Microbial Expansins and Cellulose Degradation Techniques

Microbial expansins are non-hydrolytic proteins found in bacteria and fungi that loosen the tightly packed cellulose microfibril network within plant cell walls. By disrupting hydrogen bonds and increasing the spacing between adjacent fibrils, these proteins enhance the accessibility of cellulolytic enzymes to their substrate without directly cleaving glycosidic bonds. Common classes include bacterial expansins (e.g. EXLX family), fungal loosenins and swollenins, and the newly described microfibril swelling proteins from various Bacillus species. In parallel, advances in cellulose degradation techniques encompass a range of physicochemical pretreatments, enzyme cocktail optimisation and oxidative auxiliary enzymes such as lytic polysaccharide monooxygenases. The synergistic integration of microbial expansins with cellulases and pretreatment regimes has emerged as a promising strategy to reduce enzyme loadings, accelerate hydrolysis rates and improve yields of fermentable sugars. Such approaches are pivotal for sustainable biorefineries, biofuel production and the generation of high-value bioproducts from lignocellulosic biomass at industrial scale.

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Microbial Expansins and Cellulose Degradation Techniques publication trend

The graph below shows the total number of articles in microbial expansins and cellulose degradation techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Microbial expansins: Non-enzymatic proteins that disrupt hydrogen bonds within cellulose microfibrils, facilitating cell-wall loosening without hydrolytic activity.

Cellulose microfibrils: Bundles of β-1,4-linked glucose chains organised into semi-crystalline fibres in plant cell-wall matrices.

Carbohydrate-binding module (CBM): Non-catalytic protein domain that recognises and attaches to specific polysaccharide surfaces, enhancing substrate proximity of catalytic partners.

Lytic polysaccharide monooxygenases (LPMOs): Copper-dependent oxidative enzymes that cleave glycosidic bonds by introducing chain breaks in recalcitrant polysaccharides.

Amorphogenesis: The non-hydrolytic ‘opening up’ or loosening of crystalline cellulose regions by proteins or pretreatments, increasing enzyme accessibility.

Interfibrillar spacing: The distance between adjacent cellulose microfibrils, a key determinant of substrate accessibility for enzymatic degradation.

References

1. Fungal loosenin-like proteins boost the cellulolytic enzyme conversion of pretreated wood fiber and cellulosic pulps. Bioresource Technology (2023).
2. Insights into the action of phylogenetically diverse microbial expansins on the structure of cellulose microfibrils. Biotechnology for Biofuels and Bioproducts (2024).
3. Comparative assessment of chemical and biochemical approaches for the activation of lignocellulosic materials and emerging opportunities for expansin-related proteins. Cellulose (2023).
4. Molecular Cloning, In Silico Analysis, and Characterization of a Novel Cellulose Microfibril Swelling Gene Isolated from Bacillus sp. Strain AY8. Microorganisms (2023).