Two degradation strategies for overcoming the recalcitrance of natural lignocellulosic xylan by polysaccharides‐binding GH10 and GH11 xylanases of filamentous fungi

Abstract

The recalcitrance of lignocellulose forms a strong barrier for the bioconversion of lignocellulosic biomass in chemical or biofuel industries. Filamentous fungi are major plant biomass decomposer, and capable of forming all the required enzymes. Here, they characterized the GH10 and GH11 endo-xylanases and a CE1 acetyl-xylan esterase (Axe1) from a superior biomass-degrading strain, Aspergillus fumigatus Z5, and examined how they interact in xylan degradation. Cellulose-binding (CBM1) domain inhibited GH10 xylanase activities for pure xylan, but afforded them an ability to hydrolyze washed corncob particles (WCCP). CBM1-containing GH10 xylanases also showed synergism with CBM1-containing Axe1 in WCCP hydrolysis, and this synergy was strictly dependent on the presence of their CBM1 domains. In contrast, GH11 xylanases had no CBM1, but still could bind xylan and hydrolyzed WCCP; however, no synergism displayed with Axe1. GH10 xylanases and GH11 xylanases showed a pronounced synergism in WCCP hydrolysis, which was dependent on the presence of the CBM1 in GH10 xylanases and absence from GH11 xylanases. They exhibit different mechanisms to bind to cellulose and xylan, and act in synergy when these two structures are intact. These findings will be helpful for the further development of highly efficient enzyme mixtures for lignocellulosic biomass conversion.

Effect of CBM1 and linker region on enzymatic properties of a novel thermostable dimeric GH10 xylanase (Xyn10A) from filamentous fungus Aspergillus fumigatus Z5

“…Although we cannot give that the interactions between CBM1/linker and hydrolase domain affected the thermostability of Xyn10A, it’s quite possible. Our previous result (Miao et al 2017 ) showed that remove of CBM1 domain or together with linker region both significantly increased the xylanase activity of Xyn10A, indicating that the interference of CBM1 and linker to hydrolase domain actually existed. When the hydrolase domain is not protected by the linker region, it will be more prone for unfolding by high temperature.…”

“…CBM1 domain has a function of cellulose-binding (Boraston et al 2004 ). With the help of CBM1, Xyn10A could get close to lignocellulosic biomass and bind the crystalline cellulose inside to degrade xylan around (Miao et al 2017 ). From this aspect, CBM1 domain and linker region should play an important role during the effect on Xyn10A’s stability through the interactions of the basic amino acid chains or 3D structures, and the fact is that removal of CBM1 and linker from Xyn10A do decrease its ability to resist high temperature (> 70 °C).…”

“…Badino et al ( 2017 ) reported that different linker modifications could change the catalytic activity and cellulose affinity of cellobiohydrolase Cel7A from Hypocrea jecorina when hydrolyzing crystalline cellulose, which showed the possibility that the glycosylated linker region joined in affinity to substrate and further affect enzymes’ catalytic activities. However, in degradation of pure xylan, CBM1 do not have a specific-binding substrate (Miao et al 2017 ), so the whole tension structure above would not exist. Protein simulation did not show a stable structure of Xyn10A that might support the possibility that CBM1 and linker would directly form a strong interaction with hydrolase domain to help its stabilizing if without substrate for binding.…”

Grazing-induced microbiome alterations drive soil organic carbon turnover and productivity in meadow steppe

“…The distinctive relationships between SOC-decomposing enzyme activity and microbial abundance revealed that fungi are more important in recalcitrant-SOC turnover while bacteria are more important in labile-SOC turnover. For instance, fungi are more efficient at decomposing lignocellulose than bacteria [ 60 ]. Moreover, more copiotrophic bacteria contain more labile-SOC-decomposing genes [ 61 ], which promotes labile-SOC turnover.…”

Proteomic analysis reflects an environmental alkalinization-coupled pH-dependent mechanism of regulating lignocellulases in Trichoderma guizhouense NJAU4742

“…Logically, the adjustment is to achieve the optimal synergy of extracellular enzymes under different pH conditions, which possibly could be explained from the different enzymatic properties of cellulases and hemicellulases. And, it is really the fact that cellulases and xylanases from the same filamentous fungus have different enzymatic properties, such as thermostability, optimal temperature, specific activity and functional domains [38]. Just like extracellular proteases, they were distinguished as acidic, neutral and alkaline proteases and regulated by the PacC-mediated system [39].…”