Structure and Functions of Polysaccharide-degrading Enzyme with High Activity under Extreme Environments

β-1，4-木聚糖是具有β-1，4-连接的吡喃木糖单元骨架的异质多糖。木聚糖酶催化木聚糖水解为低聚木糖和木糖。本课题组从土壤中分离到一株嗜碱芽孢杆菌41 M-1。菌株41 M-1分泌一种新型碱性木聚糖酶，其最适pH为碱性。本研究的目的是阐明木聚糖在碱性条件下的水解机制，并设计酶分子以获得更极端的特性，如嗜碱性。首席研究员从菌株41 M-1中克隆并测序了木聚糖酶基因。推导的氨基酸序列表明，木聚糖酶由一个N-末端催化结构域和一个额外的功能未知的多肽区在C-末端。催化结构域中的Glu-93和Glu-183以及Trp-18、Trp-86、Tyr-84和Tyr-95参与催化作用。此外，木聚糖酶的C-末端区域被证明是多糖结合结构域。

beta-1,4-Xylans are heterogeneous polysaccharides that have a backbone of beta-1,4-linked xylopyranose units. Xylanases catalyze the hydrolysis of xylan to xylooligosaccharides and xylose. Recently, The head investigator has isolated alkaliphilic Bacillus sp.strain 41M-1 from soil. Strain 41M-1 secreted a novel alkaline xylanase that had an alkaline pH optimum. The objective of this study is to elucidate the mechanism of xylan hydrolysis in alkaline conditions and to engineer the enzyme molecules for more extremophilic properties, such as alkaliphily. The head investigator cloned and sequenced the xylanase gene from strain 41M-1. The deduced amino acid sequence revealed that the xylanase consisted of an N-terminal catalytic domain and an additional functionally-unknown polypeptide region at the C-terminus. Glu-93 and Glu-183 in the catalytic domain, as well as Trp-18, Trp-86, Tyr-84 and Tyr-95, were involved in catalysis. Furthermore, the C-terminal region of the xylanase proved to be a polysaccharide-binding domain.