TY - JOUR

T1 - Optimization of a heterologous mevalonate pathway through the use of variant HMG-CoA reductases

AU - Ma, Suzanne M

AU - Garcia, David E

AU - Redding-Johanson, Alyssa M

AU - Friedland, Gregory D

AU - Chan, Rossana

AU - Batth, Tanveer S

AU - Haliburton, John R

AU - Chivian, Dylan

AU - Keasling, Jay D

AU - Petzold, Christopher J

AU - Lee, Taek Soon

AU - Chhabra, Swapnil R

N1 - Copyright © 2011 Elsevier Inc. All rights reserved.

PY - 2011/9

Y1 - 2011/9

N2 - Expression of foreign pathways often results in suboptimal performance due to unintended factors such as introduction of toxic metabolites, cofactor imbalances or poor expression of pathway components. In this study we report a 120% improvement in the production of the isoprenoid-derived sesquiterpene, amorphadiene, produced by an engineered strain of Escherichia coli developed to express the native seven-gene mevalonate pathway from Saccharomyces cerevisiae (Martin et al. 2003). This substantial improvement was made by varying only a single component of the pathway (HMG-CoA reductase) and subsequent host optimization to improve cofactor availability. We characterized and tested five variant HMG-CoA reductases obtained from publicly available genome databases with differing kinetic properties and cofactor requirements. The results of our in vitro and in vivo analyses of these enzymes implicate substrate inhibition of mevalonate kinase as an important factor in optimization of the engineered mevalonate pathway. Consequently, the NADH-dependent HMG-CoA reductase from Delftia acidovorans, which appeared to have the optimal kinetic parameters to balance HMG-CoA levels below the cellular toxicity threshold of E. coli and those of mevalonate below inhibitory concentrations for mevalonate kinase, was identified as the best producer for amorphadiene (54% improvement over the native pathway enzyme, resulting in 2.5mM or 520 mg/L of amorphadiene after 48 h). We further enhanced performance of the strain bearing the D. acidovorans HMG-CoA reductase by increasing the intracellular levels of its preferred cofactor (NADH) using a NAD(+)-dependent formate dehydrogenase from Candida boidinii, along with formate supplementation. This resulted in an overall improvement of the system by 120% resulting in 3.5mM or 700 mg/L amorphadiene after 48 h of fermentation. This comprehensive study incorporated analysis of several key parameters for metabolic design such as in vitro and in vivo kinetic performance of variant enzymes, intracellular levels of protein expression, in-pathway substrate inhibition and cofactor management to enable the observed improvements. These metrics may be applied to a broad range of heterologous pathways for improving the production of biologically derived compounds.

AB - Expression of foreign pathways often results in suboptimal performance due to unintended factors such as introduction of toxic metabolites, cofactor imbalances or poor expression of pathway components. In this study we report a 120% improvement in the production of the isoprenoid-derived sesquiterpene, amorphadiene, produced by an engineered strain of Escherichia coli developed to express the native seven-gene mevalonate pathway from Saccharomyces cerevisiae (Martin et al. 2003). This substantial improvement was made by varying only a single component of the pathway (HMG-CoA reductase) and subsequent host optimization to improve cofactor availability. We characterized and tested five variant HMG-CoA reductases obtained from publicly available genome databases with differing kinetic properties and cofactor requirements. The results of our in vitro and in vivo analyses of these enzymes implicate substrate inhibition of mevalonate kinase as an important factor in optimization of the engineered mevalonate pathway. Consequently, the NADH-dependent HMG-CoA reductase from Delftia acidovorans, which appeared to have the optimal kinetic parameters to balance HMG-CoA levels below the cellular toxicity threshold of E. coli and those of mevalonate below inhibitory concentrations for mevalonate kinase, was identified as the best producer for amorphadiene (54% improvement over the native pathway enzyme, resulting in 2.5mM or 520 mg/L of amorphadiene after 48 h). We further enhanced performance of the strain bearing the D. acidovorans HMG-CoA reductase by increasing the intracellular levels of its preferred cofactor (NADH) using a NAD(+)-dependent formate dehydrogenase from Candida boidinii, along with formate supplementation. This resulted in an overall improvement of the system by 120% resulting in 3.5mM or 700 mg/L amorphadiene after 48 h of fermentation. This comprehensive study incorporated analysis of several key parameters for metabolic design such as in vitro and in vivo kinetic performance of variant enzymes, intracellular levels of protein expression, in-pathway substrate inhibition and cofactor management to enable the observed improvements. These metrics may be applied to a broad range of heterologous pathways for improving the production of biologically derived compounds.

KW - Bacterial Proteins/biosynthesis

KW - Candida/enzymology

KW - Delftia acidovorans/enzymology

KW - Escherichia coli/genetics

KW - Formate Dehydrogenases/biosynthesis

KW - Formates/metabolism

KW - Fungal Proteins/biosynthesis

KW - Hydroxymethylglutaryl-CoA Reductases, NAD-Dependent/biosynthesis

KW - Mevalonic Acid/metabolism

KW - Organisms, Genetically Modified/genetics

KW - Phosphotransferases (Alcohol Group Acceptor)/biosynthesis

KW - Sesquiterpenes/metabolism

U2 - 10.1016/j.ymben.2011.07.001

DO - 10.1016/j.ymben.2011.07.001

M3 - Journal article

C2 - 21810477

VL - 13

SP - 588

EP - 597

JO - Metabolic Engineering

JF - Metabolic Engineering

SN - 1096-7176

IS - 5

ER -