When Associate Professor Hans E.M. Christensen, Associate Professor Pernille Harris and PhD student Trine Vendelboe from DTU Chemistry with colleagues from the University of Oxford identified the first structure of the enzyme dopamine β-hydroxylase that controls conversion between two of our body’s most important neurotransmitters, dopamine and noradrenaline, they knew it was big news.
After all, a string of competent international research teams had tried to solve the riddle and hack this specific enzyme for more than 20 years to no avail. However, even the seasoned Danish researchers had not quite anticipated the enthusiastic media stir caused by the publication of the enzyme structure in Science Advances.
Within 24 hours of the press release, news media, broadcasting companies and science magazines were queuing up for a comment or an interview. That kind of media attention is quite unusual in the world of metalloproteins and the hectic days in the spotlight following breaking the news of the discovery showed very clearly, that this was no small achievement. But then, it was no chance discovery either. It took ten years of hard work and a lot of stamina to unlock the dopamine β-hydroxylase structure.
Dopamine and noradrenaline play a key role in regulating behavioral and physiological processes like memory, mood, arousal, and attention. The enzyme dopamine β-hydroxylase, that Associate Professor Hans E.M. Christensen and his team unveiled, controls the levels of dopamine and noradrenaline in our body. Malfunction in the control of the two transmitters has been linked to a number of disorders seriously affecting human life such as hypertension, depression, anxiety, Parkinson’s disease, schizophrenia, Alzheimer’s and drug dependence. Understanding the crystal structure of the enzyme, therefore, could provide an ideal target for future drug development.
“It’s never easy to map an enzyme”, Hans E.M. Christensen explains. “It’s always a laborious process and you have to be persistent, but in this case it was somewhat harder to unlock the secrets than in most cases. There were quite a few setbacks and turns along the way, but we never really doubted that it could be done, that we were on the right track. These are competent people, and we were determined to see the process through to the end as a team”.
Enzymes like these are rare in the human body, and therefore the team needed to produce sufficient material in so-called cell factories that can be controlled in vitro. After failed attempts with bacteria and yeast cells, the common fruit fly Drosophila Melanogaster provided the cells needed for the factories, and after five years of work, the first breakthrough came when the enzyme was produced, although the team still was not able to crystalize it and thereby decode the structure through X-ray crystallography. That problem was eventually solved in cooperation with researchers from University of Oxford, and in the end, Associate professor Pernille Harris from DTU and her PhD student Trine Vendelboe painstakingly build the 1200 amino acid structure by hand, one functional group at a time.
Using X-ray crystallography, the team found that the unraveled enzyme contained two new potential binding sites. One was a pocket where another molecule can bind, common to this class of enzymes. However, also a binding site for copper ions was entirely unanticipated. “This is the big surprise”, Hans E.M. Christensen says. “We have uncovered a structure of this enzyme that no-one was expecting. Now we can help the biotech industry exploit these binding sites to develop new drugs targeting the binding sites”. One such use could be the design of inhibitors modulation the dopamine β-hydroxylase involvement in PTSD and drug dependence.
Hans E.M. Christensen and his coworkers also found that dopamine β-hydroxylase seems to function by a flip-flop mechanism, where one half of the enzyme carries out the enzymatic reaction, while the other half of the enzyme unloads the noradrenaline and loads dopamine. Then, the enzyme flip-flops and the function of the two halves of the enzyme are interchanged. “The flip-flop mechanism is another unexpected phenomenon we need to explore further”, Hans E.M. Christensen states. ”It could very well shed new light on some of the numerous poorly understood disorders associated with malfunction in the noradrenaline pathway”.
Since the publication of the structure of dopamine β-hydroxylase, Hans E.M. Christensen has been busy as speaker at high-impact conferences and meetings, but back home at DTU Chemistry the work with the enzymes continue. “We have solved the original riddle and the patent is pending, but as it often is with science, the answer has bred a lot of new questions we need to tackle. This is just the beginning of an exciting journey I’m looking very much forward to embark on with my team”, Hans E.M. Christensen states.