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

Abstract

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Five heterogeneously produced EXLXs (<jats:italic>Clavibacter michiganensis; Cmi</jats:italic>EXLX2, <jats:italic>Dickeya aquatica; Daq</jats:italic>EXLX1, <jats:italic>Xanthomonas sacchari; Xsa</jats:italic>EXLX1, <jats:italic>Nothophytophthora sp.; Nsp</jats:italic>EXLX1 and <jats:italic>Phytophthora cactorum; Pca</jats:italic>EXLX1) were shown to bind xylan and hardwood pulp at pH 5.5 and <jats:italic>Cmi</jats:italic>EXLX2 (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 <jats:italic>Cmi</jats:italic>EXLX2, <jats:italic>Daq</jats:italic>EXLX1, or <jats:italic>Nsp</jats:italic>EXLX1. Correspondingly, combining xylanase with <jats:italic>Cmi</jats:italic>EXLX2 and <jats:italic>Daq</jats:italic>EXLX1 increased product yield from hardwood pulp by ~ 25%, while supplementing the <jats:italic>Tr</jats:italic>AA9A LPMO from <jats:italic>Trichoderma reesei</jats:italic> with <jats:italic>Cmi</jats:italic>EXLX2, <jats:italic>Daq</jats:italic>EXLX1, and <jats:italic>Nsp</jats:italic>EXLX1 increased total product yield by over 35%.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>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.</jats:p></jats:sec>

Topics

• impedance spectroscopy
• surface
• cellulose
• size-exclusion chromatography
• X-ray scattering