Sequential C-H Methylation Catalyzed by the B12 -Dependent SAM Enzyme TokK: Comprehensive Theoretical Study of Selectivities.
Chemistry
; 29(7): e202202995, 2023 Feb 01.
Article
em En
| MEDLINE
| ID: mdl-36321632
ABSTRACT
TokK is a B12 -dependent radical SAM enzyme involved in the biosynthesis of the ß-lactam antibiotic asparenomycinâ
A. It can catalyze three methylations on different sp3 -hybridized carbon positions to introduce an isopropyl side chain at the ß-lactam ring of pantetheinylated carbapenem. Herein, we report a quantum chemical study of the reaction mechanism of TokK. A stepwise ''push-pull'' radical relay mechanism is proposed for each methylation a 5'-deoxyadenosine radical first abstracts a hydrogen atom from the substrate in the active site, then methylcobalamin directionally donates a methyl group to the substrate. More importantly, calculations were able to uncover the origin of observed chemoselectivity and stereoselectivity for the first methylation and regioselectivity for the following two methylations. Further detailed distortion/interaction analysis can help to unravel the main factors controlling the selectivities. Our findings of sequential methylations by TokK could have profound implications for studying other B12 -dependent radical SAM enzymes.
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Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Beta-Lactamas
/
Metiltransferases
Idioma:
En
Revista:
Chemistry
Assunto da revista:
QUIMICA
Ano de publicação:
2023
Tipo de documento:
Article