Landmark Progress In Understanding Ribosome Structure-- Research Done At Brookhaven Lab's Light Source

The ribosome is the largest and most complex component of a cell to be successfully studied via x-ray crystallography. Researchers from the University of Utah; the Medical Research Council Laboratory of Molecular Biology, Cambridge, England; and Brookhaven Lab presented a model of the small ribosomal subunit known as 30S, from the bacterium Thermus thermophilus. Yale University and Brookhaven researchers reported on the structure of the large ribosomal subunit known as 50S, from the bacterium Haloarcula marismortui. These two independent research efforts point the way for future study of large ribosome complexes.

Malcolm Capel, a Brookhaven National Laboratory biophysicist who is a co-author on both Nature papers, explained, "This research is a technical and scientific tour de force. On a basic science level, these findings represent a giant step on the road to understanding how living organisms make proteins. On a more practical level, many bacterial infections are stopped by antibiotics, which work by inhibiting the production of ribosomes in bacterial cells. Better structural knowledge of ribosomes may lead to developing more effective antibiotics through computer-modeling. Also, ribosomes are used by industry to make important enzymes, which promote chemical reactions. This new structural information may be helpful for developing further industrial applications."

To gain this new data, the researchers grew crystals of ribosomes, and, to protect them from radiation damage, froze them to 173°C. Crystals provided the researchers with molecules that are arranged in a regularly repeated pattern for their studies. An intense x-ray beam from the Light Source penetrated the crystal, resulting in tens of thousands of diffraction spots on a computerized imaging detector. The researchers measured the position and intensity of each spot, and then mathematically calculated the electron density of the sample. From these data, they were able to build a molecular model of the ribosomal structure.

Specifically, the ribosome translates the genetic code of nucleic acids known as messenger RNAs into chains of amino acids that make up proteins. The 30S ribosomal subunit recognizes messenger RNA and insures that the sequence of information in the RNA is correctly copied into a protein. The 50S subunit performs the chemical steps involved in linking together amino acids to form proteins. The 30S and 50S subunits work together to generate proteins in all living cells.

Both Nature papers report on structural components at a resolution of five angstroms, a measurement that is about one ten-thousandth the thickness of a human hair. While ribosomes make proteins, they are also composed of proteins and RNA themselves, and, with this resolution, the researchers were able to differentiate a protein from the ribosomal complex. In addition, the surface topology of both subunits is revealed in detail, showing the way the two subunits fit together to form a whole, functional 70S ribosome complex.

The authors of paper describing the ribosome 30S subunit are William M. Clemons, Jr., Joanna L.C. May, Brian T. Wimberly, and John P. McCutcheon from the University of Utah and Venki Ramakrishnan from the University of Utah and the Medical Research Council, Cambridge, England; and Malcolm Capel, from Brookhaven National Laboratory. The research on the large ribosomal 50S subunit is reported by Nenad Ban, Poul Nissen, Peter B. Moore and Thomas A. Steitz from Yale University; and Malcolm Capel from Brookhaven.

The U.S. Department of Energy's Brookhaven National Laboratory creates and operates major facilities available to university, industrial and government personnel for basic and applied research in the physical, biomedical and environmental sciences, and in selected energy technologies. The Laboratory is operated by Brookhaven Science Associates, a not-for-profit research management company, under contract with the U.S. Department of Energy.