S83: Prenylating enzymes—Structure, function, and new aspects of the catalytic mechanisms

Prenyl transferring enzymes are at the basis of the vast isoprenoid natural product diversity. All activate an (oligo) prenyl diphosphate to form stabilized prenyl cations as reactive intermediate. So far, aromatic amino acids have been suggested to stabilize the cations. Their role is elucidated further, but most importantly, nucleophilic amino acids, specifically methionine, are suggested as additional or alternative aids for cation stabilization. This suggestion is supported by site directed mutagenesis, bioinformatics, ab initio calculations, and modeling studies. All investigations base on a model of the membrane bound p-hydroxybenzoic acid oligoprenyl transferase (UbiA-enzyme) and on X-ray structures of NphB prenyl transferase from Streptomyces coelicolor. For the latter, the substrate specificity can be explained consistently for the first time. In addition, a new catalytic diad composed of Tyr(His) and Asp is identified as important player for proton-relay in intermediates and finalizing deprotonation of many prenyl transferring and cyclizing enzymes.