Modified Isobutanol Production in Yeast Boosts Yield

Scientists at the Massachusetts Institute of Technology (MIT) have increased the amount of isobutanol manufactured by yeast through restricting the entire production process within the cell organelles called mitochondria.

During fermentation, yeast cells can make small amount of isobutanol, an alcohol that contains more energy than ethanol and is more suitable as a transport biofuel. The natural production process for isobutanol in yeast consists of stages that are compartmentalized in the mitochondria and cytoplasm of the cell. A precursor called pyruvate, a product from sugar breakdown, is first transported from cytoplasm into mitochondria where it is converted into an intermediate. This intermediate is transported back to the cytoplasm where it is converted by a set of enzymes into isobutanol. Getting all the enzymes to function only in the cytoplasm is not an easy feat and isobutanol yield by this approach was shown to be very low.

When the MIT researchers took the opposite approach – moving the cytoplasmic phase into the mitochondria and confining the process within this organelle – isobutanol yield increased by 260%. The team accomplished this by engineering the enzymes such that they each had a protein tag that identified them as destined for mitochondria. According to the report published in Nature Biotechnology, the compartmentalization had likely enhanced the process through greater local enzyme concentrations, increased availability of intermediates and reduced losses of intermediates as they are transported out of mitochondria.