2024-01-25 カリフォルニア工科大学(Caltech)
◆シロキサンは様々な製品に使用されており、その環境中での分解メカニズムについての研究が進行中です。新しい研究では、酵素がシロキサンのシリコン–カーボン結合を直接切断せず、代わりに酸化して結合をより容易に切断する仕組みが示されました。
＜関連情報＞
- https://www.caltech.edu/about/news/teaching-nature-to-break-man-made-chemical-bonds
- https://www.science.org/doi/10.1126/science.adi5554
シロキサンにおける酵素的ケイ素-炭素結合切断の指向的進化 Directed evolution of enzymatic silicon-carbon bond cleavage in siloxanes
NICHOLAS S. SARAI , TYLER J. FULTON , RYEN L. O’MEARA , KADINA E. JOHNSTON , […], AND FRANCES H. ARNOLD
Science Published:25 Jan 2024
DOI:https://doi.org/10.1126/science.adi5554
Editor’s summary
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
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.
