Department of Energy Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI, 48824, USA.
Biotechnol Biofuels. 2013 Apr 26;6(1):58. doi: 10.1186/1754-6834-6-58.
Although α-linked xylose is a major constituent of the hemicelluloses of land plants, few secreted α-xylosidases have been described from fungi or bacteria. AxlA of Aspergillus niger is a secreted α-xylosidase that was earlier shown to promote the release of free glucose (Glc) and xylose (Xyl) from substrates containing α-linked xylose, including isoprimeverose (IP), the heptasaccharide subunit of pea xyloglucan (XG), and tamarind XG.
The utility of AxlA for enhancing release of free Glc and Xyl in combination with commercial enzyme cocktails from dicotyledonous and monocotyledonous plants was examined. Without AxlA supplementation, a mixture of CTec2 and HTec2 (both of which are derived from T. reesei) did not release significant levels of Glc from pea XG or tamarind XG. This is consistent with their lack of detectable α-xylosidase activity using model substrates. On alkaline hydrogen peroxide-pretreated corn stover, supplementation of CTec2/HTec2 (at a loading of 2.5 mg/g glucan) with AxlA (at a loading of 8 mg/g glucan) increased Glc yields from 82% to 88% of the total available Glc and increased Xyl yields from 55% to 60%. AxlA supplementation also improved Glc yields from corn stover treated with the commercial cellulase Accellerase 1000. The AxlA enhancement was not a general protein effect because bovine serum albumin or bovine gamma-globulin at similar concentrations did not enhance Glc yields from corn stover in response to CTec2/HTec2. Supplementation of CTec2/HTec2 with AxlA did not enhance Glc release from pretreated green or etiolated pea tissue. However, AxlA did enhance Glc and Xyl yields compared to CTec2/HTec2 alone from another dicotyledonous herbaceous plant, Chenopodium album (lamb's quarters).
Supplementation of commercial cellulase cocktails with AxlA enhances yields of Glc and Xyl from some biomass substrates under some conditions, and may prove useful in industrial lignocellulose conversion.
尽管α-连接木糖是陆生植物半纤维素的主要成分，但从真菌或细菌中分离出的分泌型α-木糖苷酶却很少。黑曲霉的 AxlA 是一种分泌型的α-木糖苷酶，它先前被证明能够促进含有α-连接木糖的底物释放游离葡萄糖（Glc）和木糖（Xyl），包括异海藻糖（IP）、豌豆木葡聚糖的七糖亚基（XG）和罗望子 XG。
研究了 AxlA 与来自双子叶植物和单子叶植物的商业酶混合物联合使用时对提高游离 Glc 和 Xyl 释放的效果。没有 AxlA 的补充，混合物 CTec2 和 HTec2（均来自 T.reesei）没有从豌豆 XG 或罗望子 XG 中释放出显著水平的 Glc，这与它们在使用模型底物时缺乏可检测的 α-木糖苷酶活性是一致的。在经过碱性过氧化氢预处理的玉米秸秆上，当用 AxlA（用量为 8mg/g 葡聚糖）补充 CTec2/HTec2（用量为 2.5mg/g 葡聚糖）时，Glc 的收率从可利用 Glc 的 82%增加到 88%，Xyl 的收率从 55%增加到 60%。AxlA 的补充也提高了商业纤维素酶 Accellerase 1000 处理过的玉米秸秆的 Glc 收率。AxlA 的增强作用不是一般的蛋白质效应，因为牛血清白蛋白或牛γ球蛋白在类似浓度下不能在 CTec2/HTec2 作用下提高玉米秸秆的 Glc 收率。CTec2/HTec2 补充 AxlA 并没有提高预处理过的绿色或黄化豌豆组织的 Glc 释放。然而，与 CTec2/HTec2 单独使用相比，AxlA 确实提高了另一种双子叶草本植物藜（Chenopodium album）的 Glc 和 Xyl 的收率。
在某些条件下，在商业纤维素酶混合物中补充 AxlA 可以提高一些生物质底物中 Glc 和 Xyl 的产量，这在工业木质纤维素转化中可能是有用的。
