1] Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan [2] Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency, K's Gobancho 7, Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan [3].
1] Department of Physics, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan [2] Bio-AFM Frontier Research Center, College of Science and Engineering, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan [3].
Nat Commun. 2014 Jun 4;5:3975. doi: 10.1038/ncomms4975.
Processivity refers to the ability of synthesizing, modifying and degrading enzymes to catalyse multiple successive cycles of reaction with polymeric substrates without disengaging from the substrates. Since biomass polysaccharides, such as chitin and cellulose, often form recalcitrant crystalline regions, their degradation is highly dependent on the processivity of degrading enzymes. Here we employ high-speed atomic force microscopy to directly visualize the movement of two processive glycoside hydrolase family 18 chitinases (ChiA and ChiB) from the chitinolytic bacterium Serratia marcescens on crystalline β-chitin. The half-life of processive movement and the velocity of ChiA are larger than those of ChiB, suggesting that asymmetric subsite architecture determines both the direction and the magnitude of processive degradation of crystalline polysaccharides. The directions of processive movements of ChiA and ChiB are observed to be opposite. The molecular mechanism of the two-way traffic is discussed, including a comparison with the processive cellobiohydrolases of the cellulolytic system.
延伸性是指合成酶、修饰酶和降解酶在与聚合底物作用时，无需与底物脱离就能催化多个连续的反应循环的能力。由于生物质多糖，如几丁质和纤维素，通常形成难以降解的晶体区域，因此它们的降解高度依赖于降解酶的延伸性。在这里，我们使用高速原子力显微镜直接观察到来自糜腐质霉的两种延伸性糖苷水解酶家族 18 几丁质酶（ChiA 和 ChiB）在结晶β-几丁质上的运动。ChiA 延伸性运动的半衰期和速度大于 ChiB，这表明不对称亚基结构决定了结晶多糖的延伸性降解的方向和程度。观察到 ChiA 和 ChiB 的延伸性运动方向相反。讨论了双向运动的分子机制，包括与纤维素分解系统中的细胞二糖水解酶的比较。
