Pretreatment of chitin depolymerization by expansin-like protein to improve hydrolysis efficiency.

Chitin is a polysaccharide similar to cellulose that contains abundant hydrogen bonds. Expansin-like proteins disrupt hydrogen bond networks, causing cellulose to swell and accelerating its degradation. We examined the effects of pretreatment with two expansin-like proteins, CxEXL22 (Arthrobotrys sp. CX1) and HcEXL (Hahella chejuensis), on chitin depolymerisation and enzymatic degradation. The efficiency of chitin degradation increased more than two-fold after pretreatment with expansin-like proteins. Following pretreatment with expansin-like proteins, chitin had a lower crystallinity index, greater d-spacing and crystallite size, and weaker hydrogen bonds, and the loosened porous microfibrils were more exposed than in untreated chitin. The rupture characterisation of crystalline chitin indicated that expansin-like proteins loosened the hydrogen bonds of the chitin polysaccharide chains, causing significant depolymerisation to expose more porous structures and enhance chitin accessibility.

A novel decrystallizing protein CxEXL22 from Arthrobotrys sp. CX1 capable of synergistically hydrolyzing cellulose with cellulases.

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 ß-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.