Elongation factor

Elongation factors are a set of proteins that function at the ribosome, during protein synthesis, to facilitate translational elongation from formation of the first to the last peptide bond of a growing polypeptide. Bacteria and eukaryotes use elongation factors that are largely homologous to each other, but with distinct structures (and different research nomenclatures).

Elongation is the most rapid step in translation. In bacteria it proceeds at a rate of 15 to 20 amino acids added per second (about 45-60 nucleotides read, per second). In eukaryotes the rate is about two amino acids per second (about 6 nucleotides read, per second). Elongation factors play a role in orchestrating the events of this process, and in ensuring the highly accuracy translation at these speeds.

Table of corresponding bacterial and eukaryotic/archael EFs

Elongation factors
BacterialEukaryotic/ArchaealFunction
EF-TueEF-1 subunit αmediates the entry of the aminoacyl tRNA into a free site of the ribosome.
EF-TseEF-1 subunit βγserves as the guanine nucleotide exchange factor for EF-Tu, catalyzing the release of GDP from EF-Tu.
EF-GeEF-2catalyzes the translocation of the tRNA and mRNA down the ribosome at the end of each round of polypeptide elongation. Shaped like EF-Tu plus tRNA.
EF-PEIF5Astimulates peptide formation by catalyzing the first synthesis step between the first amino acid (N-formylmethionine/methionine) and the second amino acid.
Note that EIF5A, the archaeal and eukaryotic homolog to EF-P, is instead considered an initiation factor.

In addition to their cytoplasmic machinery, eukaryotic mitochrondria and plastids have their own translation machineries, each with their own set of bacterial-type elongation factors. In humans, they include TUFM, TSFM, GFM1, GFM2.

As a target

Elongation factors are targets for the toxins of some pathogens. For instance, Corynebacterium diphtheriae produces its toxin, which alters protein function in the host by inactivating elongation factor (EF-2). This results in the pathology and symptoms associated with C. diphtheriae infection. Likewise, Pseudomonas aeruginosa exotoxin A inactivates EF-2.

References

    Further reading

    • Alberts, B. et al. (2002). Molecular Biology of the Cell, 4th ed. New York: Garland Science. ISBN 0-8153-3218-1.
    • Berg, J. M. et al. (2002). Biochemistry, 5th ed. New York: W.H. Freeman and Company. ISBN 0-7167-3051-0.
    • Singh, B. D. (2002). Fundamentals of Genetics, New Delhi, India: Kalyani Publishers. ISBN 81-7663-109-4.
    This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.