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Elongation factor

Proteins functioning in translation

Elongation factors are a set of proteins that function at the ribosome, during protein synthesis, to facilitate translational elongation from the formation of the first to the last peptide bond of a growing polypeptide. Most common elongation factors in prokaryotes are EF-Tu, EF-Ts, EF-G. 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 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 high accuracy translation at these speeds.

Nomenclature of homologous EFs

Bacterial	Eukaryotic/Archaeal	Function
EF-Tu	eEF-1A (α)	mediates the entry of the aminoacyl tRNA into a free site of the ribosome.
EF-Ts	eEF-1B (βγ)	serves as the guanine nucleotide exchange factor for EF-Tu, catalyzing the release of GDP from EF-Tu.
EF-G	eEF-2	catalyzes the translocation of the tRNA and mRNA down the ribosome at the end of each round of polypeptide elongation. Causes large conformation changes.
EF-P	eIF-5A	last1=Rossi	first1=D	last2=Kuroshu	first2=R	last3=Zanelli	first3=CF	last4=Valentini	first4=SR	title=eIF5A and EF-P: two unique translation factors are now traveling the same road.	journal=Wiley Interdisciplinary Reviews. RNA	date=2013	volume=5	issue=2	pages=209–22	doi=10.1002/wrna.1211	pmid=24402910	s2cid=25447826 }}
EF-4	(None)	Proofreading
Note that EIF5A, the archaeal and eukaryotic homolog to EF-P, was named as an initiation factor but now considered an elongation factor as well.

In addition to their cytoplasmic machinery, eukaryotic mitochondria and plastids have their own translation machinery, each with their own set of bacterial-type elongation factors. In humans, they include TUFM, TSFM, GFM1, GFM2, GUF1; the nominal release factor MTRFR may also play a role in elongation.

In bacteria, selenocysteinyl-tRNA requires a special elongation factor SelB () related to EF-Tu. A few homologs are also found in archaea, but the functions are unknown.

As a target

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

References

(2001). "Elongation Factors; Translation".
(July 2012). "The Many Roles of the Eukaryotic Elongation Factor 1 Complex". Wiley Interdisciplinary Reviews. RNA.
(July 2017). "Dynamic basis of fidelity and speed in translation: Coordinated multistep mechanisms of elongation and termination". Protein Science.
(March 1992). "Elongation factor Tu: a molecular switch in protein biosynthesis". Molecular Microbiology.
(May 2003). "Two crystal structures demonstrate large conformational changes in the eukaryotic ribosomal translocase.". Nature Structural Biology.
(2013). "eIF5A and EF-P: two unique translation factors are now traveling the same road.". Wiley Interdisciplinary Reviews. RNA.
(7 August 2007). "Structure of the Chloroplast Ribosome: Novel Domains for Translation Regulation". PLOS Biology.
(2011). "Evolution of elongation factor G and the origins of mitochondrial and chloroplast forms". Molecular Biology and Evolution.
"KEGG DISEASE: Combined oxidative phosphorylation deficiency".
(21 January 2011). "An ancient family of SelB elongation factor-like proteins with a broad but disjunct distribution across archaea". BMC Evolutionary Biology.
(1984). "Cellular ADP-ribosyltransferase with the same mechanism of action as diphtheria toxin and Pseudomonas toxin A". Proc. Natl. Acad. Sci. U.S.A..

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