Envision a future where the fuel for your car is brewed much like your favorite beer. This vision edges closer to reality with the advent of biofuel production, where tiny yeast cells are at the forefront of turning renewable organic materials into energy. However, these microbrewers face a challenge: they are sensitive to the very products they help create. Compounds like isobutanol, though promising for their superior fuel qualities, disrupt the delicate balance within yeast cells, posing a significant hurdle to biofuel production.

Addressing this obstacle, an inventive approach has been discovered that equips yeast with a protective layer against the harsh effects of isobutanol. Borrowing from nature’s playbook, it’s been found that proteins from higher organisms, known as annexins, can be introduced into yeast to reinforce their cellular barriers. Acting like a suit of armor, these proteins stabilize the cells’ outer layer, safeguarding them from biofuel-induced damage and marking a potential revolution in how we harness sustainable energy. This breakthrough not only aims to enhance biofuel production efficiency but also marks a significant stride in our journey towards greener energy solutions.

At the University of Virginia, Professor Carl Creutz has spearheaded a significant innovation that stands to dramatically improve the efficiency of producing biofuels. Documented in Scientific Reports, his study demonstrates how incorporating metazoan annexins into yeast cells arms them against the toxic impacts of isobutanol. This solution tackles a key issue in biofuel production: the negative effects of biofuels on crucial microorganisms involved in the fermentation process.

Producing biofuel, an integral strategy for renewable energy, is challenged by the toxicity of substances like isobutanol to yeast, essential for fermentation. Professor Creutz details the strategy undertaken, stating, “Adding metazoan calcium-dependent proteins that bind to cell membranes, known as annexins, can lessen the harmful effects of isobutanol on Saccharomyces cerevisiae life and complex membrane functions.” The essence of Creutz’s research lies in the protective nature of annexins. These proteins defend yeast cell membranes against damage from isobutanol, thus boosting yeast survival and preserving critical functions for fermentation. “The annexin may act like a ‘molecular bandage,’ focusing precisely on the sites of membrane damage,” Creutz suggests, explaining how these proteins operate.

Figure: Using annexins to protect cell membranes from biofuel toxicity.
Part a. An annexin protein (depicted by the red coils) binds to calcium ions crossing the membrane through a defect caused by the hydrophobic biofuel. The annexin repairs the leak by restoring the normal structure of the membrane. 
Part b. Annexins are produced inside the yeast cells by expression of genes from multicellular animals or plants.  Enough annexins are produced to cover all sites of membrane damage. 
Part c.  Production of the annexin enhances the viability of yeast in the presence of 2% isobutanol.  Yeast growth is detected by measuring the turbidity (cloudiness) of the yeast culture with a spectrophotometer (in absorbance units – abbreviated as A600).  After 24 hours in the isobutanol no yeast cell growth is seen if no annexin is being produced “none”.  Significant yeast cell growth occurs if one of three human annexins are being produced (ANX1, ANX2, or ANX6) or a worm (nematode) annexin (NEX1).
Part d.  After 48 hours in the isobutanol only the ANX6 and NEX1 cultures are still viable, indicating a superior membrane repair capability of these annexins.

Exploring the methodologies employed, Creutz utilized a blend of genetic engineering and thorough testing to highlight the annexins’ protective effects. By expressing various human and C. elegans annexins in yeast cells, the study assessed their capability to counteract the toxic effects of isobutanol, showcasing their role in scenarios ranging from direct growth inhibition to aiding the yeast’s ability to remodel its membrane when adapting to different growth environments.

In tests where yeast cultures faced isobutanol levels that typically inhibit growth, those modified to express annexins showed remarkable resilience compared to unaltered controls. This durability stems from the annexins’ ability to “repair” sites of membrane damage, allowing the yeast to flourish even under the challenging conditions imposed by isobutanol.

Additionally, the shift of yeast cells from glucose to galactose—a vital change requiring membrane modification for galactose absorption—was greatly assisted by annexins in the presence of isobutanol. This not only signifies a protective role against toxicity but also suggests an improvement in the yeast’s adaptive capabilities, crucial for biofuel production efficiency.

Beyond biofuel production, the implications of this study are vast, indicating potential applications across biotechnological fields by offering a novel method for improving microbial resilience against hydrophobic compounds. This could influence the manufacturing of pharmaceuticals and other chemicals, showcasing the wide-ranging applicability of annexin technology.

As we strive for sustainable energy solutions, Professor Creutz’s contributions represent a substantial leap forward. By leveraging the protective power of annexins, this research not only overcomes a major biofuel production challenge but also forges new pathways for biotechnological innovation, heralding an era where sustainable energy solutions are both more efficient and environmentally friendly.


Carl E. Creutz, Expression of Metazoan Annexins in Yeast Provides Protection Against Deleterious Effects of the Biofuel Isobutanol, Scientific Reports, 2019. DOI: https://doi.org/10.1038/s41598-019-55169-9.


Prof. Dr. Carl E. Creutz

Prof. Dr. Carl E. Creutz. After receiving a B.S. in Physics at Stanford University (1969), a M.S. in Physics from the University of Wisconsin (1970), and a Ph.D. in Biophysics from Johns Hopkins University (1976), Dr. Creutz conducted basic research in molecular and cell biology at the NIH in Bethesda, MD, as a Staff Fellow (1976-1979) and Senior Staff Fellow (1980-1981). In 1981, he was recruited to the Department of Pharmacology at the University of Virginia as an Assistant Professor. In 1987, he was promoted to Associate Professor, and in 1994 to Full Professor.  In 2003, Dr. Creutz was elected as the Harrison Professor of Medical Teaching in Pharmacology, a position he holds concurrently with his position as Professor of Pharmacology.