Sarah Prexler successfully defended her PhD thesis

Today, Sarah Prexler successfully defended her PhD thesis on structure-function relationships of plant polyphenoloxidases, in the presence of her Doctoral Committee consisting of Bruno Moerschbacher, Prof. Bodo Philipp from the Institute of Molecular Microbiology and Biotechnology of our university, and Prof. Uwe Bornscheuer from the Institute of Biochemistry at University of Greifswald. Her PhD was financially supported by a doctoral fellowship from the Deutsche Bundesstiftung Umwelt DBU. Sarah has continued the good tradition of a small PPO subgroup within our group, braking ground in enzyme engineering, as a pioneer for later work on chitin and chitosan related enzymes. Her focus was on substrate specificity of dandelion group 1 and 2 PPOs, first defining a “substrate selector” amino acid guarding the entrance to the active site of the enzyme, allowing or denying entrance to positively or negatively charged substrates, depending on the residue occupying this position. This was followed by a thorough experimental study of different theoretical explanations for the difference between PPOs with mono- and/or diphenolase activity where she clearly showed that even very highly published papers are sometimes not worth the paper on which they are printed (or the electrons spent on sending them around the world). In collaboration with Prof. Hensel’s group at the Institute of Pharmaceutical Biology and Phytochemistry, she then isolated and characterised the first natural PPO substrates from dandelion plants. And together with her last Master student, Martin Frassek, she finally started our first mutational library which has since been followed by a few others - with highly promising results. Unfortunately, though, Sarah’s work may have been the last PPO project in our group - there is no successor in sight. That’s because Sarah is unique! She has even be in the pond already before the official hooding ceremony.