A Panel of TrpB Biocatalysts Derived from Tryptophan Synthase through the Transfer of Mutations that Mimic Allosteric Activation

• Published in: Angewandte Chemie International Edition 2016-09, Vol.55 (38), p.11577-11581
• Main Authors: Murciano-Calles, Javier, Romney, David K., Brinkmann-Chen, Sabine, Buller, Andrew R., Arnold, Frances H.
• Format: Article
• Language: English
• Subjects: Activation; Allosteric properties; Allosteric Regulation; allostery; Binding; Biocatalysis; Biocatalysts; Catalysts; Chemical synthesis; Displays; Engineering; Enzymes; Homology; Kinetics; Mimicry; Mutagenesis, Site-Directed; Mutation; Protein Binding; Protein Engineering; Protein Subunits - chemistry; Protein Subunits - genetics; Protein Subunits - metabolism; Pyrococcus furiosus - enzymology; Spectroscopic analysis; Substrates; Transformations; Tryptophan; Tryptophan synthase; Tryptophan Synthase - chemistry; Tryptophan Synthase - genetics; Tryptophan Synthase - metabolism
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201606242

Naturally occurring enzyme homologues often display highly divergent activity with non‐natural substrates. Exploiting this diversity with enzymes engineered for new or altered function, however, is laborious because the engineering must be replicated for each homologue. A small set of mutations of the tryptophan synthase β‐subunit (TrpB) from Pyrococcus furiosus, which mimics the activation afforded by binding of the α‐subunit, was demonstrated to have a similar activating effect in different TrpB homologues with as little as 57 % sequence identity. Kinetic and spectroscopic analyses indicate that the mutations function through the same mechanism: mimicry of α‐subunit binding. From these enzymes, we identified a new TrpB catalyst that displays a remarkably broad activity profile in the synthesis of 5‐substituted tryptophans. This demonstrates that allosteric activation can be recapitulated throughout a protein family to explore natural sequence diversity for desirable biocatalytic transformations. Better off alone: The tryptophan synthase enzyme complex is active toward a number of indole analogues. The β‐subunit (TrpB) performs the synthetically useful reaction but requires the α‐subunit to be fully active. Mutations from a re‐activated TrpB variant from Pyrococcus furiosus were transferred into homologous TrpB enzymes to generate a panel of stand‐alone TrpB catalysts, one of which is useful for making 5‐substituted tryptophans, an important biological motif.