Photoinduced Electron Transfer in a Radical SAM Enzyme Generates an S-Adenosylmethionine Derived Methyl Radical.
J Am Chem Soc
; 141(40): 16117-16124, 2019 10 09.
Article
en En
| MEDLINE
| ID: mdl-31509404
ABSTRACT
Radical SAM (RS) enzymes use S-adenosyl-l-methionine (SAM) and a [4Fe-4S] cluster to initiate a broad spectrum of radical transformations throughout all kingdoms of life. We report here that low-temperature photoinduced electron transfer from the [4Fe-4S]1+ cluster to bound SAM in the active site of the hydrogenase maturase RS enzyme, HydG, results in specific homolytic cleavage of the S-CH3 bond of SAM, rather than the S-C5' bond as in the enzyme-catalyzed (thermal) HydG reaction. This result is in stark contrast to a recent report in which photoinduced ET in the RS enzyme pyruvate formate-lyase activating enzyme cleaved the S-C5' bond to generate a 5'-deoxyadenosyl radical, and provides the first direct evidence for homolytic S-CH3 bond cleavage in a RS enzyme. Photoinduced ET in HydG generates a trapped â¢CH3 radical, as well as a small population of an organometallic species with an Fe-CH3 bond, denoted ΩM. The â¢CH3 radical is surprisingly found to exhibit rotational diffusion in the HydG active site at temperatures as low as 40 K, and is rapidly quenched whereas 5'-dAdo⢠is stable indefinitely at 77 K, â¢CH3 quenches with a half-time of â¼2 min at this temperature. The rapid quenching and rotational/translational freedom of â¢CH3 shows that enzymes would be unable to harness this radical as a regio- and stereospecific H atom abstractor during catalysis, in contrast to the exquisite control achieved with the enzymatically generated 5'-dAdoâ¢.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
S-Adenosilmetionina
/
Hidrolasas
/
Proteínas Hierro-Azufre
/
Metano
Idioma:
En
Revista:
J Am Chem Soc
Año:
2019
Tipo del documento:
Article
País de afiliación:
Estados Unidos