There is a growing demand in the chemical and pharmaceutical industry to replace traditional chemical catalysis with environmentally benign approaches for the synthesis of high-value compounds. Enzyme-mediated transformations, i.e. using enzymes as catalysts, generally offer sustainability in combination with high selectivity and catalytic activity. However, most naturally occurring enzymes do not meet the requirements of large-scale industrial processes and/or do not catalyse new-to-nature reactions that are of relevance to the chemical and pharmaceutical industry with sufficient efficiency. As a consequence, the design of enzymes and protein therapeutics with tailored, new-to-nature properties is a long-standing goal in enzymology and cell biology. Nature generally uses 20 amino acids as building blocks for protein synthesis. However, this portfolio limits the options for engineering proteins with ‘un-natural’ activities. Recent developments in the expansion of the genetic code have the potential to revolutionise the design of novel enzymes; by reprogramming the genetic code, we could convey novel functionality into proteins and extend their properties. THIAZOLIUMenzyme aimed at incorporating thiazolium amino acids into the active site of promiscuous and highly evolvable de novo enzymes for orchestrating organocatalytic transformations of clinical and industrial interest. Such reactions, conventionally mediated by non-enzymatic, small molecule N-heterocyclic carbene (NHC) catalysts require high temperature and catalyst loading. It was envisioned that an engineered enzyme with the ability to catalyse such chemistry could overcome the drawbacks of these abiological catalysts, serving as a ‘greener’ biocatalytic alternative, and also perform the desired reactions in cells for medicinal purposes.
