Veröffentlicht 27. Juni 2011

Climbing the Everest with polar bears

In her lecture today, Ada Yonath compared her scientific quest to determine the structure of the ribosome to a climb of the Mount Everest. Time after time she thought that she had reached the peak, only to discover a taller summit. While her journey was long and arduous, Yonath eventually reached the top and was rewarded with a spectacular view of the ribosomal landscape. She shared some of those insights with her audience today. 

To solve the structure of any molecule, scientists first need to make crystals from it. The same is true for the ribosome, one of the cell’s most important molecules (it converts RNA into proteins). But crystallizing the ribosome turned out to be impossible using conventional methods. As unlikely as it sounds, Ada Yonath first found some evidence that ribosomes can crystallize in a paper about polar bears.

In that paper it was described how the ribosomes of polar bears become stacked when they go into hibernation. In this way, the ribosomes maintain their integretiy, Yonath explained. She saw a potential application in this finding: if under the right conditions ribosomes form some faint but detactable order by packing together, surely there must be a way to crystallize them as well?

This insight turned out to be a first glimpse of the mountain. It took many years of work before Yonath and her colleagues found out how she should convince the ribosome to form crystals. She was aon the right track by trying to crystallize the robust ribosomes from bacteria that live in extreme conditions, but even these sturdy molecules were destroyed by the X-rays that are used in the structural determination of proteins.

Yonath soon found the solution to this problem In 1984, she discovered that flash-freezing the ribosome crystals protected them from the damaging X-rays. With the ribosomes fixed at sub-zero temperatures, the analogy to hibernating polar bears is complete. Cryocrystallography, as the freezing treatment became known, was established as a routine procedure soon afterwards.

Now that the ribosomes had been crystallized, its structure could be solved. Still it would take almost two decades before the ‚final‘ structures of the ribosome was published. Final, because these were the first descriptions of the ribosome at such a high resolution that the position of every single atom was known. ‚Final‘, because there is not a single ribosome. The ribosome binds to molecules such as tRNAs, and all these binding events lead to different structures and crystals.

With the ribosome structure solved, there suddenly was a lot more to see. The molecular choreography of tRNAs, proteins and ribosomes could now be studied, for example. Yonath also showe examples how it became possible to study how bacteria resistant to the antibiotics that target the ribosome. She also mentioned tha the ancient RNA core of the ribosome hints at a world that was dominated by RNA instead of proteins. And perhaps the ribosome also holds the secret to the origin of proteins and the genetic code… One thing is certain: plenty of peaks await.