Fine-tuning of a radical-based reaction by radical S-adenosyl-L-methionine tryptophan lyase

Science. 2016 Mar 18;351(6279):1320-3. doi: 10.1126/science.aad8995.


The radical S-adenosyl-L-methionine tryptophan lyase NosL converts L-tryptophan into 3-methylindolic acid, which is a precursor in the synthesis of the thiopeptide antibiotic nosiheptide. Using electron paramagnetic resonance spectroscopy and multiple L-tryptophan isotopologues, we trapped and characterized radical intermediates that indicate a carboxyl fragment migration mechanism for NosL. This is in contrast to a proposed fragmentation-recombination mechanism that implied Cα-Cβ bond cleavage of L-tryptophan. Although NosL resembles related tyrosine lyases, subtle substrate motions in its active site are responsible for a fine-tuned radical chemistry, which selects the Cα-C bond for disruption. This mechanism highlights evolutionary adaptation to structural constraints in proteins as a route to alternative enzyme function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon-Carbon Lyases / chemistry*
  • Catalytic Domain
  • Electron Spin Resonance Spectroscopy
  • Indoles / metabolism*
  • S-Adenosylmethionine / chemistry*
  • Streptomyces / enzymology*
  • Tryptophan / chemistry*
  • Tryptophanase / chemistry*


  • Indoles
  • S-Adenosylmethionine
  • Tryptophan
  • Carbon-Carbon Lyases
  • S-adenosyl-L-methionine tryptophan lyase, Streptomyces actuosus
  • Tryptophanase