Scientists have used biochemistry and low-resolution electron microscopy to map much of the ribosome's structural changes throughout its protein-making cycle. But key steps remained unclear, such as a ratchet-like motion of the small ribosomal subunit relative to the large subunit as it moves in one direction along the messenger RNA to make a protein. These parts rotate relative to another, but scientists didn't know how this large-scale twisting motion worked in molecular detail or why it didn't simply wrench the entire ribosome apart.
To find out, the scientists turned to the Advanced Light Source, a synchrotron located at Berkeley Lab that generates intense x-rays to probe the fundamental properties of molecules. Using beamline 8.3.1 and the SIBYLS beamlines, they determined the structure of Escherichia coli ribosomes in two key states for the first time at an atomic-scale resolution. In the first state, transfer RNA is bound to the two subunits in a configuration that occurs after the ribosome has made and released a protein. In the second state, the ribosome's subunits are fully rotated, which occurs when the subunits are recycled and ready to make another protein. The scientists used x-ray crystallography to piece together these structures at a resolution of approximately 3.2 ngstroms (one ngstrom is a ten-billionth of a meter, about the radius of the smallest atoms).
The resulting structures, which are two to three times higher resolution than previous images of the ribosome at these states, capture th
|Contact: Dan Krotz|
DOE/Lawrence Berkeley National Laboratory