TY - JOUR
T1 - Photoinduced Electron Transfer in a Radical SAM Enzyme Generates an S-Adenosylmethionine Derived Methyl Radical
AU - Yang, Hao
AU - Impano, Stella
AU - Shepard, Eric M.
AU - James, Christopher D.
AU - Broderick, William E.
AU - Broderick, Joan B.
AU - Hoffman, Brian M.
N1 - Funding Information:
EPR, ENDOR, and photolysis experiments were funded by the NIH (GM 111097 to BMH). All work related to the preparation of HydG was funded by the U.S. Department of Energy, Office of Basic Energy Sciences grant DE-SC0005404 (to JBB and EMS). The synthesis of labeled SAMs was supported by the NIH (GM 54608 and 131889 to JBB). The authors thank Ryan Swimley (MSU) for his assistance with the preparation of HydG.
Publisher Copyright:
Copyright © 2019 American Chemical Society.
PY - 2019/10/9
Y1 - 2019/10/9
N2 - 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 •CH3 radical, as well as a small population of an organometallic species with an Fe-CH3 bond, denoted ωM. The •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, •CH3 quenches with a half-time of ∼2 min at this temperature.
AB - 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 •CH3 radical, as well as a small population of an organometallic species with an Fe-CH3 bond, denoted ωM. The •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, •CH3 quenches with a half-time of ∼2 min at this temperature.
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U2 - 10.1021/jacs.9b08541
DO - 10.1021/jacs.9b08541
M3 - Article
C2 - 31509404
AN - SCOPUS:85073080651
SN - 0002-7863
VL - 141
SP - 16117
EP - 16124
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 40
ER -