Abstract
Background: Swollenins exist within some fungal species such as Trichoderma reesei and Aspergillus niger, and are candidate accessory enzymes for the biodegradation of cellulosic substrates. Swollenins theorized role in biological processes is as promoters in the rearrangement of non-covalent interaction networks formed by cell wall polysaccharides. Such network rearrangements though to be responsible for expanding accessibility for hydrolytic enzyme degradation processes. We hereby report in detail the characterization of a recombinant swollenin and its disruptive activity on cellulosic substrates and its synergistic effects while interacting with cellulases.Results: We have expressed a novel swollenin gene Tlswo consists of an open reading frame encoding 503 amino acids to be identified from Talaromyces leycettanus JCM12802 and successfully expressed it in both Trichoderma reesei and Pichia pastoris. Similar to other fungal swollenins, TlSWO is composed of a N-terminal family 1 carbohydrate binding module (CBM1) followed by a Ser/Thr rich linker connected to an expansin-like domain, followed by a family of 45 endoglucanase-like domains and a group-2 grass pollen allergen domain. From our experimental results, TlSWO demonstrated disruptive activity on Avicel and displayed a synergistic effect with cellobiohydrolases, enhancing its hydrolytic performance up to 132%. We also explored the activity of TlSWO on several model substrates as well as pretreated biomass. Our results indicate that TlSWO is capable of releasing reducing sugars from lichenan, barley β-glucan, carboxymethyl cellulose sodium (CMC-Na) and laminarin. The specific activity of TlSWO towards the substates mentioned above is 9.0 ± 0.100 U/mg, 8.9 ± 0.100U/mg, 2.3 ± 0.002 U/mg and 0.79 ± 0.002 U/mg, respectively. Moreover, further experimentation confirms the fungal swollenin TlSWO exhibits maximum activity at pH 4.0 and 50 ℃.Conclusion: This study reports on a novel swollenin protein capable of enhancing biomass conversion. Experimental data reveals the functional diversity of this swollenin with considerable activity on various substrates. Although the exact catalytic mechanism of swollenin’s remains unknown, the functional diversity of TlSWO broadens its applicability under experimental settings, and suggests it may be a promising candidate for future industrial applications.
A novel Swollenin from Talaromyces leycettanus JCM12802 enhances cellulase hydrolysis towards various substrates
