La Grange D C, Claeyssens M, Pretorius I S, Van Zyl W H
Department of Microbiology, University of Stellenbosch, South Africa.
Appl Microbiol Biotechnol. 2000 Aug;54(2):195-200. doi: 10.1007/s002530000372.
The xynB gene encoding the Bacillus pumilus beta-xylosidase was expressed separately and jointly with the Trichoderma reesei beta-xylanase (xyn2) gene in the yeast Saccharomyces cerevisiae. Both genes were placed under the transcriptional control of the glucose-derepressible alcohol dehydrogenase 2 promoter (ADH2p) and terminator (ADH2T) sequences. The xynB gene was fused in frame to the yeast mating factor alpha1 secretion sequence (MFalpha1s) to effect secretion in S. cerevisiae. The fusion protein was designated Xlo1. Xlo1 produced in S. cerevisiae exhibited low affinity for xylobiose, but eventually hydrolyzed xylobiose and xylotriose to the monomeric constituent, D-xylose. Coproduction of Xyn2 and Xlo1 by S. cerevisiae led to a 25% increase in the amount of reducing sugars released from birchwood xylan compared to S. cerevisiae producing only the Xyn2 beta-xylanase. However, no D-xylose was produced from birchwood xylan, presumably due to very low Xlo1 beta-xylosidase activity and its low affinity for xylobiose.
编码短小芽孢杆菌β-木糖苷酶的xynB基因在酿酒酵母中单独表达，并与里氏木霉β-木聚糖酶（xyn2）基因共同表达。这两个基因都置于葡萄糖阻遏型乙醇脱氢酶2启动子（ADH2p）和终止子（ADH2T）序列的转录控制之下。xynB基因与酵母交配因子α1分泌序列（MFalpha1s）进行框内融合，以实现其在酿酒酵母中的分泌。该融合蛋白被命名为Xlo1。在酿酒酵母中产生的Xlo1对木二糖的亲和力较低，但最终能将木二糖和木三糖水解为单体成分D-木糖。与仅产生Xyn2β-木聚糖酶的酿酒酵母相比，酿酒酵母共同产生Xyn2和Xlo1可使从桦木木聚糖释放的还原糖量增加25%。然而，桦木木聚糖并未产生D-木糖，推测这是由于Xlo1β-木糖苷酶活性非常低且对木二糖的亲和力较低所致。
