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Synthesis of β‑Branched Tryptophan Analogues Using an Engineered Subunit of Tryptophan Synthase

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journal contribution
posted on 29.06.2016, 00:00 by Michael Herger, Paul van Roye, David K. Romney, Sabine Brinkmann-Chen, Andrew R. Buller, Frances H. Arnold
We report that l-threonine may substitute for l-serine in the β-substitution reaction of an engineered subunit of tryptophan synthase from Pyrococcus furiosus, yielding (2S,3S)-β-methyltryptophan (β-MeTrp) in a single step. The trace activity of the wild-type β-subunit on this substrate was enhanced more than 1000-fold by directed evolution. Structural and spectroscopic data indicate that this increase is correlated with stabilization of the electrophilic aminoacrylate intermediate. The engineered biocatalyst also reacts with a variety of indole analogues and thiophenol for diastereoselective C–C, C–N, and C–S bond-forming reactions. This new activity circumvents the 3-enzyme pathway that produces β-MeTrp in nature and offers a simple and expandable route to preparing derivatives of this valuable building block.