Abstract
A novel expansin-like protein (CxEXL22) has been identified and characterized from newly isolated Arthrobotrys sp. CX1 that can cause cellulose decrystallization. Unlike previously reported expansin-like proteins from microbes, CxEXL22 has a parallel β-sheet domain at the N terminal, containing many hydrophobic residues to form the hydrophobic surface as part of the groove. The direct phylogenetic relationship implied the genetic transfers occurred from nematode to nematicidal fungal Arthrobotrys sp. CX1. CxEXL22 showed strong activity for the hydrolysis of hydrogen bonds between cellulose molecules, especially when highly crystalline cellulose was used as substrate. The hydrolysis efficiency of Avicel was increased 7.9-fold after pretreating with CxEXL22. The rupture characterization of crystalline region indicated that CxEXL22 strongly binds cellulose and breaks up hydrogen bonds in the crystalline regions of cellulose to split cellulose chains, causing significant depolymerization to expose much more microfibrils and enhances cellulose accessibility.
Highlights
Cellulose is a polymer consisting of glucose line linked by β-1,4 bonds and contains crystalline region and amorphous region
CX1 was isolated from a soil sample with rotted wood collected from the campus of Dalian Polytechnic University, China, which can disrupt cellulose chains to make the filter paper translucent (Lan et al 2016)
CX1, one sequence was termed “CxEXL22”, which encoded a protein of 193 amino acid residues, containing the low complexity region and the DPBB region, as predicted using the SMART server (Letunic et al 2021) (Fig. 1A)
Summary
Cellulose is a polymer consisting of glucose line linked by β-1,4 bonds and contains crystalline region and amorphous region. The conversion of cellulose into fuel is still limited because of its physical properties, especially the degree of polymerization, crystallinity and accessibility (Arantes and Saddler 2010; Wilson 2009). The intermolecular and intramolecular hydrogen bonds tightly packed cellulose. Ionic liquid and traditional organic solvents have been used in cellulose decrystallization and depolymerization. Their application is limited by their environmental hazard, recovery problem and high cost (Rinaldi et al 2008; Tadesse and Luque 2011; Chen et al 2015). Enzymatic degradation is an environmental-friendly process of accessing and binding the cellulose chain
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