The major cellulases CBH-1 and CBH-2 of Neurospora crassa rely on distinct ER cargo adaptors for efficient ER-exit.

Abstract

Filamentous fungi are native secretors of lignocellulolytic enzymes and are used as protein-producing factories in the industrial biotechnology sector. Despite the importance of these organisms in industry, relatively little is known about the filamentous fungal secretory pathway or how it might be manipulated for improved protein production. Here, we use Neurospora crassa as a model filamentous fungus to interrogate the requirements for trafficking of cellulase enzymes from the endoplasmic reticulum to the Golgi. We characterized the localization and interaction properties of the p24 and ERV-29 cargo adaptors, as well as their role in cellulase enzyme trafficking. We find that the two most abundantly secreted cellulases, CBH-1 and CBH-2, depend on distinct ER cargo adaptors for efficient exit from the ER. CBH-1 depends on the p24 proteins, whereas CBH-2 depends on the N. crassa homolog of yeast Erv29p. This study provides a first step in characterizing distinct trafficking pathways of lignocellulolytic enzymes in filamentous fungi.