Department of Molecular Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, Luleå, Sweden.
PLoS One. 2018 Sep 5;13(9):e0203430. doi: 10.1371/journal.pone.0203430. eCollection 2018.
Our comparative studies reveal that the two lytic polysaccharide monooxygenases HiLPMO9B and HiLPMO9I from the white-rot conifer pathogen Heterobasidion irregulare display clear difference with respect to their activity against crystalline cellulose and glucomannan. HiLPMO9I produced very little soluble sugar on bacterial microcrystalline cellulose (BMCC). In contrast, HiLPMO9B was much more active against BMCC and even released more soluble sugar than the H. irregulare cellobiohydrolase I, HiCel7A. Furthermore, HiLPMO9B was shown to cooperate with and stimulate the activity of HiCel7A, both when the BMCC was first pretreated with HiLPMO9B, as well as when HiLPMO9B and HiCel7A were added together. No such stimulation was shown by HiLPMO9I. On the other hand, HiLPMO9I was shown to degrade glucomannan, using a C4-oxidizing mechanism, whereas no oxidative cleavage activity of glucomannan was detected for HiLPMO9B. Structural modeling and comparison with other glucomannan-active LPMOs suggest that conserved sugar-interacting residues on the L2, L3 and LC loops may be essential for glucomannan binding, where 4 out of 7 residues are shared by HiLPMO9I, but only one is found in HiLPMO9B. The difference shown between these two H. irregulare LPMOs may reflect distinct biological roles of these enzymes within deconstruction of different plant cell wall polysaccharides during fungal colonization of softwood.
我们的比较研究表明，白腐真菌致病疫霉的两种溶细胞多糖单加氧酶 HiLPMO9B 和 HiLPMO9I 在活性方面存在明显差异，分别针对结晶纤维素和葡甘露聚糖。HiLPMO9I 在细菌微晶纤维素（BMCC）上产生的可溶性糖很少。相比之下，HiLPMO9B 对 BMCC 的活性更高，甚至比致病疫霉的纤维二糖水解酶 I（HiCel7A）释放出更多的可溶性糖。此外，当首先用 HiLPMO9B 预处理 BMCC 时，以及当同时添加 HiLPMO9B 和 HiCel7A 时，HiLPMO9B 被证明可以与 HiCel7A 相互作用并刺激其活性。HiLPMO9I 则没有表现出这种刺激作用。另一方面，HiLPMO9I 被证明可以通过 C4 氧化机制降解葡甘露聚糖，而 HiLPMO9B 则没有检测到对葡甘露聚糖的氧化裂解活性。结构建模和与其他葡甘露聚糖活性 LPMO 的比较表明，L2、L3 和 LC 环上保守的糖相互作用残基可能对葡甘露聚糖结合至关重要，其中 HiLPMO9I 中有 7 个残基中的 4 个与之共享，但 HiLPMO9B 中只有一个。这两种 H. irregulare LPMO 之间显示的差异可能反映了这些酶在真菌定殖软木时对不同植物细胞壁多糖进行解构过程中的不同生物学作用。
