Researchers at the Ruhr University Bochum, Germany and the Swedish University in Uppsala have discovered a new mechanism with which switch proteins can be switched off. Switch proteins such as the Ras protein regulate many processes in the body and are involved in the development of diseases such as cancer.
The GTP molecule, which is bound to the proteins, is decisive for switching off many switch proteins. If one of the three phosphate groups is split from GTP via a chemical reaction, the protein switches to "off", which has an effect on cellular processes. "The proteins are extremely efficient and are able to carry out reactions that normally take billions of years within fractions of a second," said Klaus Gerwert.
At least one water molecule is always involved in the switch-off process. Previously, researchers assumed that this water molecule had to be activated by a reaction partner transferring a proton to the water molecule. "For decades there has been controversy as to whether this reaction partner is the GTP itself or part of the protein," says Carsten Kötting, one of the authors from the Bochum team. "In the current study, we surprisingly discovered a completely new mechanism in which activation works without the transfer of a proton.
Using computer-aided calculation methods, the team investigated all switch-off options for seven different protein systems. The scientists were given different speeds for the switch-off process. They compared the calculated velocities with values measured experimentally by time-resolved infrared spectroscopy.
While the values for the two previously suspected mechanisms differed greatly, theory and experiment showed the same results for the newly found mechanism - for all seven systems tested. "The agreement shows that our newly discovered switch-off mechanism is universally valid and thus relevant for many cellular processes," summarizes Till Rudack.
"Diseases often involve a defect in the switch-off mechanism of key proteins," says Till Rudack. "In order to understand the molecular processes underlying diseases and in order to develop therapies, we need to understand the switch-off mechanism”.
For example, the newly discovered switch-off mechanism is responsible for the switching of Ras. For decades, researchers have been trying to find a drug that attacks the dysfunctional Ras protein in human tumors. "We assume that our results will explain the unsuccessful search," said Klaus Gerwert. "New starting points for cancer drugs can now be found on the basis of the now correct molecular switch-off mechanism".
Ana R. Calixto, Cátia Moreira, Anna Pabis, Carsten Kötting, Klaus Gerwert, Till Rudack, Shina C.L. Kamerlin: GTP hydrolysis without an active site base: a unifying mechanism for Ras and related GTPases, in: Journal of the American Chemical Society, 2019, DOI: 10.1021/jacs.9b03193