Ng Choong Hey, He Jianzhong, Yang Kun-Lin
Department of Chemical and Biomolecular Engineering, National University of Singapore, Block E5 #02-09, 4 Engineering Drive 4, Singapore, 117585, Singapore.
Appl Biochem Biotechnol. 2015 Mar;175(6):2832-44. doi: 10.1007/s12010-014-1470-5. Epub 2015 Jan 7.
Most biobutanol-producing Clostridium strains are unable to ferment polysaccharides such as cellulose and xylan due to the lack of hydrolyzing enzymes. In this study, we show that Clostridium beijerinckii G117, a newly isolated biobutanol-producing strain, expresses xylanase enzyme in the presence of 1% beechwood xylan. The xylanase activity in the medium containing actively growing culture and 1% of beechwood xylan can reach up to 2.66 U/ml after 14 h of fermentation. Using salting-out and size-exclusion chromatography, we purify the crude xylanase by 8.7-fold from the supernatant with a yield of 32.2%. This purified xylanase has a molecular weight of 22.6 kDa, making it one of the smallest reported clostridial xylanases. Conserved domain analysis reveals that the xylanase belongs to glycoside hydrolase family 11 (GH11) but lacks a carbohydrate binding domain. When beechwood xylan is used as substrate for the xylanase, majority of the products are xylo-oligosaccharide (~98%), suggesting that this is an endo-1,4-β-xylanase.
大多数产生物丁醇的梭菌菌株由于缺乏水解酶，无法发酵纤维素和木聚糖等多糖。在本研究中，我们发现新分离的产生物丁醇菌株拜氏梭菌G117在1%山毛榉木聚糖存在的情况下表达木聚糖酶。在含有活跃生长培养物和1%山毛榉木聚糖的培养基中，发酵14小时后木聚糖酶活性可达2.66 U/ml。通过盐析和尺寸排阻色谱法，我们从上清液中纯化粗木聚糖酶，纯化倍数为8.7倍，产率为32.2%。这种纯化的木聚糖酶分子量为22.6 kDa，是已报道的最小的梭菌木聚糖酶之一。保守结构域分析表明，该木聚糖酶属于糖苷水解酶家族11（GH11），但缺乏碳水化合物结合结构域。当以山毛榉木聚糖为木聚糖酶的底物时，大部分产物是木寡糖（约98%），这表明这是一种内切-1,4-β-木聚糖酶。
