorochemicals for environmental sustainability.
Fluorochemicals are persistent, bioaccumulative, and toxic compounds that are widely tributed in the environment. Developing efficient biodegradation strategies to decompose the fluorochemicals via breaking the inert C-F bonds presents a holistic challenge. As a promising biodegradation enzyme candidate, fluoroacetate dehalogenase (FAcD) has been reported as the only non-metallic enzyme to catalyze the cleavage of the strong C-F bond. Here, we systematically investigated the catalytic actions of FAcD toward its natural substrate fluoroacetate using molecular dynamics simulations and quantum mechanism/molecular mechanism calculations. We propose that the enzymatic transformation involves four elementary steps, (I) C-F bond activation, (II) nucleophilic attack, (III) C-O bond cleavage, and (IV) proton transfer. Our results show that nucleophilic attack is the rate-determining step. However, for difluoroacetate and trifluoroacetate, C-F bond activation, instead of nucleophilic attack, becomes the rate-determining step. We show that FAcD, originally recognized as alpha-fluorocarboxylic acid degradation enzyme, can catalyze the defluorination of difluoroacetate to glyoxylate, which is captured by our high-resolution mass spectrometry experiments. In addition, we employed amino acid electrostatic analysis method to screen potential mutation hotspots for tuning FAcD's electrostatic environment to favor substrate conversion. The comprehensive understanding of catalytic mechanism will inform a rational enzyme engineering strategy to degrade fluorochemicals for benefits of environmental sustainability.
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