The Corn Smut Fungus Ustilago maydis as an Alternative Expression System for Biopharmaceuticals

Protein pharmaceuticals constitute a heavily increasing market. Thus, there is an urgent need to efficiently produce the molecules of interest. In a quest to develop a novel protein production system, the corn smut fungus Ustilago maydis was recently established as an expression platform. Inspired by the discovery of an unconventional secretion pathway used by the fungus to secrete the endochitinase Cts1, this eukaryotic system was employed to export heterologous proteins using Cts1 as a carrier. U. maydis displays several features that indicate a great potential for its utilization in biotechnology. However, as seen in other fungi, some bottlenecks were also identified such as limiting transcriptional levels and proteolytic degradation. This initially led to low amounts of secreted proteins. Therefore, the expression system was optimized by improving expression levels and reducing proteolytic degradation using a single-chain antibody as a proof-of-principle. Hence, optimized U. maydis strains are now on a promising way to be exploited for different biotechnological applications.