Molecular Anatomy of Polysaccharide-degrading Enzymes from Extremophiles

在极端的温度、pH值和盐度等不寻常的环境中发现了许多微生物。这些微生物被称为“极端微生物”，包括嗜热菌、嗜冷菌、嗜酸菌、嗜碱菌和嗜盐菌。“极端酶”是由极端微生物产生的酶，能够在极端条件下发挥作用。极端酶具有巨大的工业应用潜力和学术方向。半纤维素是植物细胞壁中含量最丰富的多糖之一，原称用稀碱从植物细胞壁中提取的部分。-1,4-木聚糖是半纤维素的主要成分；它约占木材总干重的10%至30%。木聚糖是一种多相多糖，由-1,4-连接的木吡喃糖单元组成，其分支含有乙酰基、l -阿拉伯糖-呋喃基和葡萄糖吡喃基残基。木聚糖酶（1,4- β - d -木聚糖木聚糖水解酶；EC 3.2.1.8）催化木聚糖水解成低聚木糖和木糖。嗜碱芽孢杆菌菌株41M-1分泌的木聚糖酶（木聚糖酶J）具有碱性pH的最佳。木聚糖酶J是一种多结构域酶，由一个家族11/G催化结构域和一个木聚糖结合结构域组成。突变分析显示一些氨基酸残基对木聚糖酶J的催化活性、碱度和木聚糖结合活性有影响。

Many microorganisms have been discovered at unusual environments such as extreme temperature, pH and salinity. These microorganisms are called "extremophiles" that include thermophiles, psychrophiles, acidophiles, alkaliphiles and halophiles. "Extremozymes" are the enzymes produced by extremophiles and able to function under the extreme conditions. Extremozymes have tremendous potential for industrial applications as well as academic directions. Hemicellulose, originally named for the fraction extracted from plant cell walls with dilute alkali, is one of the most abundant polysaccharide in plant cell walls. Beta-1,4-Xylan is the major component of hemicelluloses ; it accounts for approximately 10 to 30% of the total dry weight of wood. Xylan is a heterogeneous polysaccharide comprising a backbone of beta-1,4- linked xylopyranose units with branches containing acetyl, L-arabino-furanosyl and glucopyranosyl residues. Xylanase (1,4-beta-D-xylan xylanohydrolase ; EC 3.2.1.8) catalyzes the hydrolysis of xylan to xylooligosaccharides and xylose. Alkaliphilic Bacillus sp. strain 41M-1 secretes a xylanase (xylanase J) that has an alkaline pH optimum. Xylanase J is a multidomain enzyme that consists of a family 11/G catalytic domain and a xylan-binding domain. Mutational analyzes revealed some amino acid residues that contribute to catalytic activity, alkaliphily and xylan-binding activity of xylanase J.