Valenzuela Susana V, Lopez Sergi, Biely Peter, Sanz-Aparicio Julia, Pastor F I Javier
Department of Genetics, Microbiology and Statistics, Faculty of Biology, University of Barcelona, Barcelona, Spain IN2UB Institute of Nanoscience and Nanotechnology, University of Barcelona, Barcelona, Spain
Department of Genetics, Microbiology and Statistics, Faculty of Biology, University of Barcelona, Barcelona, Spain.
Appl Environ Microbiol. 2016 Aug 15;82(17):5116-24. doi: 10.1128/AEM.01329-16. Print 2016 Sep 1.
A GH8 family enzyme involved in xylan depolymerization has been characterized. The enzyme, Rex8A, is a reducing-end xylose-releasing exo-oligoxylanase (Rex) that efficiently hydrolyzes xylooligosaccharides and shows minor activity on polymeric xylan. Rex8A hydrolyzes xylooligomers of 3 to 6 xylose units to xylose and xylobiose in long-term incubations. Kinetic constants of Rex8A were determined on xylotriose, showing a Km of 1.64 ± 0.03 mM and a kcat value of 118.8 s(-1) Besides linear xylooligosaccharides, the enzyme hydrolyzed decorated xylooligomers. The catalytic activity on branched xylooligosaccharides, i.e., the release of xylose from the reducing end, is a newly described trait of xylose-releasing exo-oligoxylanases, as the exo-activity on these substrates has not been reported for the few of these enzymes characterized to date. Modeling of the three-dimensional (3D) structure of Rex8A shows an (α/α)6 barrel fold where the loops connecting the α-helices contour the active site. These loops, which show high sequence diversity among GH8 enzymes, shape a catalytic cleft with a -2 subsite that can accommodate methyl-glucuronic acid decorations. The hydrolytic ability of Rex8A on branched oligomers can be crucial for the complete depolymerization of highly substituted xylans, which is indispensable to accomplish biomass deconstruction and to generate efficient catalysts.
A GH8 family enzyme involved in xylan depolymerization has been characterized. The Rex8A enzyme from Paenibacillus barcinonensis is involved in depolymerization of glucuronoxylan, a major component of the lignocellulosic substrates. The study shows that Rex8A is a reducing-end xylose-releasing exo-oligoxylanase that efficiently hydrolyzes xylose from neutral and acidic xylooligosaccharides generated by the action of other xylanases also secreted by the strain. The activity of a Rex enzyme on branched xylooligosaccharides has not been described to date. This report provides original and useful information on the properties of a new example of the rarely studied Rex enzymes. Depolymerization of highly substituted xylans is crucial for biomass valorization as a platform for generation of biofuels, chemicals, and solvents.
一种参与木聚糖解聚的GH8家族酶已得到表征。该酶Rex8A是一种还原端释放木糖的外切低聚木聚糖酶（Rex），能有效水解低聚木糖，对聚合木聚糖的活性较弱。长期孵育时，Rex8A可将含有3至6个木糖单元的木寡糖水解为木糖和木二糖。测定了Rex8A对木三糖的动力学常数，其Km值为1.64±0.03 mM，kcat值为118.8 s(-1)。除了线性低聚木糖外，该酶还能水解修饰的低聚木糖。对支链低聚木糖的催化活性，即从还原端释放木糖，是释放木糖的外切低聚木聚糖酶新描述的特性，因为迄今为止对少数已表征的此类酶尚未报道其对这些底物的外切活性。Rex8A三维（3D）结构的建模显示为（α/α）6桶状折叠，连接α螺旋的环勾勒出活性位点。这些环在GH8酶之间显示出高度的序列多样性，形成了一个带有 -2亚位点的催化裂缝，可容纳甲基葡萄糖醛酸修饰。Rex8A对支链低聚物的水解能力对于高度取代木聚糖的完全解聚可能至关重要，这对于实现生物质解构和生成高效催化剂不可或缺。
一种参与木聚糖解聚的GH8家族酶已得到表征。来自巴辛诺内斯芽孢杆菌的Rex8A酶参与葡糖醛酸木聚糖的解聚，葡糖醛酸木聚糖是木质纤维素底物的主要成分。该研究表明，Rex8A是一种还原端释放木糖的外切低聚木聚糖酶，能有效从该菌株分泌的其他木聚糖酶作用产生的中性和酸性低聚木糖中水解木糖。迄今为止，尚未描述Rex酶对支链低聚木糖的活性。本报告提供了关于罕见的Rex酶新实例特性的原始且有用的信息。高度取代木聚糖的解聚对于生物质作为生物燃料、化学品和溶剂生成平台的价值化至关重要。
