P450-catalyzed asymmetric cyclopropanation of electron-deficient olefins under aerobic conditions

A variant of P450 from Bacillus megaterium five mutations away from wild type is a highly active catalyst for cyclopropanation of a variety of acrylamide and acrylate olefins with ethyl diazoacetate (EDA). The very high rate of reaction enabled by histidine ligation allowed the reaction to be conducted under aerobic conditions. The promiscuity of this catalyst for a variety of substrates containing amides has enabled synthesis of a small library of precursors to levomilnacipran derivatives

Improved selectivity of an engineered multi-product terpene synthase

Mutation of the sesquiterpene synthase Cop2 was conducted with a high-throughput screen for the cyclization activity using a non-natural substrate. A mutant of Cop2 was identified that contained three amino acid substitutions. This mutant, 17H2, converted the natural substrate FPP into germacrene D-4-ol with 77% selectivity. This selectivity is in contrast to that of the parent enzyme in which germacrene D-4-ol is produced as 29% and α-cadinol is produced as 46% of the product mixture. The mutations were shown to each contribute to this selectivity, and a homology model suggested that the mutations lie near to the active site though would be unlikely to be targeted for mutation by rational methods. Kinetic comparisons show that 17H2 maintains a k_(cat)/K_M of 0.62 mM^(−1) s^(−1), which is nearly identical to that of the parent Cop2, which had a k_(cat)/K_M of 0.58 mM^(−1) s^(−1)

High-Throughput Screening for Terpene-Synthase-Cyclization Activity and Directed Evolution of a Terpene Synthase

The development of high-throughput assays can be extremely challenging, yet is essential for many applications in drug discovery and enzyme engineering

Engineering and In Vivo Applications of Riboswitches.

Riboswitches are common gene regulatory units mostly found in bacteria that are capable of altering gene expression in response to a small molecule. These structured RNA elements consist of two modular subunits: an aptamer domain that binds with high specificity and affinity to a target ligand and an expression platform that transduces ligand binding to a gene expression output. Significant progress has been made in engineering novel aptamer domains for new small molecule inducers of gene expression. Modified expression platforms have also been optimized to function when fused with both natural and synthetic aptamer domains. As this field expands, the use of these privileged scaffolds has permitted the development of tools such as RNA-based fluorescent biosensors. In this review, we summarize the methods that have been developed to engineer new riboswitches and highlight applications of natural and synthetic riboswitches in enzyme and strain engineering, in controlling gene expression and cellular physiology, and in real-time imaging of cellular metabolites and signals