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Two papers were published in November 2005 with structures of the Escherichia coli 70S ribosome. The structures of vacant ribosome were determined at 3.5-ångström resolution using x-ray crystallography. Then, two weeks later, a structure based on cryo-electron microsopy was published, which depicts the ribosome at 11-15 ångström resolution in the act of passing a newly synthesized protein strand into the protein-conducting channel.

First atomic structures of the ribosome complexed with tRNA and mRNA molecules were solved by using X-ray crystallography by two groups independently, at 2.8 ångström and at 3.7 ångström. These structures allow one to see the details of interactions of the Thermus thermophilus ribosome with mRNA and with tRNAs bound at classical ribosomal sites. Interactions of the ribosome with long mRNAs containing Shine-Dalgarno sequences were visualized soon after that at 4.5- to 5.5-ångström resolution.

Function

Ribosomes are the workhorses of protein biosynthesis, the process of translating mRNA into protein. The mRNA comprises a series of codons that dictate to the ribosome the sequence of the amino acids needed to make the protein. Using the mRNA as a template, the ribosome traverses each codon (3 nucleotides) of the mRNA, pairing it with the appropriate amino acid provided by a tRNA. Molecules of transfer RNA (tRNA) contain a complementary anticodon on one end and the appropriate amino acid on the other. The small ribosomal subunit, typically bound to a tRNA containing the amino acid methionine, binds to an AUG codon on the mRNA and recruits the large ribosomal subunit. The ribosome then contains three RNA binding sites, designated A, P, and E. The A site binds an aminoacyl-tRNA (a tRNA bound to an amino acid); the P site binds a peptidyl-tRNA (a tRNA bound to the peptide being synthesized); and the E site binds a free tRNA before it exits the ribosome. Protein synthesis begins at a start codon AUG near the 5' end of the mRNA. mRNA binds to the P site of the ribosome first. The ribosome is able to identify the start codon by use of the Shine-Dalgarno sequence of the mRNA in prokaryotes and Kozak box in eukaryotes.

In Figure 3, both ribosomal subunits (small and large) assemble at the start codon (towards the 5' end of the mRNA). The ribosome uses tRNA that matches the current codon (triplet) on the mRNA to append an amino acid to the polypeptide chain. This is done for each triplet on the mRNA, while the ribosome moves towards the 3' end of the mRNA. Usually in bacterial cells, several ribosomes are working parallel on a single mRNA, forming what is called a polyribosome or polysome.

Nobel Prize

The Nobel Prize in Chemistry 2009 was awarded to Drs Venkatraman Ramakrishnan, Thomas A. Steitz and Ada E. Yonath "for studies of the structure and function of the ribosome"

See also

• Aminoglycosides
• Eukaryotic translation
• Posttranslational modification
• Prokaryotic translation
• Translation (genetics)
• Wobble base pair

References

1. Schuwirth BS, Borovinskaya MA, Hau CW, Zhang W, Vila-Sanjurjo A, Holton JM, Cate JH. Structures of the bacterial ribosome at 3.5 ångström resolution. Science. 2005 Nov 4;310(5749):827-34. PMID 16272117
2. Mitra K, Schaffitzel C, Shaikh T, Tama F, Jenni S, Brooks CL 3rd, Ban N, Frank J. Structure of the E. coli protein-conducting channel bound to a translating ribosome. Nature. 2005 Nov 17;438(7066):318-24. PMID 16292303
3. Selmer, M., Dunham, C.M., Murphy, F.V IV, Weixlbaumer, A., Petry S., Kelley, A.C., Weir, J.R. and Ramakrishnan, V. (2006). Structure of the 70S ribosome complexed with mRNA and tRNA. Science , 313, 1935-1942. PMID 16959973
4. Korostelev A, Trakhanov S, Laurberg M, Noller HF. Crystal structure of a 70S ribosome-tRNA complex reveals functional interactions and rearrangements. Cell. 2006 Sep 22;126(6):1065-77
5. Yusupova G, Jenner L, Rees B, Moras D, Yusupov M. Structural basis for messenger RNA movement on the ribosome. Nature. 2006 Nov 16;444(7117):391-4
6. 2009 Nobel Prize in Chemistry, Nobel Foundation.

External links

• 70S Ribosome Architecture Animation of a working ribosome. Requires the Chime browser plugin from this site (where registration is required).
• Lab computer simulates ribosome in motion
• Role of the Ribosome, Gwen V. Childs, copied here
• Ribosome in Proteopedia - The free, collaborative 3D encyclopedia of proteins & other molecules
• Molecule of the Month © RCSB Protein Data Bank:
  • Ribosome
  • Elongation Factors

 This article incorporates public domain material from Science Primer. NCBI. Archived from the original on 2009-12-08.

• Ribozymes
• Protein biosynthesis
• Organelles