High-Resolution Image Reveals Structure of Protein Machine

Using a high-energy X-ray beam from the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory, researchers at Yale University and the Howard Hughes Medical Institute obtained the most detailed images ever seen of the ribosome (the protein-making structure inside all living cells). NSLS is a DOE Office of Biological and Environmental Research structural biology user facility.

In prokaryotes (bacteria and other simple organisms) as well as the more complex eukaryotes, ribosomes help translate gene-encoded information into a specific protein. Ribosomes consist of two unequally sized subunits containing RNA and proteins. The smaller component binds the messenger RNA (mRNA), which contains genetic instructions that specify the amino acids required to build a particular protein. The larger ribosomal subunit attaches one amino acid to the next in the growing protein chain.

In the August 11 issue of Science, investigators reported visualizing the atomic structure of the bacterium Haloarcula marismortuis larger ribosomal subunit at an unprecedented resolution of 2.4 Å. Until this report was published, researchers did not know whether ribosomal RNA or protein was responsible for catalyzing link formation. The new images revealed the proteins deeply embedded in the RNA and their essential role in its folding. The images also showed where binding takes place, proving RNAs ability to break or form bonds. Further studies should show the orientation of mRNA and the growing proteins components in the ribosomes active catalytic site.

In this study, researchers used the 2.5-billion-electron volt beam to perform crystallography on painstakingly grown crystals of the 50S subunits. Additional data were gathered using the Advanced Photon Source at Argonne National Laboratory.

During X-ray crystallography, intense beams pass through and bounce off atoms in the crystal, where they leave a diffraction pattern that can be analyzed to determine the proteins 3-D shape. Researchers resolved the atomic structures of all 100,000 or so crystal atoms in the RNA 50S subunit. This involved carefully growing larger, more complete ribosome crystals and solving their structures at progressively higher resolutions. Each level provided information that helped scientists understand the final high-resolution map.

The electronic form of the newsletter may be cited in the following style:
Human Genome Program, U.S. Department of Energy, Human Genome News (v11n1-2).