AA16, a new lytic polysaccharide monooxygenase family identified in fungal secretomes

Senta Heiss-Blanquet,Sacha Grisel,Isabelle Herpoël-Gimbert,Mathieu Fanuel,Jean-Guy Berrin,Camille Filiatrault-Chastel,Didier Chevret,Mireille Haon,David Navarro,Bernard Henrissat,Antoine Margeot

doi:10.1186/s13068-019-1394-y

Abstract

BackgroundLignocellulosic biomass is considered as a promising alternative to fossil resources for the production of fuels, materials and chemicals. Efficient enzymatic systems are needed to degrade the plant cell wall and overcome its recalcitrance. A widely used producer of cellulolytic cocktails is the ascomycete Trichoderma reesei, but this organism secretes a limited set of enzymes. To improve the saccharification yields, one strategy is to upgrade the T. reesei enzyme cocktail with enzymes produced by other biomass-degrading filamentous fungi isolated from biodiversity.ResultsIn this study, the enzymatic cocktails secreted by five strains from the genus Aspergillus (Aspergillus japonicus strains BRFM 405, 1487, 1489, 1490 and Aspergillus niger strain BRFM 430) were tested for their ability to boost a T. reesei reference cocktail for the saccharification of pretreated biomass. Proteomic analysis of fungal secretomes that significantly improved biomass degradation showed that the presence of proteins belonging to a putative LPMO family previously identified by genome analysis and awaiting experimental demonstration of activity. Members of this novel LPMO family, named AA16, are encountered in fungi and oomycetes with life styles oriented toward interactions with plant biomass. One AA16 protein from Aspergillus aculeatus (AaAA16) was produced to high level in Pichia pastoris. LPMO-type enzyme activity was demonstrated on cellulose with oxidative cleavage at the C1 position of the glucose unit. AaAA16 LPMO was found to significantly improve the activity of T. reesei CBHI on cellulosic substrates.ConclusionsAlthough Aspergillus spp. has been investigated for decades for their CAZymes diversity, we identified members of a new fungal LPMO family using secretomics and functional assays. Properties of the founding member of the AA16 family characterized herein could be of interest for use in biorefineries.

Highlights

Lignocellulosic biomass is considered as a promising alternative to fossil resources for the production of fuels, materials and chemicals
After 48 h of biomass saccharification, three secretomes were able to significantly improve the cellulose conversion yield of wheat straw (Fig. 1a), which is noteworthy given that the yields using the reference cocktail alone were already high, reaching 60% glucose release from cellulose after only 24 h, and over 90% at the plateau (Additional file 1: Figure S1)
As for the two remaining strains (A. japonicus BRFM 1487 and 1490), their secretomes produced on lignocellulosic substrates (MB and sugar beet pulp (SBP)) improved the glucose yield by 9 to 16%, while their secretomes produced on Avicel did not lead to any significant improvement

Summary

Introduction

Lignocellulosic biomass is considered as a promising alternative to fossil resources for the production of fuels, materials and chemicals. Lignocellulosic biomass is a renewable and abundant feedstock, considered as a promising alternative to nonsustainable fossil resources for the production of biofuels, biomaterials and bio-based chemicals [1, 2]. The degradation of plant polysaccharides into simple sugars can be achieved using enzymes secreted by biomass-degrading organisms such as bacteria and filamentous fungi. These carbohydrate-active enzymes (or CAZymes) are classified in the CAZy database (http:// www.cazy.org/) into several families based on their amino acid sequence similarities [3]. All LPMOs share some common features, such as a copper-containing active site, in which the metal is coordinated by three nitrogen atoms from two histidine side chains and the N-terminal amine group that form the socalled “histidine brace” [9, 10]

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Conclusion