Catalytically Promiscuous PLP-Dependent Aminotransferases Are Biocatalysts for C-C Bond Formation

Access to noncanonical amino acids is increasingly important in natural products synthesis and drug discovery. Enzymatic synthesis has emerged as an efficient strategy for simplifying approaches toward these molecules. Pyridoxal-5'-phosphate (PLP)-dependent enzymes have been extensively studied for the biocatalytic functionalization of α-amino acids. However, the high substrate specificity of these enzymes has limited the substrate scope of PLP-mediated biocatalysis. Efforts to identify generalist catalysts may be enabled by catalytic promiscuity, a property well-known in the PLP-dependent enzyme family. In pursuit of PLP-catalyzed C-C bond formation, we leverage a cofactor-centric approach with PLP-dependent enzymes not previously known to mediate C-C bond formation to access key nucleophilic intermediates. In this work, we show that aminotransferases Aro8 and TyrB can mediate C-C bond formation, the first such activity reported for aminotransferases. Further, this non-native function can be improved by the addition of a sacrificial ketoacid. Interestingly, Aro8 and TyrB exhibit distinct conformational dynamics that impact the diastereoselectivity of the reaction. These results indicate that aminotransferases are an untapped resource for the discovery of new biocatalysts for C-C bond formation and demonstrate the value of cofactor-guided reaction discovery.