Researchers team have determined for the first time the high-resolution structure of a complex (R2TP) involved in key processes for cell survival and diseases such as cancer. This achievement has been made possible by using high-resolution cryo-electron microscopy, a technique brought to the CNIO thanks to Óscar Llorca, director of the Structural Biology Programme. The study was published in Nature Communications.

This technique can capture images of individual molecules, which are used to determine their structure and to ascertain biological processes in atomic detail. Researchers have used this technique to learn about the structure and functioning of a complex system called R2TP, which is involved in various key processes for cell survival such as the activation of the kinases mTOR, ATR and ATM, proteins that are the target of various cancer drugs currently being developed.

Complex and versatile 'assembly machinery.'

mTOR, ATR, and other related kinases do not work in isolation but rather by interacting and forming complexes with other proteins, which are essential for their normal functioning. The assembly of these structures with multiple components does not take place in cells spontaneously. The R2TP system and the HSP90 chaperone are crucial for the assembly and activation of mTOR and other related kinases, but how this happens in cells is still somewhat of a mystery. 

By cryo-electron microscopy, they have been able to visualize, for the first time, the high-resolution structure of the human R2TP system," states Llorca. The microscope images show that R2TP is a large platform capable of putting HSP90 in contact with the kinases on which HSP90 must act. When viewed under the microscope, R2TP looks like a jellyfish with three very flexible 'tentacles' made up of RPAP3 protein.

The kinases of the mTOR family are recruited to the base of this jellyfish's 'head,' while the tentacles hooked HSP90 and taken to the kinases, thanks to their flexibility. This first observation of the human R2TP system has allowed us to understand its structure and functioning mechanisms, which were previously unknown. Our next steps will be to study the details of how R2TP and HSP90 can assemble the complexes made up of kinases of the mTOR family, to find ways of interfering with these processes.

The R2TP system is also involved in the activation of other essential molecules for the cell and in the development of cancer, such as the RNA polymerase, telomerase, or the 'splicing' system, areas that we intend to explore in the future.