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The tortoise beats the hare again

Grasping substrate tenaciously more important than speed in crystalline cellulose degradation

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Graduate School of Agricultural and Life Sciences / Faculty of Agriculture
2014/03/20

Cellulose is one of the main components of the plant cell wall and the most abundant biopolymer on Earth. However, the conversion of cellulose to other useful compounds such as alcohols and carbonates is difficult because of its high crystallinity and resistance to degradation. In nature, filamentous fungi (mushrooms and molds) produce a kind of cellulase, an enzyme possessing a unique tunnel-like structure and that can degrade crystalline cellulose, enabling the fungi to utilize cellulose as a source of energy. Understanding the process by which they do so may open the way to more efficient use of cellulose.

© Masahiro Samejima and Kiyohiko Igarashi.
(Top) The values of tenacity (processivity) and speed (velocity of reaction) of single molecules of long-tunneled ascomycete (mold) cellulase (TrCel7A) and short-tunneled basidiomycete (mushroom) cellulase (PcCel7C and PcCel7D) on a crystalline cellulose surface were compared. (Bottom) Biochemical comparison showed that the enzyme which has higher processivity is more effective at degrading crystalline cellulose.

In the present research, the research group of Professor Masahiro Samejima, Associate Professor Kiyohiko Igarashi, and graduate student Akihiko Nakamura at the University of Tokyo, Graduate School of Agricultural and Life Sciences Department of Biomaterial Sciences, and researchers from Kanazawa University observed the movements of three kinds of cellulases from filamentous fungi on crystalline cellulose by high-speed atomic force microscopy and compared their kinetic parameters. As a result, just as in ‘The Hare and the Tortoise’ from Aesop’s Fables, it was revealed that tenacity was more important than speed when degrading crystalline cellulose. In other words, the tenacity (processivity: the number of reactions per reaction initiation) is more important than the speed (velocity) of hydrolytic reaction of single molecules degrading crystalline cellulose. It is thought that this is because of the limited number of points on the crystalline cellulose surface at which cellulase can initiate reactions.

This result will be helpful when designing enzymes for more effective use of cellulose biomass resources.

Paper

Akihiko Nakamura, Hiroki Watanabe, Takuya Ishida, Takayuki Uchihashi, Masahisa Wada, Toshio Ando, Kiyohiko Igarashi and Masahiro Samejima,
“Trade-off between processivity and hydrolytic velocity of cellobiohydrolases at the surface of crystalline cellulose”,
The Journal of the American Chemical Society Online Edition: 2014/2/26, doi: 10.1021/ja4119994.
Article link

Links

Graduate School of Agricultural and Life Sciences

Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences

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