Characterisation and engineering of thermostable PLP-dependent alpha-oxoamine synthases (AOSs); versatile C-C bond...

The toolbox of C-C bond forming biocatalysts is forever expanding as demand increases for new and sustainable routes to organic molecules. One class of enzymes, the pyridoxal 5'-phosphate (PLP)-dependent α-oxoamine synthases (AOSs), have recently attracted attention as an alternative biocatalyst to the already industrially-useful aldolases and carboligases. The AOSs are able to catalyse the irreversible formation of versatile aminoketone building blocks from readily-available, renewable feedstocks such as amino acids and carboxylic acids. A wild type, heat-stable ThAOS has been successfully coupled with the Knorr-pyrrole reaction (KPR) in a chemoenzymatic cascade to form 24 unique pyrroles. The synthetic utility was further expanded by a rational engineering campaign targeting a V79 residue which structural studies revealed was close to the active site. The V79 variants were more stable and displayed a much broader substrate scope, enabling the production of over 80 aminoketone targets. These included products derived from unnatural acids and inexpensive acyl-thioesters. This chapter aims to encourage the reader to implement the C-C bond forming ThAOS biocatalysts in their strategies for organic synthesis.