How does a cell keep track of its many signals? One answer lies in tiny sugar tags that are constantly added to and removed from proteins. This process, known as O-GlcNAcylation, acts like on/off switches for proteins that regulate everything from cell growth to stress responses.
Until now, scientists viewed the mechanism as binary: the enzyme removing the tag was either on or off. But a new study, published in Nature Communications, shows the picture is far more nuanced.

“It’s a bit like discovering that the switch doesn’t just turn on and off, but can also work like a dimmer. Our results show that OGA not only removes the sugar tags, but that a specific part of the enzyme can actually regulate how much the activity is turned up or down,” says Sara Basse Hansen, postdoc and co-first author of the study.

A flexible regulator

The enzyme OGA is responsible for removing the sugar tags on thousands of different proteins. The researchers have now shown that its so-called pHAT domains play an active role in fine-tuning how OGA works.
Using cryo-electron microscopy and biochemical analyses, the team was able to follow how the pHAT domains move relative to the catalytic core. These movements change the environment around the active site and thereby how efficiently OGA functions. The findings raise the possibility that this regulation could turn out to influence which proteins OGA acts on, but further evidence is needed to confirm this.

“It was a huge surprise for us, because we thought the pHAT domains were just static and symmetrical. Instead, we see that they loosen and move much more freely – and that changes the entire picture of how the enzyme works,” says Sergio Galán Bartual, co-first author of the study and postdoc in Daan van Aalten’s group at the Department of Molecular Biology and Genetics (MBG), Aarhus University.

Perspectives for disease treatment

O-GlcNAcylation affects thousands of proteins in the body and is implicated in a wide range of diseases, including cancer, diabetes and neurodegenerative disorders such as Alzheimer’s.
Until now, attempts have focused on developing drugs that completely block OGA’s active sites, which shuts down all its activity everywhere. But this has caused severe side effects, as the enzyme influences so many different processes.

“If instead you can gradually adjust the activity – as with a light dimmer – it opens the door to a completely new approach. Depending on how this regulation works, it could mean simply reducing the enzyme’s overall activity more gently or even influence which proteins it acts on. That would raise the possibility of targeting specific disease processes – for example, those involving proteins like tau in Alzheimer’s - while leaving much of its normal function untouched. We are still very far from clinical application, but our results provide an important first step,” says Sara.

Years of work coming together

The study is the result of a long-standing project in van Aalten’s group, which was initiated in Dundee. The first authorship is shared between Sara Basse Hansen and Sergio Galán Bartual, both from van Aalten’s group at MBG in Aarhus.
The work has stretched over several years, and only after a series of methodological breakthroughs were the researchers able to piece everything together.

“For me personally it was quite an incredible experience when everything suddenly fell into place over Christmas and New Year. Once we had all the data in front of us, the connections became clear – and that was the breakthrough we had been waiting for,” says Sara.

“It is also a project where many people have contributed along the way, from biochemical assays to advanced microscopy. That makes it all the more satisfying that we can now share the results,” adds Sergio.

A window to the future

Although the study is basic research, it opens new perspectives. By understanding OGA’s regulation at the atomic level, scientists gain a stronger foundation for designing more precise interventions in cellular biochemistry.

“This is only the first step, but it shows that the cell’s control systems are much more flexible than we thought. In the long run, this could enable us to develop medicines that are both more targeted and with fewer side effects,” concludes Sara.

Read the publication in Nature Communications