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首页> 外文期刊>Applied Microbiology and Biotechnology >Cloning, expression in Streptomyces lividans and biochemical characterization of a thermostable endo-beta-1,4-xylanase of Thermomonospora alba ULJB1 with cellulose-binding ability
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Cloning, expression in Streptomyces lividans and biochemical characterization of a thermostable endo-beta-1,4-xylanase of Thermomonospora alba ULJB1 with cellulose-binding ability

机译：具有纤维素结合能力的嗜热单孢藻ULJB1的热稳定内切β-1,4-木聚糖酶的克隆，在链霉菌中的表达及生化特性

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摘要

Several thermophilic actinomycetes were isolated from urban solid waste. One of them, Thermomonospora alba ULJB1, showed a broad degradative activity on xylan, cellulose, starch and other polymers. Xylanase and cellulase activities were quantified and compared with those Thermomonospora fusca. Genes encoding two different endo-beta-1,4-xylanase were cloned from T. alba ULJB1. One of them, xylA, was sequenced, subcloned and overexpressed in Streptomyces lividans. It encodes a protein of 482 amino acids with a deduced molecular mass of 48,456 Da. The protein contains a 38-amino-acid leader peptide with six Arg+ residues in its amino-terminal end, a catalytic domain and a cellulose-binding domain connected by a linker region rich in proline and glycine. The XylA protein was purified to near homogeneity from S. lividans/XylA cultures. Two forms of the extracellular xylanase, of 48 kDa and 38 kDa, were produced that differed in their cellulose-binding ability. The 48-kDa protein showed a strong binding to cellulose whereas the 38-kDa form did not bind to this polymer, apparently because of the removal during processing of the cellulose-binding domain. Both forms were able to degrade xylans form different origins but not lichenam or carboxymethylcellulose. The major degradation product was xylobiose with traces of xylose. The xylanase activity was thermostable, showing a good activity up to 95 degrees C, and had broad pH stability in the range from pH 4.0 to pH 10.0.
机译：从城市固体废物中分离出了几种嗜热放线菌。其中一种，即白热单孢菌ULJB1，对木聚糖，纤维素，淀粉和其他聚合物表现出广泛的降解活性。定量木聚糖酶和纤维素酶活性，并与热单孢菌（Thermomonospora fusca）进行比较。从T. alba ULJB1克隆了编码两种不同的内切β-1,4-木聚糖酶的基因。其中之一，xylA，已在lividans链霉菌中测序，亚克隆和过表达。它编码482个氨基酸的蛋白质，推导的分子量为48,456 Da。该蛋白质包含一个38个氨基酸的前导肽，在其氨基末端具有六个Arg +残基，一个催化域和一个纤维素结合域，该域通过富含脯氨酸和甘氨酸的连接区相连。从S. lividans / XylA培养物中将XylA蛋白纯化至接近同质。产生了两种形式的细胞外木聚糖酶，分别为48 kDa和38 kDa，它们的纤维素结合能力不同。 48-kDa蛋白显示出与纤维素的强结合，而38-kDa形式却不与该聚合物结合，这显然是因为在纤维素结合域的加工过程中将其去除了。两种形式都能够降解来自不同来源的木聚糖，但不能降解地衣木或羧甲基纤维素。主要降解产物是木糖和微量木糖。木聚糖酶活性是热稳定的，在高达95℃下显示出良好的活性，并且在pH 4.0至pH 10.0的范围内具有宽的pH稳定性。

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