Towards a detailed understanding of MEL biosynthesis to improve tailor-made biosurfactant production in the corn smut Ustilago maydis

• Applicant: Dr. Björn Sandrock
• Subject Area: Microbial Ecology and Applied Microbiology ; Metabolism, Biochemistry and Genetics of Microorganisms
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 521037434

Fungal glycolipids are a versatile group of secondary metabolites, that act as biosurfactants with promising features for biotechnology. Mannosylerythritol lipids (MELs) are glycolipids produced by various basidiomycetous yeasts including Ustilago maydis, a well-established model organism in fungal genetics. MELs consist of a central carbohydrate moiety linked to acyl and acetyl groups. I have contributed to the elucidation of MEL biosynthesis before; e.g. demonstration of partial compartmentalization of MEL biosynthesis inside of peroxisomes and characterization of enzymes involved in MEL production. Very recently, we could show that acyltransferases (Mac1, Mac2 and Mac3) from different organisms can be combined to program MEL biosynthesis. We now aim to better understand, how Mac1, Mac2 and Mac3, which modify the sugar backbone with acyl groups of very different lengths measure the length of the fatty acid substrate. We will combine genetics (creation of chimeric enzymes and subsequent analysis of in vivo products) and structural biology (crystallization and elucidation of the structure of Mac variants with different substrate specificity). We could already identify chimeric enzymes with altered substrate specificity. With the proposed combination of experiments, we hope to contribute to a more mechanistic picture of MEL biosynthesis and to a better understanding of substrate recognition/utilization by acyltransferases. In a second part we plan to produce novel MEL molecules based on a recently developed strategy. We have shown that acyltransferases involved in MEL production from different fungi can be freely combined without losing substrate specificity. We now are going to use this finding systematically to create a versatile collection of MELs with a great potential as novel biosurfactants. Both aims are interconnected and knowledge gained in part 2 might contribute to a better understanding of the specificity determinants of acyltransferases addressed in part 1. The mechanistic characterization of MEL biosynthesis has only started with our more recent publications. A detailed understanding will be an important prerequisite for the synthesis of desired MELs as potential biosurfactants and for further applications. Especially, the characterization of substrate specificity of acyltransferases might be interesting for a broader audience as many different enzymes transfer acyl groups but there is only limited knowledge how the size of fatty acids substrates can be measured.

• DFG Programme: Research Grants