Insights into the action of phylogenetically diverse microbial expansins on the structure of cellulose microfibrils

Majid Haddad Momeni*, Aleksi Zitting, Vilma Jäämuru, Rosaliina Turunen, Paavo Penttilä, Garry W. Buchko, Salla Hiltunen, Natalia Maiorova, Anu Koivula, Janak Sapkota, Kaisa Marjamaa, Emma R. Master*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Background: Microbial expansins (EXLXs) are non-lytic proteins homologous to plant expansins involved in plant cell wall formation. Due to their non-lytic cell wall loosening properties and potential to disaggregate cellulosic structures, there is considerable interest in exploring the ability of microbial expansins (EXLX) to assist the processing of cellulosic biomass for broader biotechnological applications. Herein, EXLXs with different modular structure and from diverse phylogenetic origin were compared in terms of ability to bind cellulosic, xylosic, and chitinous substrates, to structurally modify cellulosic fibrils, and to boost enzymatic deconstruction of hardwood pulp. 

Results: Five heterogeneously produced EXLXs (Clavibacter michiganensis; CmiEXLX2, Dickeya aquatica; DaqEXLX1, Xanthomonas sacchari; XsaEXLX1, Nothophytophthora sp.; NspEXLX1 and Phytophthora cactorum; PcaEXLX1) were shown to bind xylan and hardwood pulp at pH 5.5 and CmiEXLX2 (harboring a family-2 carbohydrate-binding module) also bound well to crystalline cellulose. Small-angle X-ray scattering revealed a 20–25% increase in interfibrillar distance between neighboring cellulose microfibrils following treatment with CmiEXLX2, DaqEXLX1, or NspEXLX1. Correspondingly, combining xylanase with CmiEXLX2 and DaqEXLX1 increased product yield from hardwood pulp by ~ 25%, while supplementing the TrAA9A LPMO from Trichoderma reesei with CmiEXLX2, DaqEXLX1, and NspEXLX1 increased total product yield by over 35%. 

Conclusion: This direct comparison of diverse EXLXs revealed consistent impacts on interfibrillar spacing of cellulose microfibers and performance of carbohydrate-active enzymes predicted to act on fiber surfaces. These findings uncover new possibilities to employ EXLXs in the creation of value-added materials from cellulosic biomass.

Original languageEnglish
Article number56
Number of pages16
JournalBiotechnology for Biofuels and Bioproducts
Issue number1
Publication statusPublished - 23 Apr 2024
MoE publication typeA1 Journal article-refereed


  • Carbohydrate-active enzymes
  • Cellulose
  • Defibrillation
  • Expansin
  • Non-lytic


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