How equal charges in enzymes control biochemical reactions

The team investigated a well-known enzyme that has been studied extensively and is a textbook example of enzyme catalysis. Without the enzyme, the reaction is extremely slow: in fact, it would take 78 million years for half of the substrate to react. The enzyme accelerates this reaction by 10¹⁷ times, simply by positioning negative and positive charges in the active centre. Since the substrate contains a negatively charged group that is split off as carbon dioxide, it was assumed for decades that the negative charges of the enzyme serve to stress the substrate, which is also negatively charged, and accelerate the reaction. However, this hypothetical mechanism remained unproven because the structure of the reaction was too fast to be observed.

Professor Kai Tittmann's group at the Göttingen Center for Molecular Biosciences (GZMB) has now succeeded for the first time in using protein crystallography to obtain a structural snapshot of the substrate shortly before the chemical reaction. Unexpectedly, the negative charges of enzyme and substrate did not repel each other. Instead, they shared a proton, which acted like a kind of molecular glue in an attractive interaction. "The question of whether two equal charges are friends or foes in the context of enzyme catalysis has long been controversial in our field, and our study shows that the basic principles of how enzymes work are still a long way from being understood," says Tittmann. The crystallographic structures were analysed by quantum chemist Professor Ricardo Mata and his team from Göttingen University's Institute of Physical Chemistry. "The additional proton, which has a positive charge, between the two negative charges is not only used to attract the molecule involved in the reaction, but it triggers a cascade of proton transfer reactions that further accelerate the reaction," Mata explains.

"We believe that these newly described principles of enzyme catalysis will help in the development of new chemical catalysts," says Tittmann. "Since the enzyme we studied releases carbon dioxide, the most important greenhouse gas produced by human activities, our results could help develop new chemical strategies for carbon dioxide fixation."

The study involved scientists from the Göttingen Centre for Molecular Biosciences (GZMB), the Faculty of Biology and Psychology, and the Faculty of Chemistry at the University of Göttingen, as well as the Max Planck Institute for Multidisciplinary Sciences, the European Molecular Biology Laboratory (EMBL) Hamburg and the University of Toronto. The publication is dedicated to the memory of co-author Professor Ulf Diederichsen, who passed away last year.