Trade-off between Processivity and Hydrolytic Velocity of Cellobiohydrolases at the Surface of Crystalline Cellulose

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• 作者：Akihiko Nakamura ; Hiroki Watanabe ; Takuya Ishida ; Takayuki Uchihashi ; Masahisa Wada ; Toshio Ando ; Kiyohiko Igarashi ; Masahiro Samejima
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：March 26, 2014
• 年：2014
• 卷：136
• 期：12
• 页码：4584-4592
• 全文大小：615K
• 年卷期：v.136,no.12(March 26, 2014)
• ISSN：1520-5126

文摘

Analysis of heterogeneous catalysis at an interface is difficult because of the variety of reaction sites and the difficulty of observing the reaction. Enzymatic hydrolysis of cellulose by cellulases is a typical heterogeneous reaction at a solid/liquid interface, and a key parameter of such reactions on polymeric substrates is the processivity, i.e., the number of catalytic cycles that can occur without detachment of the enzyme from the substrate. In this study, we evaluated the reactions of three closely related glycoside hydrolase family 7 cellobiohydrolases from filamentous fungi at the molecular level by means of high-speed atomic force microscopy to investigate the structure鈥揻unction relationship of the cellobiohydrolases on crystalline cellulose. We found that high moving velocity of enzyme molecules on the surface is associated with a high dissociation rate constant from the substrate, which means weak interaction between enzyme and substrate. Moreover, higher values of processivity were associated with more loop regions covering the subsite cleft, which may imply higher binding affinity. Loop regions covering the subsites result in stronger interaction, which decreases the velocity but increases the processivity. These results indicate that there is a trade-off between processivity and hydrolytic velocity among processive cellulases.