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Engineered Biosynthesis of β-Alkyl Tryptophan Analogs
preprintsubmitted on 13.07.2018, 02:00 and posted on 13.07.2018, 14:09 by Christina E. Boville, Remkes A. Scheele, Philipp Koch, Sabine Brinkmann-Chen, Andrew R. Buller, Frances H. Arnold
Non-canonical amino acids (ncAAs) with dual stereocenters at the α and β positions are valuable precursors to natural products and therapeutics. Despite the potential applications of such bioactive β-branched ncAAs, their availability is limited due to the inefficiency of the multi-step methods used to prepare them. Here we report a stereoselective biocatalytic synthesis of β-branched tryptophan analogs using an engineered variant of Pyrococcus furiosus tryptophan synthase (PfTrpB), PfTrpB7E6. PfTrpB7E6 is the first biocatalyst to synthesize bulky β-branched tryptophan analogs in a single step, with demonstrated access to 27 ncAAs. The molecular basis for the efficient catalysis and broad substrate tolerance of PfTrpB7E6 was explored through X-ray crystallography and UV-visible light spectroscopy, which revealed that a combination of active-site and remote mutations increase the abundance and persistence of a key reactive intermediate. PfTrpB7E6 provides an operationally simple and environmentally benign platform for preparation of β-branched tryptophan building blocks.