Introduction
Currently used chemical and mechanical treatments for cellulose activation
Alkali-treatments
Acidic treatments
Steam explosion
Mechanical treatments
Biochemical treatments for cellulose activation
Enzymatic treatments
Expansin-related proteins for lignocellulose processing and activation
Classification of expansin-related proteins
Functional characterization of expansin-related proteins on cellulosic materials
Technique | Principle | References |
---|---|---|
Biomechanical assay | Measures wet tensile strength (breaking force) of solid substrates (e.g., filter paper) after incubation with an expansin-related protein | |
Crystallinity | Measures impacts of expansin related proteins on cellulose crystallinity | |
Hydrogen bonding intensity | Measures changes in cellulose intra- and inter-chain H-bonds | |
Carbohydrate binding module adsorption | Uses CBMs with preferential binding towards crystalline versus amorphous cellulose to identify regions in cellulose fiber affected by expansion treatment. Quantifies the adsorbed amount which depends on the available surface area and accessibility | |
Brunauer–Emmett–Teller (BET) surface area analysis | Measures the change in surface area by nitrogen adsorption | (Duan et al. 2018) |
Microscopy (light, scanning electron, atomic force), laser diffraction | Estimates fiber disaggregation or morphological changes | |
Synergy with enzymes releasing soluble sugars | Measures the enzymatic release of reducing sugars in the presence of expansin-related proteins | reviewed in (Liu et al. 2015) |
Rheometry | Measures the visco-elastic behavior of cellulosic materials after treatment with expansin-related proteins | (Monschein et al. 2023) |
Binding to lignocellulose components
Substrate | Protein | Binding capacity Bmax µmol/g | Temperature, pH, buffer | Reference |
---|---|---|---|---|
Filter paper Whatman no.1 | Recombinant swollenin | 0.089 | 45 °C, pH 4.8, 50 mM sodium acetate | (Jäger et al. 2011) |
Avicel PH101 | SWO1 | 2.11 | 25 °C, pH 5.0, 50 mM sodium acetate | (Eibinger et al. 2016) |
BsEXLX1 | 0.34 | 25 °C pH 7.5, 25 mM HEPES | (Georgelis et al. 2011) | |
BsEXLX1 | 0.11 | 4 °C, pH 7.0, 50 mM potassium phosphate | (Kim et al. 2013a) | |
HcEXLX2 | 0.14 | 4 °C, pH 7.0, 100 mM sodium citrate | (Lee et al. 2013) | |
PcExl1 | 0.33 | 25 °C pH 7.5 phosphate buffer | (Olarte-Lozano et al. 2014) | |
BpEX | 0.023 | 4 °C, pH 5.0, 50 mM sodium acetate | (Bunterngsook et al. 2015) | |
CmEX | 0.024 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
SaEX | 0.032 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
PcEX | 0.05 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
MaEX | 0.038 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
PASC | BpEX | 0.501 | 4 °C, pH 5.0, 50 mM sodium acetate | (Bunterngsook et al. 2015) |
CmEX | 0.59 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
SaEX | 0.335 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
PcEX | 0.134 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
MaEX | 0.251 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
Xylan oat spelts | HcEXLX2 | 0.12 | 4 °C, pH 7.0, 100 mM sodium citrate | (Lee et al. 2010) |
Xylan birchwood | SWO1 | 22.3 | 25 °C, pH 5.0, 50 mM sodium acetate | (Eibinger et al. 2016) |
Arabinoxylan | BsEXLX1 | 3.3 | 25 °C pH 7.5, 25 mM HEPES | (Georgelis et al. 2011) |
BpEX | 0.316 | 4 °C, pH 5.0, 50 mM sodium acetate | (Bunterngsook et al. 2015) | |
CmEX | 0.354 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
SaEX | 0.164 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
PcEX | 0.03 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
MaEX | 0.091 | 4 °C, pH 5.0, 50 mM sodium acetate | ||
Lignin | SWO1 | 25.1 | 25 °C, pH 5.0, 50 mM sodium acetate | (Eibinger et al. 2016) |
Impact on cellulose fiber arrangement
Impact on the mechanical properties of cellulosic materials
Impact on the biochemical processing of cellulosic materials
Impact of operational conditions on the performance of expansin-related proteins
Substrate type | Protein | T, t, pH (EXPN) | Protein (EXPN) dose mg/g | Substrate amount w/v % | Measurement | Impact | References |
---|---|---|---|---|---|---|---|
Avicel (PH 101), Filter paper Whatman 603 | AfSwo1 | 40 °C, 72 h, 5.0 | 0–2 | 0.3 | Synergistic action with Celluclast 1.5L plus Novozymes 188 | Boost by up to 20% | (Chen et al. 2010) |
Avicel (PH 101), α-cellulose, Whatman filter paper No.1, Sigmacell 101 | Recombinant Swollenin (SWO1) | 45 °C, 2–48 h, 4.8 | 20 | 2.0 | Laser diffraction, Light microscopy, Scanning electron microscopy, X-ray diffraction | Deagglomeration of filter paper pieces, decreasing crystallinity index of cellulosic samples excluding Sigmacell No synergy with T. reesei cellulases in the hydrolysis of the different celluloses | (Jäger et al. 2011) |
Avicel (PH 101) | r-TasSWO | 50 °C 0.5–6 h 5.0 | 0.8 | 2.0 | Synergistic action with a recombinant endoglucanase (FnCel5A) | No detectable activity to low activity | (Wang et al. 2011) |
Avicel (PH 101) | Swollenin (SWO2) | 40 °C, 48 h, 4.8 | nd | 5 | X-ray diffraction. Synergistic action with a commercial cellulase (0.08–09 FPU/ g substrate) | Slight increase in crystallinity of Avicel. Boost of hydrolysis by up to 25% | (Zhou et al. 2011) |
Avicel (PH 101) | Poswo1 | 50 °C, 48 h, 4.8 | 4 | 1 | Light microscopy. Synergism with cellulase cocktail (0.8 FPU U/ g substrate) after expansin pre-treatment | Disrupting activity on Avicel. Boost of hydrolysis by up to 100% | (Kang et al. 2013) |
Avicel, Filter paper Whatman No1, Xylan from beechwood | PcExl1, BsEXLX1 | 30 °C 1–48 h | 36 | 0.4 | Biomechanical assay. Synergistic action with endo-1,4 xylanase from Trichoderma longibrachiatum (100 µg/g) or cellulase from Trichoderma reesei (0.25 U) | Filter paper weakening effect. Cellulase and xylanase activity is not influenced by the presence of PcExl1 | (Olarte-Lozano et al. 2014) |
Avicel (PH 101), PASC, arabinoxylan from wheat flour | BpEX, CmEX, SaEX, PcEX, MaEX | 50 °C, 12–48 h, 5.0 | 0.1 | 1 | Synergistic action with Celluclast 1.5L (0.06 FPU/ g substrate) | Boost by up to 400% | (Bunterngsook et al. 2015) |
Avicel (PH 101), cotton cellulose | Cms | 37 °C, 12 h, 7.0 | 0.05 | 2 | Fourier-Transform Infra-Red, Nuclear Magnetic Resonance, field emission scanning electron microscopy. Synergism with Novozymes NS2207 cellulase (2 FPU U/g substrate) after expansin pre-treatment of Avicel | Reduction in crystallinity and increased swelling of cotton. Boost of hydrolysis by 1.58 times | (Haque et al. 2015) |
Avicel (PH 101), Mercerized cotton fibers | ScExlx1 | 50 °C, 3 h, 5.0 | 20 | 0.1 | Light microscopy. Synergism with cellulase cocktail (250 U/g substrate) after expansin pre-treatment | Reduction in Avicel flocculation. Boost of hydrolysis of mercerized cotton by 60% | (Tovar-Herrera et al. 2015)) |
Avicel (PH 101), Xylan from birchwood, Dactylis glomerata grass | Swollenin (SWO1) | 40 °C, 24–72 h, 5.0 | 0.1 4 nmol/ g | 0.5 | Atomic Force Microscopy, Wide Angle X-ray Spectroscopy. Synergistic action with T. reesei cellulase (2 mg/g substrate) | No effects on crystallinity or swelling of substrates. Boost by 1.5 times | (Eibinger et al. 2016) |
Avicel (PH 101), cellulose film | BsEXLX1 | 45 °C, 72 h, 4.8 | nd | nd | X-Ray Diffraction, Brunauer-Emmet-Teller Analyzer, Fourier-Transform Infra-Red, Nuclear Magnetic Resonance | Reduction in crystallinity and increase in surface area of Avicel. Increased roughness and hydrophilicity of cellulose film | (Duan et al. 2018) |
Cellulose nanofiber | PcaLOOLs | 23 °C, 24 h, 5.0 | 40 | 0.6 | Rheological measurements | Reduced yield strain | (Monschein et al. 2023) |
Crystalline cellulose (Merck: 102,331) | OsEXPA33, OsEXPB8, OsEXLA3 | 50 °C, 24 h, 5.0 | 0.6 | 0.8 | Synergistic action with commercial cellulose from Trichoderma viride (0.06 mg/g substrate) | Boost by up to 2 times | (Seki et al. 2015) |
Dissolving hardwood pulp | Swollenin (SWO1) | 50 °C, overnight, 5.0 | 50 | 0.13 | Confocal microscopy using fluorescently labeled CBMs | Fragmentation of dissolving pulp fibers | (Gourlay et al. 2015) |
Filter paper Whatman no. 3 mercerized cotton, valonia cell wall fragments | Swollenin (SWO1) | 45 °C, 48 h, 5.0 | 10–100 | nd | Light microscopy, Biomechanical assay | Fiber swelling, filter paper weakening | (Saloheimo et al. 2002) |
Filter paper Whatman No. 1 | BsEXLX1 | 50 °C, 12–36 h, 4.8 | 0.3 | 2.0 | Biomechanical assay. Synergistic action with Celluclast 1.5L (0.012 FPU/g substrate) | Filter paper weakening effect, Boost of hydrolysis by 240% | (Kim et al. 2009) |
Filter paper Whatman No. 1 & No. 3 | HcEXLX2 | 50 °C, 48 h, 5.0 | 1.25 | nd | Biomechanical assay. Synergistic action with Celluclast 1.5 L (0.06 FPU/ g substrate) | Filter paper loosening effect, Boost by up to 4.6 times | (Lee et al. 2010) |
Filter paper Whatman No. 1 | BsEXLX1 | 50 °C, 36, 4.8 | 0.2 | 0.33 | Synergistic action with Celluclast 1.5 L (0.06 FPU/g substrate) | Boost by 77.4% | (Lin et al. 2013) |
Filter paper Whatman No. 1 | BsEXLX1, TrSwo1 | 50 °C, 18 h, 4.8 | 1.0 | 2.5 | Synergistic action with endoglucanase (8 U/g substrate) | Boost by up 95–125% respectively | (Wang et al. 2014) |
Filter paper Whatman No. 1 | LeEXP2 | 30–70 °C, 18 h, 4.8 | 1.25 | 2.5 | Biomechanical assay. Synergistic action with endoglucanase (8 U/g substrate) | Filter paper weakening effect. Boost of hydrolysis by up 75% | (Liu et al. 2014) |
Mercerized cotton Mercerized Agave tequilana fibers | LOOS1 | 25 °C 8 h, 5.0 | 0.8, 2.8–5.7 | 0.7, 2.5 | Phase-contrast microscopy Synergistic action with commercial cellulase/ xylanase cocktail (40 U endoglucanase/g substrate) | Cotton fiber swelling by ballooning Boost of hydrolysis by up to 7 times | (Quiroz-Castañeda et al. 2011) |
Mercerized cotton | Swollenin (SWO1) | 50 °C, 12 h 5.0 | 10 | nd | Differential binding of carbohydrate binding modules (CBMs) from families CBM2a and CBM44 | Increase in accessibility of carbohydrate-biding molecules | (Gourlay et al. 2012) |
Sigmacell 20, dilute acid pretreated yellow poplar | Zea m1 isoform D | 40 °C, 0–168 h, 5.0 | 0.1–3 | nd | Synergistic action with T. reesei cellulase mixture (5 FPU/g substrate) | Slight boost, dependent on time and cellulase | (Baker et al. 2000) |
Steam pretreated stover | Swollenin (SWO1) | T: nd, t: nd, pH 5.0 | 10 | 1 | Synergistic action with xylanase Xyn10 and Xyn 11 (12 mg/g substrate) | Boost by 300% | (Gourlay et al. 2013) |
Xylan from oat spelts | HcEXLX2 | 50 °C, 36 h, 7.0 | 0.16 | 0.2 | Synergistic action with recombinant xylanase (Xyn10C) (0.06 mg/g substrate) | Boost by 3 times | (Lee et al. 2013) |