2012-06-012024-05-15https://scholars.lib.ntu.edu.tw/handle/123456789/664537摘要：構成植物細胞壁之木質纖維素，主要由纖維素、半纖維素，以及木質素所組成。佔生物圈中有機碳源一半以上，為地球上產量最豐富的再生資源。半纖維素約佔木質纖維素組成之25-35%，為自然界中含量僅次纖維素的碳水化合物。半纖維素中的聚木糖主要由木糖聚合成主鏈，並包含多種不同糖類構成支鏈，故聚木糖需仰賴多種酵素共同作用。其中又以能分解β（1-4）木醣&#33527;鍵之聚木糖&#37238;最為重要，其能使大分子聚木糖水解成小分子的木寡醣、木二糖及木糖。因此，聚木糖&#37238;已廣泛應用於食品、飼料、造紙、生質酒精及農業廢棄物處理等用途。由於聚木糖&#37238;在工業使用時常在高溫環境下進行反應，因此，若能提高聚木糖&#37238;的活性與耐熱性，將可加速木質纖維素的水解及減少酵素使用量，對降低生產成本有極大的助益。本計畫擬針對一高活性的聚木糖&#37238;XynCDBFV及其與受質所形成的複合物進行晶體結構分析，以闡明其具有較高酵素活性與穩定性之原因。此外，並將依據理論設計法的原理，針對XynCDBFV的結構中，與受質結合及結構安定性有關的胺基酸殘基進行定點突變，期能更進一步提高其酵素活性與穩定性。<br> Abstract: Lignocellulose, which is composed mostly of cellulose, hemicellulose, and lignin, is the major components of plant cell wall materials and is one of the most abundant renewable resources on earth. Hemicellulose, constitutes about 25-35% of lignocellulose, is composed of xylan as a major component and is the second most abundant polysaccharide after cellulose. Xylan is a heteropolysaccharide that consists of a backbone of β-1,4-xylopyranosyl units and has substituent groups in its side chain. Therefore, complete hydrolysis of xylan requires the cooperation of a large number of xylanolytic enzymes. Of these xylanolytic enzymes, xylanase is of particular importance because it can depolymerize xylan by the random hydrolysis of β-1,4-xylosidic backbone linkages to produce xylooligosaccharides, xylobiose, and xylose. Thus xylanase has been used in a wide range of applications, such as food industry, animal feed, paper and pulp industry, and bioconversion of lignocellulosic material and agro-wastes to fermentative products. As many industrial hydrolysis processes are carried out at high temperature, increasing of xylanase activity and thermal stability would lead to better performance, i.e. decrease enzyme dosage, and thus decreased hydrolysis costs. In this study, three-dimensional structures of XynCDBFV, a xylanase showed high enzyme activity, will be studied by using X-ray crystallography. The site-directed mutation of the substrate binding site and structural-stability related amino acid residues of XynCDBFV will be constructed based on the principle of rational design. The hydrolytic activities and thermal stabilities of the mutant enzyme will be examined to evaluate its potential applications in industries.聚木糖&#37238X射線結晶分析法理論設計法定點突變xylanaseX-ray crystallographyrational designsite-directed mutation