Gallardo O, Diaz P, Pastor F I J
Department of Microbiology, Faculty of Biology, University of Barcelona, Avinguda Diagonal 645, 08028, Barcelona, Spain.
Appl Microbiol Biotechnol. 2003 May;61(3):226-33. doi: 10.1007/s00253-003-1239-1. Epub 2003 Feb 27.
The sequence of gene xynB encoding xylanase B from Paenibacillus sp. BP-23 was determined. It revealed an open reading frame of 999 nucleotides encoding a protein of 38,561 Da. The deduced amino acid sequence of xylanase B shows that the N-terminal region of the enzyme lacks the features of a signal peptide. When the xylan-degrading system of Paenibacillus sp. BP-23 was analysed in zymograms, it revealed that xylanase B was not secreted to the extracellular medium but instead remained cell-associated, even in late stationary-phase cultures. When xynB was expressed in a Bacillus subtilis secreting host, it also remained associated with the cells. Sequence homology analysis showed that xylanase B from Paenibacillus sp. BP-23 belongs to family 10 glycosyl hydrolases, exhibiting a distinctive high homology to six xylanases of this family. The homologous enzymes were also found to be devoid of a signal peptide and seem to constitute, together with xylanase B, a separate group of enzymes. They all have two conserved amino acid regions not found in the other family 10 xylanases, and cluster in a separate group after dendrogram analysis. We propose that these enzymes constitute a new subclass of family 10 xylanases, that are cell-associated, and that hydrolyse the xylooligosaccharides resulting from extracellular xylan hydrolysis. Xylanase B shows similar specific activity on aryl-xylosides and xylans. This can be correlated to some, not yet identified, trait of catalytic activity of the enzyme on plant xylan.
测定了来自芽孢杆菌属BP - 23的编码木聚糖酶B的基因xynB的序列。它揭示了一个999个核苷酸的开放阅读框，编码一种38,561 Da的蛋白质。推导的木聚糖酶B的氨基酸序列表明，该酶的N端区域缺乏信号肽的特征。当对芽孢杆菌属BP - 23的木聚糖降解系统进行酶谱分析时，发现木聚糖酶B没有分泌到细胞外培养基中，而是与细胞相关联，即使在生长后期的静止期培养物中也是如此。当xynB在枯草芽孢杆菌分泌宿主中表达时，它也与细胞相关联。序列同源性分析表明，芽孢杆菌属BP - 23的木聚糖酶B属于第10家族糖基水解酶，与该家族的六种木聚糖酶具有显著的高同源性。还发现同源酶缺乏信号肽，并且似乎与木聚糖酶B一起构成一组单独的酶。它们都有两个在其他第10家族木聚糖酶中未发现的保守氨基酸区域，并且在聚类分析后聚集在一个单独的组中。我们提出这些酶构成第10家族木聚糖酶的一个新亚类，它们与细胞相关联，并且水解细胞外木聚糖水解产生的木寡糖。木聚糖酶B对芳基木糖苷和木聚糖表现出相似的比活性。这可能与该酶对植物木聚糖的某些尚未确定的催化活性特征相关。
