| 摘要: | 全球石油的產量正逐年下降，可以利用植物細胞壁的木質纖維素生產的乙醇作為替代石油的新型燃料，以植物生產的乙醇具有可再生以及材料來源廣泛等優勢。然而纖維素之間的交互作用導致纖維素不容易被降解，需要經過複雜的處理程序才能破壞這些交互作用，以舊有的方式生產乙醇會面臨耗時、成本過多等問題。部分厭氧型微生物的纖維水解酵素可以將纖維素分解成單醣，再透過發酵作用形成乙醇。
熱纖梭菌 (Clostridium thermocellum) 能夠形成纖維質體，透過纖維質體上不同的纖維水解酵素之間的協同作用來分解纖維素。醣?水解?家族9 (Glycoside Hydrolase Family 9, GH9) 是纖維質體上種類最多的纖維水解酵素，能夠辨識並水解β-1, 4 醣?鍵。GH9的催化殘基為Glutamate。CtCel9具有內切?和外切?兩種酵素活性，可以作用在纖維素的結晶區以及不定型區。CtCel9為多模塊結構，包含了訊號胜?、催化結構域、纖維素結合域家族3、第一型錨蛋白。我們利用X光繞射指出了CtCel9N和CtCel9R Catalytic domain及CBM3c的結構，解析度分別為1.59 ?、1.62?。Catalytic domain的結構為 (α/α)6 barrel、由數條Loops組成Active site；CBM3c的結構為β-sandwich摺疊。
我們提出了CtCel9N及CtCel9R的結構，並指出兩者結構之間的差異。透過解出CtCel9N和CtCel9R的結構更加了解纖維水解?和纖維素之間的相互作用，且能做為未來生物工程改良的一個參考。
Global petroleum production is declining year by year, prompting the search for alternative fuels to replace petroleum. Ethanol derived from lignocellulosic materials found in plant cell walls is a promising candidate. Plant-based ethanol offers the advantages of being renewable and derived from a wide range of sources. However, the complex structure of cellulose presents challenges in its degradation, requiring intricate processes to break down its interactions. Traditional methods of ethanol production face issues such as time consumption and excessive costs. Certain anaerobic microorganisms possess cellulase enzymes capable of breaking down cellulose into glucose, which can then be fermented into ethanol.
Among these microorganisms, Clostridium thermocellum forms a cellulosome that synergistically decomposes cellulose through the action of various cellulase enzymes. Within the cellulosome, Glycoside Hydrolase Family 9 (GH9) represents the most diverse cellulase, capable of recognizing and hydrolyzing β-1, 4 glycosidic bonds. The catalytic residue in GH9 is Glutamate.
CtCel9, found in C. thermocellum, exhibits both endoglucanase and exoglucanase activities, enabling it to act on both the crystalline and amorphous regions of cellulose. CtCel9 has a multi-module structure consisting of a signal peptide, catalytic domain, cellulose-binding module family 3, and type I dockerin. The X-ray diffraction analysis of CtCel9N and CtCel9R catalytic domains and CBM3c revealed their structures at resolutions of 1.59 ? and 1.62 ?, respectively. The catalytic domain adopts a (α/α)6 barrel structure with an active site comprised of several loops, while CBM3c exhibits a β-sandwich fold.
Through the determination of CtCel9N and CtCel9R structures, we gain insights into the interaction between cellulase and cellulose, serving as a foundation for future bioengineering advancements and improvements. |
