The Elusive 5'-Deoxyadenosyl Radical: Captured and Characterized by Electron Paramagnetic Resonance and Electron Nuclear Double Resonance Spectroscopies.

Journal Article (Journal Article)

The 5'-deoxyadenosyl radical (5'-dAdo·) abstracts a substrate H atom as the first step in radical-based transformations catalyzed by adenosylcobalamin-dependent and radical S-adenosyl-l-methionine (RS) enzymes. Notwithstanding its central biological role, 5'-dAdo· has eluded characterization despite efforts spanning more than a half-century. Here, we report generation of 5'-dAdo· in a RS enzyme active site at 12 K using a novel approach involving cryogenic photoinduced electron transfer from the [4Fe-4S]+ cluster to the coordinated S-adenosylmethionine (SAM) to induce homolytic S-C5' bond cleavage. We unequivocally reveal the structure of this long-sought radical species through the use of electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopies with isotopic labeling, complemented by density-functional computations: a planar C5' (2pπ) radical (∼70% spin occupancy); the C5'(H)2 plane is rotated by ∼37° (experiment)/39° (DFT) relative to the C5'-C4'-(C4'-H) plane, placing a C5'-H antiperiplanar to the ribose-ring oxygen, which helps stabilize the radical against elimination of the 4'-H. The agreement between φ from experiment and in vacuo DFT indicates that the conformation is intrinsic to 5-dAdo· itself, and not determined by its environment.

Full Text

Duke Authors

Cited Authors

  • Yang, H; McDaniel, EC; Impano, S; Byer, AS; Jodts, RJ; Yokoyama, K; Broderick, WE; Broderick, JB; Hoffman, BM

Published Date

  • July 31, 2019

Published In

Volume / Issue

  • 141 / 30

Start / End Page

  • 12139 - 12146

PubMed ID

  • 31274303

Pubmed Central ID

  • 31274303

Electronic International Standard Serial Number (EISSN)

  • 1520-5126

Digital Object Identifier (DOI)

  • 10.1021/jacs.9b05926

Language

  • eng

Conference Location

  • United States