Paradigm Shift for Radical S-Adenosyl-l-methionine Reactions: The Organometallic Intermediate Ω Is Central to Catalysis.

Journal Article (Journal Article)

Radical S-adenosyl-l-methionine (SAM) enzymes comprise a vast superfamily catalyzing diverse reactions essential to all life through homolytic SAM cleavage to liberate the highly reactive 5'-deoxyadenosyl radical (5'-dAdo·). Our recent observation of a catalytically competent organometallic intermediate Ω that forms during reaction of the radical SAM (RS) enzyme pyruvate formate-lyase activating-enzyme (PFL-AE) was therefore quite surprising, and led to the question of its broad relevance in the superfamily. We now show that Ω in PFL-AE forms as an intermediate under a variety of mixing order conditions, suggesting it is central to catalysis in this enzyme. We further demonstrate that Ω forms in a suite of RS enzymes chosen to span the totality of superfamily reaction types, implicating Ω as essential in catalysis across the RS superfamily. Finally, EPR and electron nuclear double resonance spectroscopy establish that Ω involves an Fe-C5' bond between 5'-dAdo· and the [4Fe-4S] cluster. An analogous organometallic bond is found in the well-known adenosylcobalamin (coenzyme B12) cofactor used to initiate radical reactions via a 5'-dAdo· intermediate. Liberation of a reactive 5'-dAdo· intermediate via homolytic metal-carbon bond cleavage thus appears to be similar for Ω and coenzyme B12. However, coenzyme B12 is involved in enzymes catalyzing only a small number (∼12) of distinct reactions, whereas the RS superfamily has more than 100 000 distinct sequences and over 80 reaction types characterized to date. The appearance of Ω across the RS superfamily therefore dramatically enlarges the sphere of bio-organometallic chemistry in Nature.

Full Text

Duke Authors

Cited Authors

  • Byer, AS; Yang, H; McDaniel, EC; Kathiresan, V; Impano, S; Pagnier, A; Watts, H; Denler, C; Vagstad, AL; Piel, J; Duschene, KS; Shepard, EM; Shields, TP; Scott, LG; Lilla, EA; Yokoyama, K; Broderick, WE; Hoffman, BM; Broderick, JB

Published Date

  • July 18, 2018

Published In

Volume / Issue

  • 140 / 28

Start / End Page

  • 8634 - 8638

PubMed ID

  • 29954180

Pubmed Central ID

  • PMC6053644

Electronic International Standard Serial Number (EISSN)

  • 1520-5126

Digital Object Identifier (DOI)

  • 10.1021/jacs.8b04061


  • eng

Conference Location

  • United States