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Sarai NS, Fulton TJ, O'Meara RL, Johnston KE, Brinkmann-Chen S, Maar RR, Tecklenburg RE, Roberts JM, Reddel JCT, Katsoulis DE, Arnold FH. Directed evolution of enzymatic silicon-carbon bond cleavage in siloxanes. Science 2024; 383:438-443. [PMID: 38271505 DOI: 10.1126/science.adi5554] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2023] [Accepted: 12/18/2023] [Indexed: 01/27/2024]
Abstract
Volatile methylsiloxanes (VMS) are man-made, nonbiodegradable chemicals produced at a megaton-per-year scale, which leads to concern over their potential for environmental persistence, long-range transport, and bioaccumulation. We used directed evolution to engineer a variant of bacterial cytochrome P450BM3 to break silicon-carbon bonds in linear and cyclic VMS. To accomplish silicon-carbon bond cleavage, the enzyme catalyzes two tandem oxidations of a siloxane methyl group, which is followed by putative [1,2]-Brook rearrangement and hydrolysis. Discovery of this so-called siloxane oxidase opens possibilities for the eventual biodegradation of VMS.
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Affiliation(s)
- Nicholas S Sarai
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Tyler J Fulton
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Ryen L O'Meara
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Kadina E Johnston
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Sabine Brinkmann-Chen
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | | | | | | | | | | | - Frances H Arnold
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
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Rücker C, Winkelmann M, Kümmerer K. Are Si-C bonds formed in the environment and/or in technical microbiological systems? ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:91492-91500. [PMID: 37486465 PMCID: PMC10439844 DOI: 10.1007/s11356-023-28528-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 06/27/2023] [Indexed: 07/25/2023]
Abstract
Organosiloxanes are industrially produced worldwide in millions of tons per annum and are widely used by industry, professionals, and consumers. Some of these compounds are PBT (persistent, biaccumulative and toxic) or vPvB (very persistent and very bioaccumulative). If organosiloxanes react at all in the environment, Si-O bonds are hydrolyzed or Si-C bonds are oxidatively cleaved, to result finally in silica and carbon dioxide. In strong contrast and very unexpectedly, recently formation of new Si-CH3 bonds from siloxanes and methane by the action of microorganisms under mild ambient conditions was proposed (in landfills or digesters) and even reported (in a biotrickling filter, 30 °C). This is very surprising in view of the harsh conditions required in industrial Si-CH3 synthesis. Here, we scrutinized the pertinent papers, with the result that evidence put forward for Si-C bond formation from siloxanes and methane in technical microbiological systems is invalid, suggesting such reactions will not occur in the environment where they are even less favored by conditions. The claim of such reactions followed from erroneous calculations and misinterpretation of experimental results. We propose an alternative explanation of the experimental observations, i.e., the putative observation of such reactions was presumably due to confusion of two compounds, hexamethyldisiloxane and dimethylsilanediol, that elute at similar retention times from standard GC columns.
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Affiliation(s)
- Christoph Rücker
- Institute for Sustainable Chemistry, Leuphana University Lüneburg, Universitätsallee 1, 21335, Lüneburg, Germany.
| | - Magnus Winkelmann
- Institute for Sustainable Chemistry, Leuphana University Lüneburg, Universitätsallee 1, 21335, Lüneburg, Germany
| | - Klaus Kümmerer
- Institute for Sustainable Chemistry, Leuphana University Lüneburg, Universitätsallee 1, 21335, Lüneburg, Germany
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