Structural differences of hydroxycinnamoyl transferases in Lamiaceae - Part 1: The structure of rosmarinic acid synthase

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Hydroxycinnamoyltransferases (HCTs) are important enzymes in plant metabolism, in this project we are interested in the HCTs from the BAHD acyltransferase superfamily, especially within one phylogenetic clade. These HCTs transfer a hydroxycinnamoyi moiety from coenzyme A to an acceptor substrate such as shikimate, quinate or hydroxyphenyllactate which finally results in the formation of compounds like monolignols, chlorogenic acid and rosmarinic acid, respectively. The HCTs involved in these biosyntheses show high homology. Despite their importance for plant metabolism, structural information on these enzymes is scarce, but it is urgently needed to explain the diverse substrate acceptance that was reported for HCTs as well as the formation of esters and amides by the same enzyme. From an evolutionary point of view, the changes in the active centres of HCTs resulting in different substrate preferences are interesting. During the first application period we have tried to crystallise rosmarinic acid synthase (RAS) from Coleus blumei - unfortunately without sufficient success. We now want to apply our ample experiences with handling HCTs for a novel attempt to get insight into the structure of HCTs. Modelling and substrate docking will be used besides crystallisation. Further parts of this project are site-directed mutagenesis and construction of chimeric proteins of different HCTs with subsequent testing of their substrate acceptance.