Ribosomes structure studies

The ribosome is a unique cellular machine in that its main functional component is RNA whereas proteins seem to play only a structural role. For a long time, it has been debated whether RNA or proteins contribute most to the ribosome s function. With the determination of high-resolution crystal structures, this question could finally be answered. Clearly, these structures have revolutionized the field of ribosome studies. Already in the 1980s, Yonath and coworkers had grown crystals of active ribosomes that diffracted to about 0.6 nm (6 A) (1 A = 0.1nm) resolution. However, owing to the large size of the ribosome of about 2 500 000 Da (lDa=lgmoP), the ribosome structure was not solved to atomic resolution until tbe year 2000. 

Like most trace elements, nickel can activate various enzymes in vitro, but no enzyme has been shown to require nickel, specifically, to be activated. Howevei, mease has been shown to be a nickel metalloenzyme and has been found to contain 6 to 8 atoms of nickel per mole of enzyme (Fishbein et al.. 1976). RNA (ribonucleic add) preparations from diverse sources consistently contain nickel in concentrations many times higher than those found in native materials from which the RNA ts isolated (Wacker-Vallee, 1959 Sunderman, 1965). Nickel may serve to stabilize the ordered structure of RNA. Nickel may have a role in maintaining ribosomal structure (Tal, 1968, 1969). These studies and other information have led to the suggestion that nickel may play a role in nucleic acid and/or protein metabolism. 

The halobhilic proteins and macromolecular complexes on which structural studies are in progress include ferredoxin from H. maris-mortui (X-ray crystallography), ribosomal subunits from H. marismor-... 

Silva, A.L., Goto, L.S., Dinarte, A.R., Hansen, D., Moreira, R.A., Beltramini, L.M., Araujo, A.P. (2005). Pulchellin, a highly toxic type 2 ribosome-inactivating protein from Abrus pul-chellus. Cloning heterologous expression of A-chain and structural studies. FEBS J. 272 1201-10. 

Protein synthesis inhibition results from reversible binding of the tetracycline drugs to the 30S ribosomal subunit. This in turn prevents the attachment of aminoacyl-fRNAs to the acceptor site of the ribosomal structure (Fig. 6-17). The ribosomal mRNA complex is thus effectively precluded from initiating protein synthesis. Tetracyclines do not interfere with actual peptide bond formation, nor with the translocation process. In vitro studies with 70S ribosomes using photoaffinity techniques demonstrate binding to the 4S and 18S protein components of the 30S subunits. It is likely that these are the actual binding sites. 

Nomura, M., and Held, W. A. (1974). Reconstitution of ribosomes Studies of ribosome structure, function and assembly. In Ribosomes (M. Nomura, A. Tissieres, and P. Lengyel, Eds.), pp. 193-223. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY. 

Ostner, U., Hultin, T. The use of proteolytic enzymes in the study of ribosomal structure. Biochim. biophys. Acta (Amst.) 154, 376-387... 

Structural studies by biochemical, immunological, and physicochemical techniques are being actively pursued in many laboratories, directed towards establishment of a detailed three-dimensional map of the ribosome. 

Lake, J. A., Nonomura, Y., and Sabatini, D.D., 1974, Ribosome structure as studied by electron microscopy, m "Ribosomes", M. Nomura, A. Tissiere, P. Lengyel, eds., Cold Spring Harbor Laboratory, Long Island, N.Y., p. 543. 

Liljas, A., 1982, Structural studies of ribosome, Progr. Biophys. Mol. Biol., in press. 

Matheson, A.T., Moller, W., Amons, R., and Yaguchi, M., 1980, Comparative studies on the structure of ribosomal proteins, with emphasis on the alanine-rich acidic ribosomal, A" protein, in Ribosome Structure, Function and Genetics, G. Chambliss, G.R. Craven, J. Davies, K. Davis, L. Kahan, and M. Nomura, eds.. University Park Press, Baltimore, p. 297. 

The bacterial ribosome has been the subject of intense study for several decades. Although the general mechanisms of protein synthesis (as outlined earlier) are reasonably well understood, only recently have structures emerged which make a molecular description of ribosome function appear possible. Because of the high degree of functional and sequence conservation between bacterial and eukaryotic components of the ribosome, structural information obtained using bacterial ribosomes is expected to contribute to a universal understanding of ribosomal architecture. 

The ribosome s size challenged structural studies since its first observation in electron micrographs nearly 50 years ago. With a molecular mass of 2500 kD and dimensions about 250 A on a side, the 70S ribosome is small for electron microscopy but immense for structural studies (such as NMR and X-ray crystallography) typically applied to single molecules. 

K. Fluorometric studies on the ribosomal structure by ethidium bromide. Cell Mol Biol 1978, 23, 183-190. 

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