Stepwise genetic modification for efficient expression of heterologous proteins in Aspergillus nidulans.

Filamentous fungi are widely used in food fermentation and therapeutic protein production due to their prominent protein secretion and post-translational modification system. Aspergillus nidulans is an important model strain of filamentous fungi, but not a fully developed cell factory for heterologous protein expression. One of the limitations is its relatively low capacity of protein secretion. To alleviate this limitation, in this study, the protein secretory pathway and mycelium morphology were stepwise modified. With eGFP as a reporter protein, protein secretion was significantly enhanced through reducing the degradation of heterologous proteins by endoplasmic reticulum-associated protein degradation (ERAD) and vacuoles in the secretory pathway. Elimination of mycelial aggregation resulted in a 1.5-fold and 1.3-fold increase in secretory expression of eGFP in typical constitutive and inducible expression systems, respectively. Combined with these modifications, high secretory expression of human interleukin-6 (HuIL-6) was achieved. Consequently, a higher yield of secretory HuIL-6 was realized by further disruption of extracellular proteases. Overall, a superior chassis cell of A. nidulans suitable for efficient secretory expression of heterologous proteins was successfully obtained, providing a promising platform for biosynthesis using filamentous fungi as hosts. KEY POINTS: • Elimination of mycelial aggregation and decreasing the degradation of heterologous protein are effective strategies for improving the heterologous protein expression. • The work provides a high-performance chassis host △agsB-derA for heterologous protein secretory expression. • Human interleukin-6 (HuIL-6) was expressed efficiently in the high-performance chassis host △agsB-derA.