Fig. 3

Secretion pathway in T. reesei. Secreted cellulase will enter the classical secretion pathway, which passes through the ribosome, endoplasmic reticulum, Golgi, and secrets extracellularly. The ER lumen is amplified to give a comprehensive review of the protein assembly and ER quality control. The basic pathway for cellulase secretin is annotated as red arrow, with the assistance of multiple factors, including the PDI1, BiP1, HAC1, SNC1, etc. Insufficient folding or degradation of the secreted protein is indicated by gray arrows. Moreover, the promising secretion factors for improved cellulase production in T. reesei are also annotated aside, which need further exploration. The cellular structures are marked by purple, and the promising secretion pathways for engineering are shown with red font