Molecular mechanism of lytic polysaccharide monooxygenases.
Molecular mechanism of lytic polysaccharide monooxygenases.
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DOI：
10.1039/c8sc00426a
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发表时间：
2018-04-21
期刊：
影响因子：
8.4
通讯作者：
Ryde U
中科院分区：
文献类型：
--
作者：
Hedegård ED;Ryde U
多糖单加氧酶（LPMOs）是铜金属酶，可以通过氧化机制促进多糖解聚，从而促进纤维素等生物燃料的产生。利用量子力学和分子力学相结合的密度泛函理论（QM/MM），完整地描述了LPMOs的分子机理。多糖单加氧酶（LPMOs）是铜金属酶，可以通过氧化机制促进多糖解聚，从而促进纤维素等生物燃料的产生。利用量子力学和分子力学相结合的密度泛函理论（QM/MM），完整地描述了LPMOs的分子机理。QM/MM方案允许我们用详细的蛋白质环境描述所有反应步骤，我们证明这是必要的。以前已经提出了几种能够从底物中提取氢的活性物质，并且从最近对底物- lpmo配合物的晶体学研究开始，我们研究了以前提出的途径以及新的途径。我们描述了反应中间体的生成，从多糖底物中提取氢原子，以及OH被转移回底物的最后重组步骤。我们发现超氧[CuO2]+络合物可以被附近的组氨酸残基质子化（最近的诱变研究和晶体学工作表明），并且在提供电子源的情况下，在O-O键断裂和水解离后形成氧络合物。氧配合物与底物反应或进一步质子化成羟基配合物。氧和羟基配合物也很容易与H2O2反应生成，最近有人认为H2O2才是真正的共底物，而不是O2。氧和羟基配合物对C-H的萃取总体上是有利的，其活化势垒分别为69和94 kJ mol-1，而铜-超氧配合物的活化势垒要高得多（156 kJ mol-1）。我们得到了结构数据可用的中间体的结构一致性很好，估计的反应能与实验速率常数一致。因此，我们提出的机制是迄今为止最完整的，与现有的实验证据一致。
The lytic polysaccharide monooxygenases (LPMOs) are copper metalloenzymes that can enhance polysaccharide depolymerization through an oxidative mechanism and hence boost generation of biofuel from e.g. cellulose. By employing density functional theory in a combination of quantum mechanics and molecular mechanics (QM/MM), we report a complete description of the molecular mechanism of LPMOs. The lytic polysaccharide monooxygenases (LPMOs) are copper metalloenzymes that can enhance polysaccharide depolymerization through an oxidative mechanism and hence boost generation of biofuel from e.g. cellulose. By employing density functional theory in a combination of quantum mechanics and molecular mechanics (QM/MM), we report a complete description of the molecular mechanism of LPMOs. The QM/MM scheme allows us to describe all reaction steps with a detailed protein environment and we show that this is necessary. Several active species capable of abstracting a hydrogen from the substrate have been proposed previously and starting from recent crystallographic work on a substrate–LPMO complex, we investigate previously suggested paths as well as new ones. We describe the generation of the reactive intermediates, the abstraction of a hydrogen atom from the polysaccharide substrate, as well as the final recombination step in which OH is transferred back to the substrate. We show that a superoxo [CuO2]+ complex can be protonated by a nearby histidine residue (suggested by recent mutagenesis studies and crystallographic work) and, provided an electron source is available, leads to formation of an oxyl-complex after cleavage of the O–O bond and dissociation of water. The oxyl complex either reacts with the substrate or is further protonated to a hydroxyl complex. Both the oxyl and hydroxyl complexes are also readily generated from a reaction with H2O2, which was recently suggested to be the true co-substrate, rather than O2. The C–H abstraction by the oxyl and hydroxy complexes is overall favorable with activation barriers of 69 and 94 kJ mol–1, compared to the much higher barrier (156 kJ mol–1) obtained for the copper–superoxo species. We obtain good structural agreement for intermediates for which structural data are available and the estimated reaction energies agree with experimental rate constants. Thus, our suggested mechanism is the most complete to date and concur with available experimental evidence.