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Influence of the carbohydrate-binding module on the activity of a fungal AA9 lytic polysaccharide monooxygenase on cellulosic substrates. | LitMetric

AI Article Synopsis

  • Lytic polysaccharide monooxygenases (LPMOs) are vital enzymes secreted by fungi that help break down tough lignocellulosic materials and have applications in producing biofuels and nanocelluloses, although their mechanism isn't fully understood.
  • This study focused on investigating the effect of a carbohydrate-binding module (CBM1) attached to LPMO9H, demonstrating that its removal reduced binding to cellulose and decreased sugar release, albeit some activity remained on soluble sugars and in synergy with other enzymes.
  • Findings suggest that while CBM1 enhances LPMO9H's efficiency and sugar release, its absence doesn't stop the enzyme's activity, indicating that CBM1 plays a crucial role in guiding the enzyme

Article Abstract

Background: Cellulose-active lytic polysaccharide monooxygenases (LPMOs) secreted by filamentous fungi play a key role in the degradation of recalcitrant lignocellulosic biomass. They can occur as multidomain proteins fused to a carbohydrate-binding module (CBM). From a biotech perspective, LPMOs are promising innovative tools for producing nanocelluloses and biofuels, but their direct action on cellulosic substrates is not fully understood.

Results: In this study, we probed the role of the CBM from family 1 (CBM1) appended to the LPMO9H from (LPMO9H) using model cellulosic substrates. Deletion of the CBM1 weakened the binding to cellulose nanofibrils, amorphous and crystalline cellulose. Although the release of soluble sugars from cellulose was drastically reduced under standard conditions, the truncated LPMO retained some activity on soluble oligosaccharides. The cellulolytic action of the truncated LPMO was demonstrated using synergy experiments with a cellobiohydrolase (CBH). The truncated LPMO was still able to improve the efficiency of the CBH on cellulose nanofibrils in the same range as the full-length LPMO. Increasing the substrate concentration enhanced the performance of LPMO9H without CBM in terms of product release. Interestingly, removing the CBM also altered the regioselectivity of LPMO9H, significantly increasing cleavage at the C1 position. Analysis of the insoluble fraction of cellulosic substrates evaluated by optical and atomic force microscopy confirmed that the CBM1 module was not strictly required to promote disruption of the cellulose network.

Conclusions: Absence of the CBM1 does not preclude the activity of the LPMO on cellulose but its presence has an important role in driving the enzyme to the substrate and releasing more soluble sugars (both oxidized and non-oxidized), thus facilitating the detection of LPMO activity at low substrate concentration. These results provide insights into the mechanism of action of fungal LPMOs on cellulose to produce nanocelluloses and biofuels.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6721207PMC
http://dx.doi.org/10.1186/s13068-019-1548-yDOI Listing

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