Part:BBa_K1465302

Isobutanol pathway

Usage and Biology

Isobutanol is an important substance for industry. No known organism can produce isobutanol or other branched-chain alcohols. Atsumi et al. presented a metabolic pathway to produce isobutanol in Escherichia coli. The pathway is shown in Figure 1.

Figure 1: Schematic illustration of the isobutanol pathway

The shown pathway starts with pyruvate and results in isobutanol. We also start with pyruvate which is generated from 3-phosphogylcerate in the glycolysis of the cell.
The steps in the conversion of pyruvate to 2-ketoisovalerate can be executed by proteins existing in E. coli (IlvIH, IlvC and IlvD). Since E. coli also has an alcohol dehydrogenase (AdhE), the only required protein for the isobutanol production is a ketoisovalerate decarboxylase. This protein (KivD) can be received from Lactococcus lactis. The pathway shown in Figure 1 is already an improvement of the described way. The native protein IlvIH is replaced by the AlsS from Bacillus subtilis to increase the isobutanol production. (Atsumi et al.)
As we want to integrate this pathway in E.coli we used and improved existing BioBricks from the iGEM team NCTU Formosa 2011/2012. We used gene coding sequences of four out of five required proteins for the isobutanol production.
These genes are

• alsS (BBa_K539627)
• ilvC (BBa_K539621)
• ilvD (BBa_K539626)
• kivD (BBa_K539742)

The coding sequence of the gene of Adh (alcohol dehydrogenase), the fifth required protein, was not available as a BioBrick but because of E.coli's own AdhE the pathway works (Atsumi et al., 2008).