Directed evolution of enzymatic silicon-carbon bond cleavage in siloxanes

• Published in: Science (American Association for the Advancement of Science) Vol. 383; no. 6681; pp. 438 - 443
• Main Authors: Sarai, Nicholas S., Fulton, Tyler J., O’Meara, Ryen L., Johnston, Kadina E., Brinkmann-Chen, Sabine, Maar, Ryan R., Tecklenburg, Ron E., Roberts, John M., Reddel, Jordan C. T., Katsoulis, Dimitris E., Arnold, Frances H.
• Format: Journal Article
• Language: English
• Published: WASHINGTON Amer Assoc Advancement Science 26.01.2024; The American Association for the Advancement of Science
• Subjects: Bioaccumulation; Carbon; Cleavage; Consumer products; Cytochrome P450; Cytochromes P450; Directed evolution; Evolution; Hydroxylation; Multidisciplinary Sciences; Organosilicon compounds; Oxidation; Science & Technology; Science & Technology - Other Topics; Silicon; Siloxanes; OCTAMETHYLCYCLOTETRASILOXANE; CYTOCHROME-P450; METABOLITES; KINETICS; VOLATILE METHYL SILOXANES
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.adi5554

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 P450 BM3 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. Methylsiloxanes are organosilicon compounds produced by humans for use in a wide range of consumer products. Because they are not naturally found in nature, they are not readily degraded by organisms and some also have the potential to bioaccumulate. Sarai et al . identified a cytochrome P450 enzyme that can perform a hydroxylation on the methyl groups of linear methylsiloxanes. They then expanded this activity using directed evolution, creating variants that were more efficient and also functioned on cyclic methylsiloxanes. Mechanistic experiments suggested that a second oxidation and an enzyme-facilitated rearrangement can lead to cleavage of the carbon–silicon bond and release of formaldehyde. —Michael A. Funk An engineered enzyme catalyzes two sequential methyl group oxidations that lead to carbon–silicon bond cleavage in siloxanes.