Metabolic transistor strategy for controlling electron transfer chain in Escherichia coli

Hui Wu1,3, Leepika Tuli1, George N. Bennett2, Ka-Yiu San1,2*

1Department of Bioengineering, Rice University, Houston, Texas

2Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas

3State Key Laboratory of Bioreactor Engineering, East China University of Science and

Technology, Shanghai 200237, China

*Corresponding author: Telephone: 713-348-5361; Fax: 713-348-5877; E-mail: ksan@rice.edu

A novel metabolic transistor was built to finely control a large metabolic flux by a small change in the level or availability of a key participant in the large flux. The fine-tuning of the key participant in the large flux can be accomplished by adding a competitive reaction of a precursor or an intermediate in the biosynthetic pathway of the key participant. For use of oxygen there is the electron transport chain (ETC), also called the electron transport system (ETS), in E. coli and many industrially important organisms. This ETC contains various cytochromes and electron carriers, such as quinones- ubiquinones. Our recent strategy, which can control the level of oxidation via the ETC, is through regulating the production of the quinone by competing for an intermediate within its biosynthetic pathway. One approach is using the lycopene synthesis pathway to drain the isopentenyl diphosphate (IPP) pool; Another strategy is fine-tuning the reaction catalyzed by the geranyl diphosphate:4-hydroxybenzoate geranyltransferase from Lithospermum erythrorhizon (lePGT-1) to drain both the isopentenyl diphosphate (IPP) and 4-hydroxybenzoic acid (4-HB) pools. The achievement of a theoretical yield on lactate production under aerobic conditions via this metabolic control strategy upon manipulation of quinone synthesis pathway in E. coli strain, thus provides an in vivo means to genetically control the activity of the electron transfer chain and manipulate the production of reduced products. The advantage of this metabolic control approach is that it uses very little cell energy,
protein quantity, and carbon flux to control the major metabolic flux of the cell and can be finely tuned for optimal or desired level performance, in the manner of a transistor where a small current change is used to control a big current flow.