To date, however, no atomic-resolution image of eukaryotic ribosomes exists, and all images produced so far have been the result of Frank's electron microscope imaging and reconstruction methods.
The ribosomes of different eukaryotic organisms have only slight differences in their peripheral elements, such as specialized tools to send newly formed proteins into or through membranes. If anything, Frank expected the trypanosome's ribosome might be missing some elements, because of its sheltered life within host organisms.
"In reconstructions of ribosomes from yeast to rabbits to humans, one essentially sees the same architecture," said Frank. "It lulled us into the belief that once you've seen one ribosome, you've seen them all. It was a total surprise to see such a different structure."
Last year, Levin traveled to Frank's lab in New York with purified ribosomes from T. cruzi. There, postdoctoral fellow Haixiao Gao led the experiment, using a technique that works on a principle similar to a medical CAT scan.
First, the researchers freeze an ultrathin layer of buffer with purified ribosomes so quickly that the water has no chance to crystallize and damage the ribosomes. Then, the frozen sample is imaged with an electron beam in the transmission electron microscope.
A CAT scan takes readings of a single body from different angles to reconstruct its three-dimensional images, but the microscope catches hundreds of ribosomes at different angles in a single snapshot. Frank and his colleagues have developed a battery of complex mathematical techniques to reconcile the images at different angles. From a total of up to 30,000 ribosome images, they assemble a final three-dimensional image of a single ribosome.
A ribosome binds to mRNA w
Source:Howard Hughes Medical Institute