Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Ås, Norway.
Group Bioprocess Engineering, Fraunhofer Institute of Interfacial Engineering and Biotechnology, 70569 Stuttgart, Germany.
Proc Natl Acad Sci U S A. 2022 Aug 23;119(34):e2204510119. doi: 10.1073/pnas.2204510119. Epub 2022 Aug 15.
Lytic polysaccharide monooxygenases (LPMOs) catalyze oxidative cleavage of crystalline polysaccharides such as cellulose and chitin and are important for biomass conversion in the biosphere as well as in biorefineries. The target polysaccharides of LPMOs naturally occur in copolymeric structures such as plant cell walls and insect cuticles that are rich in phenolic compounds, which contribute rigidity and stiffness to these materials. Since these phenolics may be photoactive and since LPMO action depends on reducing equivalents, we hypothesized that LPMOs may enable light-driven biomass conversion. Here, we show that redox compounds naturally present in shed insect exoskeletons enable harvesting of light energy to drive LPMO reactions and thus biomass conversion. The primary underlying mechanism is that irradiation of exoskeletons with visible light leads to the generation of HO, which fuels LPMO peroxygenase reactions. Experiments with a cellulose model substrate show that the impact of light depends on both light and exoskeleton dosage and that light-driven LPMO activity is inhibited by a competing HO-consuming enzyme. Degradation experiments with the chitin-rich exoskeletons themselves show that solubilization of chitin by a chitin-active LPMO is promoted by light. The fact that LPMO reactions, and likely reactions catalyzed by other biomass-converting redox enzymes, are fueled by light-driven abiotic reactions in nature provides an enzyme-based explanation for the known impact of visible light on biomass conversion.
溶细胞多糖单加氧酶（LPMOs）催化晶体多糖（如纤维素和几丁质）的氧化裂解，对于生物圈以及生物精炼厂中的生物质转化都非常重要。LPMOs 的目标多糖天然存在于富含酚类化合物的共聚体结构中，如植物细胞壁和昆虫外骨骼，这些酚类化合物为这些材料提供刚性和硬度。由于这些酚类化合物可能具有光活性，并且 LPMO 的作用依赖于还原当量，因此我们假设 LPMOs 可能能够实现光驱动的生物质转化。在这里，我们表明，昆虫外骨骼中天然存在的氧化还原化合物能够捕获光能以驱动 LPMO 反应，从而实现生物质转化。主要的潜在机制是，用可见光照射外骨骼会产生 HO，为 LPMO 过氧化物酶反应提供燃料。用纤维素模型底物进行的实验表明，光的影响取决于光和外骨骼的剂量，并且 HO 消耗酶会抑制光驱动的 LPMO 活性。用富含几丁质的外骨骼本身进行的降解实验表明，光驱动的非生物反应促进了由几丁质活性 LPMO 介导的几丁质的溶解。事实上，LPMO 反应，以及可能由其他生物质转化氧化还原酶催化的反应，都是由自然中光驱动的非生物反应提供燃料，这为可见光对生物质转化的已知影响提供了基于酶的解释。
