To understand how the biocatalyst works, lead author Konstantin Richter first used crystals to elucidate the spatial structure of the enzyme in his doctoral thesis. "In a way, we were following up on the determination of the first structure of a PET-degrading enzyme," says Professor Norbert Sträter, who heads the crystallographic investigations. "That was almost ten years ago, when Wolfgang Zimmermann established this biotechnological enzyme research in Leipzig. At that time, hardly anyone had it on their radar."
To extract the secrets of PHL7's highly efficient reaction acceleration from the static crystal structures, Christian Sonnendecker enlisted the help of other experts in his research. The working groups led by Georg Künze and Christian Wiebeler used computer simulations of protein dynamics as well as quantum chemical calculations to understand the reaction mechanism and, in particular, the contribution of individual amino acids to the binding of the PET polymer, and to design better enzymes. "These predictions and calculations are extremely helpful in rationally improving an enzyme," explains Sonnendecker, "but in the end, of course, the experiment decides."
There was considerable agreement between the experimental data and the theoretical calculations. "We realised the proposed changes to the enzyme by genetic engineering and were able to further increase both its activity and its stability, which is enormously important for technical applications." Too strong binding of the enzyme to the polymeric plastic substrate would be counterproductive, the biochemist explains with regard to the proposed sliding mechanism, according to which a binding channel leads the substrate to the active centre. "Sometimes less is more," says Sonnendecker.