Biomass Refinery Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 3-11-32 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan.
AMB Express. 2014 Apr 1;4:27. doi: 10.1186/s13568-014-0027-x. eCollection 2014.
Cellulosic materials constitute most of the biomass on earth, and can be converted into biofuel or bio-based materials if fermentable sugars can be released using cellulose-related enzymes. Acremonium cellulolyticus is a mesophilic fungus which produces a high amount of cellulose-related enzymes. In the genome sequence data of A. cellulolyticus, ORFs showing homology to GH10 and GH11 xylanases were found. The xylanases of A. cellulolyticus play an important role in cellulolytic biomass degradation. Search of a draft genome sequence of A. cellulolyticus for xylanase coding regions identified seven ORFs showing homology to GH 11 xylanase genes (xylA, xylB, xylC, xylD, xylE, xylF and xylG). These genes were cloned and their enzymes were prepared with a homologous expression system under the control of a glucoamylase promoter. Six of the seven recombinant enzymes were successfully expressed, prepared, and characterized. These enzymes exhibited optimal xylanase activity at pH 4.0 - 4.5. But this time, we found that only XylC had enormously higher relative activity (2947 U•mg (-1)) than the other xylanases at optimum pH. This result is surprising because XylC does not retain a carbohydrate-binding module 1 (CBM-1) that is necessary to bind tightly own substrate such as xylan. In this study, we discuss the relationship between activity, pH and sequence of seven xylanases in A. cellulolyticus.
纤维素材料构成了地球上大部分的生物质，如果能利用与纤维素相关的酶释放出可发酵糖，就可以将其转化为生物燃料或生物基材料。嗜热真菌 Acremonium cellulolyticus 能产生大量与纤维素相关的酶。在 A. cellulolyticus 的基因组序列数据中，发现了与 GH10 和 GH11 木聚糖酶同源的 ORFs。A. cellulolyticus 的木聚糖酶在纤维素生物质降解中起着重要作用。在 A. cellulolyticus 的草图基因组序列中搜索木聚糖酶编码区，鉴定出 7 个与 GH11 木聚糖酶基因（xylA、xylB、xylC、xylD、xylE、xylF 和 xylG）同源的 ORFs。这些基因通过同源表达系统在葡萄糖淀粉酶启动子的控制下进行克隆，并制备其酶。其中 6 个重组酶成功表达、制备和表征。这些酶在 pH 4.0-4.5 时表现出最佳的木聚糖酶活性。但这次，我们发现只有 XylC 在最适 pH 时具有比其他木聚糖酶高得多的相对活性（2947 U·mg-1）。这一结果令人惊讶，因为 XylC 不保留碳水化合物结合模块 1（CBM-1），该模块是结合木聚糖等自身底物所必需的。在这项研究中，我们讨论了 A. cellulolyticus 中 7 种木聚糖酶的活性、pH 值和序列之间的关系。
