Boosting enzymatic degradation of cellulose using a fungal expansin: Structural insight into the pretreatment mechanism

•TlEXLX1, a fungal expansin, promotes cell wall extension and cellulose degradation.•TlEXLX1 exhibits varying degrees of synergistic action with commercial cellulase.•Y291, W292, and Y327 CH–π interactions with glucose units mediate cellulose binding.•T179, D237, and D248 mediate cellulose loosening by disrupting H-bonding network.•TlEXLX1 may represent a sustainable tool for the efficient utilization of cellulose.