Fiber-enriched fuel

New discoveries by Weizmann Institute of Science scientists may pave the way for the production of biofuel on an industrial scale

Tree trimmings, discarded corncobs or even recycled paper can be an excellent source of carbon for renewable energy production. All that is required for this is to break down the hard cellulose (cellulose) in the plant cell walls into smaller, more soluble sugars - not an easy job at all. An important step towards its realization was made in a study by scientists from the Weizmann Institute of Science and the Ludwig Maximilian University in Munich that was published in the scientific journal Proceedings of the American Academy of Sciences (PNAS). The scientists revealed important structural features of the cellulosome, a large enzyme complex found in microorganisms in soil and water, which breaks down the cell wall of plants. The new discoveries may promote the development of artificial cellulose for the production of biofuel on an industrial scale.

The cellulosome was discovered in the early 80s of the last century by Prof. Ed Bayer from the Department of Biomolecular Sciences of the Weizmann Institute of Science and Prof. Raphael Lemmed from Tel Aviv University. Since then, many efforts have been devoted - including by Prof. Bayer himself - to the production of artificial cellulose "to order", adapted for use in industry.

In the new study, Prof. Bayer and Dr. Yoav Barak from the Department of Chemical Research Infrastructures teamed up with Prof. Don Lamb, Dr. Anders Barrett and Prof. Willa Hendrix from the Ludwig Maximilian University in Munich, in order to find out how different subunits of the cellulosome are arranged in space. In the past, scientists had difficulty obtaining this information because the structure of the cellulosome is dynamic: the subunits change their position relative to each other. The scientists were able to overcome this obstacle using an advanced technology called smFRET, in which fluorescent tags attached to individual molecules make it possible to measure the mobility of these molecules in time frames of less than a thousandth of a second. The scientists used cellulosome from the bacterium Clostridium thermocellum, which is capable of turning cellulose directly into ethanol.

The research revealed that protein complexes called cohesins, the main building blocks of the cellulosome that serve as attachment sites for the enzymes that make it up, are not arranged on a scaffold one after the other, but are constantly in motion. While the subunits of the cellulosome are held together by long, flexible "ropes" that vibrate and twist continuously, cohesins from two adjacent subunits react to each other and change position. Thus they "dance" around each other until they find the optimal position to place the decomposition enzymes. This structural flexibility allows the cellulosome to connect in the most efficient way to the much larger cellulose molecule, and to break it down. The results of the experiment were confirmed using a computer model that simulates, at the level of the single atom, the reactions between different molecules of cohesin.

These findings may help design artificial cellulose for future use in industry, which could break down agricultural waste, non-edible agricultural crops and other forms of plant biomass, including man-made products such as paper waste. All this in order to efficiently produce biofuel that can replace the depleting reserves of oil, coal and natural gas.