Fungal loosenin-like proteins boost the cellulolytic enzyme conversion of pretreated wood fiber and cellulosic pulps.

Microbial expansin-related proteins, including loosenins, can disrupt cellulose networks and increase enzyme accessibility to cellulosic substrates. Herein, four loosenins from Phanerochaete carnosa (PcaLOOLs), and a PcaLOOL fused to a family 63 carbohydrate-binding module, were compared for ability to boost the cellulolytic deconstruction of steam pretreated softwood (SSW) and kraft pulps from softwood (ND-BSKP) and hardwood (ND-BHKP). Amending the Cellic® CTec-2 cellulase cocktail with PcaLOOLs increased reducing products from SSW by up to 40 %, corresponding to 28 % higher glucose yield. Amending Cellic® CTec-2 with PcaLOOLs also increased the release of glucose from ND-BSKP and ND-BHKP by 82 % and 28 %, respectively. Xylose release from ND-BSKP and ND-BHKP increased by 47 % and 57 %, respectively, highlighting the potential of PcaLOOLs to enhance hemicellulose recovery. Scanning electron microscopy and fiber image analysis revealed fibrillation and curlation of ND-BSKP after PcaLOOL treatment, consistent with increasing enzyme accessibility to targeted substrates.