Department of Food Science and Technology, BOKU-University of Natural Resources and Life Sciences, Vienna, Austria.
Department of Chemistry, BOKU-University of Natural Resources and Life Sciences, Vienna, Austria.
Appl Environ Microbiol. 2019 Jun 17;85(13). doi: 10.1128/AEM.00390-19. Print 2019 Jul 1.
Pyranose 2-oxidase (POx) has long been accredited a physiological role in lignin degradation, but evidence to provide insights into the biochemical mechanisms and interactions is insufficient. There are ample data in the literature on the oxidase and dehydrogenase activities of POx, yet the biological relevance of this duality could not be established conclusively. Here we present a comprehensive biochemical and phylogenetic characterization of a novel pyranose 2-oxidase from the actinomycetous bacterium (POx) as well as a possible biomolecular synergism of this enzyme with peroxidases using phenolic model substrates A phylogenetic analysis of both fungal and bacterial putative POx-encoding sequences revealed their close evolutionary relationship and supports a late horizontal gene transfer of ancestral POx sequences. We successfully expressed and characterized a novel bacterial POx gene from , one of the putative POx genes closely related to well-known fungal POx genes. Its biochemical characteristics comply with most of the classical hallmarks of known fungal pyranose 2-oxidases, i.e., reactivity with a range of different monosaccharides as electron donors as well as activity with oxygen, various quinones, and complexed metal ions as electron acceptors. Thus, POx shows the pronounced duality of oxidase and dehydrogenase similar to that of fungal POx. We further performed efficient redox cycling of aromatic lignin model compounds between POx and manganese peroxidase (MnP). In addition, we found a Mn(III) reduction activity in POx, which, in combination with its ability to provide HO, implies this and potentially other POx as complementary enzymatic tools for oxidative lignin degradation by specialized peroxidases. Establishment of a mechanistic synergism between pyranose oxidase and (manganese) peroxidases represents a vital step in the course of elucidating microbial lignin degradation. Here, the comprehensive characterization of a bacterial pyranose 2-oxidase from is of particular interest for several reasons. First, the phylogenetic analysis of putative pyranose oxidase genes reveals a widespread occurrence of highly similar enzymes in bacteria. Still, there is only a single report on a bacterial pyranose oxidase, stressing the need of closing this gap in the scientific literature. In addition, the relatively small proteome supposedly supplies a limited set of enzymatic functions to realize lignocellulosic biomass degradation. Both enzyme and organism therefore present a viable model to study the mechanisms of bacterial lignin decomposition, elucidate physiologically relevant interactions with specialized peroxidases, and potentially realize biotechnological applications.
吡喃糖 2-氧化酶（POx）长期以来一直被认为在木质素降解中具有生理作用，但提供深入了解生化机制和相互作用的证据还不够充分。文献中有大量关于 POx 的氧化酶和脱氢酶活性的资料，但这种双重性的生物学相关性还不能得到明确的证实。在这里，我们介绍了一种来自放线菌的新型吡喃糖 2-氧化酶（POx）的全面生化和系统发育特征，以及该酶与过氧化物酶之间可能存在的生物分子协同作用，使用酚类模型底物。对真菌和细菌中假定的 POx 编码序列的系统发育分析表明它们具有密切的进化关系，并支持祖先 POx 序列的晚期水平基因转移。我们成功地从 中表达和表征了一种新型的细菌 POx 基因，这是与已知真菌 POx 基因密切相关的假定 POx 基因之一。其生化特性符合大多数已知真菌吡喃糖 2-氧化酶的经典特征，即与一系列不同的单糖作为电子供体反应，以及与氧气、各种醌和络合金属离子作为电子受体反应。因此，POx 表现出与真菌 POx 相似的氧化酶和脱氢酶的明显双重性。我们进一步在 POx 和锰过氧化物酶（MnP）之间进行了有效的芳香木质素模型化合物的氧化还原循环。此外，我们发现 POx 具有 Mn(III)还原活性，这与它提供 HO 的能力相结合，意味着这种 POx 以及其他潜在的 POx 是专门过氧化物酶进行氧化木质素降解的互补酶工具。建立吡喃糖氧化酶和（锰）过氧化物酶之间的机制协同作用是阐明微生物木质素降解过程中的重要步骤。在这里，来自 的细菌吡喃糖 2-氧化酶的全面表征具有特别重要的意义。首先，对假定的吡喃糖氧化酶基因的系统发育分析表明，细菌中存在广泛分布的高度相似的酶。尽管如此，关于细菌吡喃糖氧化酶的报道仅有一篇，这突出表明需要在科学文献中填补这一空白。此外，相对较小的 蛋白质组据称提供了有限的酶功能集，以实现木质纤维素生物质的降解。酶和生物体因此都成为研究细菌木质素分解机制、阐明与专门过氧化物酶的生理相关相互作用以及潜在实现生物技术应用的可行模型。
