7-Carboxy-7-deazaguanine synthase: A radical S-adenosyl-L-methionine enzyme with polar tendencies

Nathan A. Bruender, Tsehai A.J. Grell, Daniel P. Dowling, Reid M. McCarty, Catherine L. Drennan, Vahe Bandarian

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


Radical S-adenosyl-L-methionine (SAM) enzymes are widely distributed and catalyze diverse reactions. SAM binds to the unique iron atom of a site-differentiated [4Fe-4S] cluster and is reductively cleaved to generate a 5'-deoxyadenosyl radical, which initiates turnover. 7-Carboxy-7-deazaguanine (CDG) synthase (QueE) catalyzes a key step in the biosynthesis of 7-deazapurine containing natural products. 6-Carboxypterin (6-CP), an oxidized analogue of the natural substrate 6-carboxy-5,6,7,8-tetrahydropterin (CPH4), is shown to be an alternate substrate for CDG synthase. Under reducing conditions that would promote the reductive cleavage of SAM, 6-CP is turned over to 6-deoxyadenosylpterin (6-dAP), presumably by radical addition of the 5'-deoxyadenosine followed by oxidative decarboxylation to the product. By contrast, in the absence of the strong reductant, dithionite, the carboxylate of 6-CP is esterified to generate 6-carboxypterin-5'-deoxyadenosyl ester (6-CP-dAdo ester). Structural studies with 6-CP and SAM also reveal electron density consistent with the ester product being formed in crystallo. The differential reactivity of 6-CP under reducing and nonreducing conditions highlights the ability of radical SAM enzymes to carry out both polar and radical transformations in the same active site.

Original languageEnglish (US)
Pages (from-to)1912-1920
Number of pages9
JournalJournal of the American Chemical Society
Issue number5
StatePublished - Feb 8 2017

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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