Published in the Proceedings of the National Academy of Sciences, the study explains how cellobiose, a byproduct of cellulose, impedes its own breakdown, complicating the biofuel production process. Biofuels are typically produced by converting starch or cellulose to glucose, which is then fermented into ethanol. Although corn is currently a major biofuel source due to its efficient conversion process, it raises issues such as competition with food supplies and significant greenhouse gas emissions.
"Cellulose from non-edible plant parts offers a sustainable alternative, yet the slow breakdown process remains a significant barrier," said Charles Anderson, professor of biology at Penn State. The complexity stems from cellulose's crystalline structure and the presence of other compounds like xylan and lignin in cell walls, which traditional techniques failed to adequately analyze.
To better understand these molecular hindrances, the team employed a novel imaging technique. They chemically tagged cellulase enzymes with fluorescent markers and monitored them using the SCATTIRSTORM microscope, a device developed by Penn State for this specific purpose. This allowed the researchers to observe the enzymes' interaction with cellulose at a molecular level, providing insights previously obscured by larger-scale observational methods.
The enzyme Cel7A, crucial in the breakdown process, encounters issues when cellobiose accumulates at the enzyme's exit point, effectively blocking subsequent cellulose processing. This discovery sheds light on why removing cellobiose is challenging and costly, influencing the overall efficiency of biofuel production.
"Our understanding of these molecular mechanisms opens avenues to optimize cellulase enzymes and potentially reduce the enzymatic cost in biofuel production, which is about 50 cents per gallon," Anderson explained. This could make biofuels derived from plant waste more economically viable compared to fossil fuels or corn-based ethanol.
The findings build on previous research identifying xylan and lignin as additional barriers to efficient cellulose degradation. By addressing these molecular obstacles, the researchers aim to enhance the feasibility of second-generation biofuels, contributing to a more sustainable energy future.
Research Report:Single-molecule tracking reveals dual front door/back door inhibition of Cel7A cellulase by its product cellobiose
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