Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, P. R. China.
J Microbiol Biotechnol. 2011 Aug;21(8):861-8. doi: 10.4014/jmb.1102.02024.
A xylanase gene, xyn7c, was cloned from Paenibacillus sp. 12-11, an alkalophilic strain isolated from the alkaline wastewater sludge of a paper mill, and expressed in Escherichia coli. The full-length gene consists of 1,296 bp and encodes a mature protein of 400 residues (excluding the putative signal peptide) that belongs to the glycoside hydrolase family 10. The optimal pH of the purified recombinant XYN7C was found to be 8.0, and the enzyme had good pH adaptability at 6.5-8.5 and stability over a broad pH range of 5.0-11.0. XYN7C exhibited maximum activity at 55 degrees C and was thermostable at 50 degrees C and below. Using wheat arabinoxylan as the substrate, XYN7C had a high specific activity of 1,886 U/mg, and the apparent Km and Vmax values were 1.18 mg/ml and 1,961 μmol/mg/min, respectively. XYN7C also had substrate specificity towards various xylans, and was highly resistant to neutral proteases. The main hydrolysis products of xylans were xylose and xylobiose. These properties make XYN7C a promising candidate to be used in biobleaching, baking, and cotton scouring processes.
从碱性造纸废水污泥中分离到的嗜碱芽孢杆菌 12-11 中克隆了一个木聚糖酶基因 xyn7c，并在大肠杆菌中表达。全长基因由 1296bp 组成，编码一个由 400 个残基（不包括假定的信号肽）组成的成熟蛋白，属于糖苷水解酶家族 10。纯化的重组 XYN7C 的最适 pH 值为 8.0，该酶在 6.5-8.5 的 pH 值范围内具有良好的 pH 适应性和在 pH5.0-11.0 范围内的广泛稳定性。在 55°C 下，XYN7C 表现出最大活性，在 50°C 及以下温度下具有热稳定性。以小麦阿拉伯木聚糖为底物时，XYN7C 的比活高达 1886U/mg，表观 Km 和 Vmax 值分别为 1.18mg/ml 和 1961μmol/mg/min。XYN7C 对各种木聚糖也具有底物特异性，并且对中性蛋白酶具有高度抗性。木聚糖的主要水解产物为木糖和木二糖。这些特性使 XYN7C 成为生物漂白、烘焙和棉纺织加工过程中的有前途的候选酶。
