View source for EF-G

{{Short description|Prokaryotic elongation factor}}
{{Infobox enzyme 
| AltNames = Elongation factor G, EF-G
| name = Protein-synthesizing GTPase
| image = EF-G Post State PDB 4V5F.jpg
| image_size = 200px
| caption = 
| EC_number = 3.6.5.3
| CAS_number = 
| GO_code = 
}}
{{Pfam box
|Name=Translation elongation factor EFG/EF2
|Symbol=Transl_elong_EFG/EF2
|InterPro=IPR004540
|SCOP=1n0u
}}
{{Pfam box
|Name=EFG/EF2, domain IV
|Symbol=EFG_IV
|Pfam=PF03764
|Pfam_clan=CL0329
|CDD=cd01434
|SMART=SM00889
}}

'''EF-G''' ('''elongation factor G''', historically known as '''translocase''') is a [[prokaryotic elongation factor]] involved in [[Translation (biology)|mRNA translation]]. As a [[GTPase]], EF-G catalyzes the movement (translocation) of [[transfer RNA]] (tRNA) and [[messenger RNA]] (mRNA) through the [[ribosome]].<ref name=shoji>{{cite journal|last1=Shoji|first1=S|last2=Walker|first2=SE|last3=Fredrick|first3=K|title=Ribosomal translocation: one step closer to the molecular mechanism|journal=ACS Chem Biol|date=2009|doi=10.1021/cb8002946|pmid=19173642|volume=4|issue=2|pages=93–107|pmc=3010847}}</ref>

== Structure ==
Encoded by the ''fusA'' gene on the ''str'' operon,<ref name="Post 4660–4666">{{Cite journal|last1=Post|first1=L. E.|last2=Nomura|first2=M.|date=1980-05-25|title=DNA sequences from the str operon of Escherichia coli|journal=The Journal of Biological Chemistry|volume=255|issue=10|pages=4660–4666|doi=10.1016/S0021-9258(19)85545-X|issn=0021-9258|pmid=6989816|doi-access=free}}</ref> EF-G is made up of 704 amino acids that form 5 [[Protein domain|domains]], labeled Domain I through Domain V. Domain I may be referred to as the G-domain or as Domain I(G), since it binds to and hydrolyzes [[guanosine triphosphate]] (GTP). Domain I also helps EF-G bind to the ribosome, and contains the N-terminal of the [[Peptide|polypeptide]] chain.<ref>{{Cite journal|last1=Liu|first1=Kaixian|last2=Rehfus|first2=Joseph E.|last3=Mattson|first3=Elliot|last4=Kaiser|first4=Christian M.|date=2017-07-01|title=The ribosome destabilizes native and non-native structures in a nascent multidomain protein|journal=Protein Science|language=en|volume=26|issue=7|pages=1439–1451|doi=10.1002/pro.3189|pmid=28474852|pmc=5477528|issn=1469-896X}}</ref><ref name=":1">{{Cite journal|last1=Carlson|first1=Markus A.|last2=Haddad|first2=Bassam G.|last3=Weis|first3=Amanda J.|last4=Blackwood|first4=Colby S.|last5=Shelton|first5=Catherine D.|last6=Wuerth|first6=Michelle E.|last7=Walter|first7=Justin D.|last8=Spiegel|first8=Paul Clint|date=2017-06-01|title=Ribosomal protein L7/L12 is required for GTPase translation factors EF-G, RF3, and IF2 to bind in their GTP state to 70S ribosomes|journal=The FEBS Journal|language=en|volume=284|issue=11|pages=1631–1643|doi=10.1111/febs.14067|pmid=28342293|pmc=5568246|issn=1742-4658}}</ref> Domain IV is important for translocation, as it undergoes a significant conformational change and enters the A site on the [[Prokaryotic small ribosomal subunit|30S ribosomal subunit]], pushing the mRNA and tRNA molecules from the A site to the P site.<ref>{{Cite journal|last1=Salsi|first1=Enea|last2=Farah|first2=Elie|last3=Dann|first3=Jillian|last4=Ermolenko|first4=Dmitri N.|title=Following movement of domain IV of elongation factor G during ribosomal translocation|journal=Proceedings of the National Academy of Sciences|volume=111|issue=42|pages=15060–15065|doi=10.1073/pnas.1410873111|pmid=25288752|pmc=4210333|year=2014|bibcode=2014PNAS..11115060S|doi-access=free}}</ref>

The five domains may be also separated into two super-domains. Super-domain I consists of Domains I and II, and super-domain II consists of Domains III - IV. Throughout translocation, super-domain I will remain relatively unchanged, as it is responsible for binding tightly to the ribosome. However, super-domain II will undergo a large rotational motion from the pre-translocational (PRE) state to the post-translocational (POST) state. Super-domain I is similar to the corresponding sections of [[EF-Tu]].<ref>{{Cite journal|last1=Lin|first1=Jinzhong|last2=Gagnon|first2=Matthieu G.|last3=Bulkley|first3=David|last4=Steitz|first4=Thomas A.|title=Conformational Changes of Elongation Factor G on the Ribosome during tRNA Translocation|journal=Cell|volume=160|issue=1–2|pages=219–227|doi=10.1016/j.cell.2014.11.049|pmid=25594181|pmc=4297320|year=2015}}</ref><ref>{{Cite journal|last1=Li|first1=Wen|last2=Trabuco|first2=Leonardo G.|last3=Schulten|first3=Klaus|last4=Frank|first4=Joachim|date=2011-05-01|title=Molecular dynamics of EF-G during translocation|journal=Proteins: Structure, Function, and Bioinformatics|language=en|volume=79|issue=5|pages=1478–1486|doi=10.1002/prot.22976|pmid=21365677|issn=1097-0134|pmc=3132869}}</ref><ref>{{Cite journal|last1=Zhang|first1=Dejiu|last2=Yan|first2=Kaige|last3=Zhang|first3=Yiwei|last4=Liu|first4=Guangqiao|last5=Cao|first5=Xintao|last6=Song|first6=Guangtao|last7=Xie|first7=Qiang|last8=Gao|first8=Ning|last9=Qin|first9=Yan|title=New insights into the enzymatic role of EF-G in ribosome recycling|journal=Nucleic Acids Research|volume=43|issue=21|pages=10525–33|doi=10.1093/nar/gkv995|pmid=26432831|pmc=4666400|year=2015}}</ref> Super-domain II in the POST state mimics the tRNA molecule of the [[EF-Tu]] • GTP • aa-tRNA [[ternary complex]].<ref>{{Cite journal|last1=Nyborg|first1=J.|last2=Nissen|first2=P.|last3=Kjeldgaard|first3=M.|last4=Thirup|first4=S.|last5=Polekhina|first5=G.|last6=Clark|first6=B. F.|date=March 1996|title=Structure of the ternary complex of EF-Tu: macromolecular mimicry in translation|journal=Trends in Biochemical Sciences|volume=21|issue=3|pages=81–82|issn=0968-0004|pmid=8882578|doi=10.1016/S0968-0004(96)30008-X}}</ref>
[[File:EF-G Post State PDB 4V5F (labeled).jpg|thumb|Crystal structure of EF-G in the POST state with Domains I - V labeled. PDB ID: 4V5F|left]]

=== EF-G on the ribosome ===
==== Binding to L7/L12 ====
[[Ribosomal protein|L7/L12]] is only a multicopy protein on the [[Prokaryotic large ribosomal subunit|large ribosomal subunit]] of the bacterial ribosome that binds to certain GTPases, like [[Prokaryotic initiation factor-2|Initiation Factor 2]], [[EF-Tu|Elongation factor-Tu]], Release Factor 3, and  EF-G.<ref>{{Cite journal|last1=Mandava|first1=C. S.|last2=Peisker|first2=K.|last3=Ederth|first3=J.|last4=Kumar|first4=R.|last5=Ge|first5=X.|last6=Szaflarski|first6=W.|last7=Sanyal|first7=S.|date=2011-11-18|title=Bacterial ribosome requires multiple L12 dimers for efficient initiation and elongation of protein synthesis involving IF2 and EF-G|journal=Nucleic Acids Research|volume=40|issue=5|pages=2054–2064|doi=10.1093/nar/gkr1031|pmid=22102582|pmc=3299993|issn=0305-1048}}</ref> Specifically, the C-terminal of L7/L12 will bind to EF-G and is necessary for GTP hydrolysis.<ref name=":1" />

==== Interaction with the GTPase Associated Center ====
The GTPase Associated Center (GAC) is a region on the large ribosomal subunit that consists of two smaller regions of 23S ribosomal RNA called the L11 stalk and the sarcin-ricin loop (SRL).<ref>Maklan, E. J. (2012). Genetic and Biochemical Analysis of the GTPase Associated Center of the Ribosome. ''UC Santa Cruz''. Merritt ID: ark:/13030/m5js9t4d. Retrieved from https://escholarship.org/uc/item/7gh9v43h</ref> As a highly conserved rRNA loop in evolution, the SRL is critical in helping GTPases bind to the ribosome, but is not essential for GTP hydrolysis. There is some evidence to support that a phosphate oxygen in the A2662 residue of the SRL may help hydrolyze GTP.<ref>{{Cite journal|last1=Shi|first1=Xinying|last2=Khade|first2=Prashant K.|last3=Sanbonmatsu|first3=Karissa Y.|last4=Joseph|first4=Simpson|title=Functional Role of the Sarcin–Ricin Loop of the 23S rRNA in the Elongation Cycle of Protein Synthesis|journal=Journal of Molecular Biology|volume=419|issue=3–4|pages=125–138|doi=10.1016/j.jmb.2012.03.016|pmid=22459262|pmc=3348345|year=2012}}</ref>
[[File:EF-G, mRNA, and tRNAs in POST state PDB 4W29.gif|thumb|Animation of the 70S ribosome with the P site tRNA (orange), E site tRNA (green), mRNA (yellow), and elongation factor G (red) in the POST state. PDB ID: 4W29]]

== Function in protein elongation ==
EF-G catalyzes the translocation of the tRNA and mRNA down the ribosome at the end of each round of polypeptide elongation.<ref name=shoji /> In this process, the [[peptidyl transferase]] center (PTC) has catalyzed the formation of a peptide bond between amino acids, moving the polypeptide chain from the P site tRNA to the A site tRNA. The 50S and 30S ribosomal subunits are now allowed to rotate relative to each other by approximately 7°.<ref name=":2" /><ref>{{Cite journal|last1=Guo|first1=Z.|last2=Noller|first2=H. F.|title=Rotation of the head of the 30S ribosomal subunit during mRNA translocation|journal=Proceedings of the National Academy of Sciences|volume=109|issue=50|pages=20391–20394|doi=10.1073/pnas.1218999109|pmid=23188795|pmc=3528506|year=2012|bibcode=2012PNAS..10920391G|doi-access=free}}</ref> The subunit rotation is coupled with the movement of the 3' ends of both tRNA molecules on the large subunit from the A and P sites to the P and E sites, respectively, while the anticodon loops remain unshifted. This rotated ribosomal intermediate, in which the first tRNA occupies a hybrid A/P position and the second tRNA occupies a hybrid P/E position is a substrate for EF-G-GTP.<ref name="shoji" /><ref name=":2">{{Cite journal|last1=Choi|first1=Junhong|last2=Puglisi|first2=Joseph D.|title=Three tRNAs on the ribosome slow translation elongation|journal=Proceedings of the National Academy of Sciences|volume=114|issue=52|pages=13691–13696|doi=10.1073/pnas.1719592115|pmid=29229848|pmc=5748233|year=2017|doi-access=free}}</ref>

As a [[GTPase]], EF-G binds to the rotated ribosome near the A site in its GTP-bound state, and hydrolyzes GTP, releasing GDP and inorganic phosphate:

: <chem>GTP + H2O -> GDP + P_{i}</chem>

The hydrolysis of GTP allows for a large conformational change within EF-G, forcing the A/P tRNA to fully occupy the P site, the P/E tRNA to fully occupy the E site (and exit the ribosome complex), and the mRNA to shift three nucleotides down relative to the ribosome. The GDP-bound EF-G molecule then dissociates from the complex, leaving another free A-site where the elongation cycle can start again.<ref name="shoji" /><ref>{{cite journal|last1=da Cunha|first1=CE|last2=Belardinelli|first2=R|last3=Peske|first3=F|last4=Holtkamp|first4=W|last5=Wintermeyer|first5=W|last6=Rodnina|first6=MV|title=Dual use of GTP hydrolysis by elongation factor G on the ribosome|journal=Translation|date=2013|doi=10.4161/trla.24315|pmid=26824016|volume=1|issue=1|pages=e24315|pmc=4718068}}</ref>
[[File:EF-G and tRNAs in the POST state.jpg|thumb|Crystal structure of the ribosome with two tRNAs (orange and green) and EF-G (in cyan) after translocation. PDB ID: 4W29.]]

== Function in protein termination ==
Protein elongation continues until a [[stop codon]] appears on the mRNA. A Class I [[Prokaryotic release factors|release factor]] (RF1 or RF2) binds to the stop codon, which induces hydrolysis of the tRNA-peptide bond in the P site, allowing the newly-formed protein to exit the ribosome. The nascent peptide continues to fold and leaves the 70S ribosome, the mRNA, the deacylated tRNA (P site), and the Class I release factor (A site).<ref name=":0">{{Cite journal|last1=Das|first1=Debasis|last2=Samanta|first2=Dibyendu|last3=Bhattacharya|first3=Arpita|last4=Basu|first4=Arunima|last5=Das|first5=Anindita|last6=Ghosh|first6=Jaydip|last7=Chakrabarti|first7=Abhijit|last8=Gupta|first8=Chanchal Das|date=2017-01-18|title=A Possible Role of the Full-Length Nascent Protein in Post-Translational Ribosome Recycling|journal=PLOS ONE|language=en|volume=12|issue=1|pages=e0170333|doi=10.1371/journal.pone.0170333|pmid=28099529|pmc=5242463|issn=1932-6203|bibcode=2017PLoSO..1270333D|doi-access=free}}</ref><ref>{{Cite journal| doi=10.1016/j.molcel.2005.05.016|vauthors=Zavialov AV, Hauryliuk VV, Ehrenberg M | title=Splitting of the posttermination ribosome into subunits by the concerted action of RRF and EF-G| journal=Molecular Cell| year=2005| volume=18| issue=6| pages=675–686| pmid = 15949442 | doi-access=free}}</ref>

In a GTP-dependent manner, the subsequent recycling is catalyzed by a Class II release factor named RF3/prfC, [[Ribosome recycling factor]] (RRF), [[Prokaryotic initiation factor-3|Initiation Factor 3]] (IF3) and EF-G. The protein RF3 releases the Class I release factor so that it may occupy the ribosomal A site. EF-G hydrolyzes GTP and undergoes a large conformational change to push RF3 down the ribosome, which occurs alongside tRNA dissociation and promotes the ribosomal subunit rotation. This motion actively splits the B2a/B2b bridge, which connects the 30S and the 50S subunits, so that the ribosome can split.<ref name=":0" /> IF3 then isolates the 30S subunit to prevent re-association of the large and small subunits.<ref>{{Cite journal|last1=Hirokawa|first1=Go|last2=Nijman|first2=Romana M.|last3=Raj|first3=V. Samuel|last4=Kaji|first4=Hideko|last5=Igarashi|first5=Kazuei|last6=Kaji|first6=Akira|date=2005-08-01|title=The role of ribosome recycling factor in dissociation of 70S ribosomes into subunits|journal=RNA|language=en|volume=11|issue=8|pages=1317–1328|doi=10.1261/rna.2520405|issn=1355-8382|pmid=16043510|pmc=1370814}}</ref>

==Clinical significance==
EF-G in [[pathogenic bacteria]] can be inhibited by [[antibiotics]] that prevent EF-G from binding to the ribosome,<ref name=":4">{{Cite journal|last1=Walter|first1=Justin D.|last2=Hunter|first2=Margaret|last3=Cobb|first3=Melanie|last4=Traeger|first4=Geoff|last5=Spiegel|first5=P. Clint|date=2012-01-01|title=Thiostrepton inhibits stable 70S ribosome binding and ribosome-dependent GTPase activation of elongation factor G and elongation factor 4|journal=Nucleic Acids Research|language=en|volume=40|issue=1|pages=360–370|doi=10.1093/nar/gkr623|pmid=21908407|pmc=3245911|issn=0305-1048}}</ref> carrying out translocation<ref name=":5">{{Cite journal|last1=Bulkley|first1=David|last2=Brandi|first2=Letizia|last3=Polikanov|first3=Yury S.|last4=Fabbretti|first4=Attilio|last5=O’Connor|first5=Michael|last6=Gualerzi|first6=Claudio O.|last7=Steitz|first7=Thomas A.|title=The Antibiotics Dityromycin and GE82832 Bind Protein S12 and Block EF-G-Catalyzed Translocation|journal=Cell Reports|volume=6|issue=2|pages=357–365|doi=10.1016/j.celrep.2013.12.024|pmid=24412368|pmc=5331365|year=2014}}</ref> or dissociating from the ribosome.<ref name=":3">{{Cite journal|last1=Belardinelli|first1=Riccardo|last2=Rodnina|first2=Marina V.|date=2017-09-05|title=Effect of Fusidic Acid on the Kinetics of Molecular Motions During EF-G-Induced Translocation on the Ribosome|journal=Scientific Reports|language=En|volume=7|issue=1|pages=10536|doi=10.1038/s41598-017-10916-8|pmid=28874811|pmc=5585275|issn=2045-2322|bibcode=2017NatSR...710536B}}</ref>

For example, the antibiotic [[thiostrepton]] prevents EF-G from binding stably to the ribosome,<ref name=":4" /> while the antibiotics dityromycin and GE82832 inhibit the activity of EF-G by preventing the translocation of the A site tRNA. Dityromycin and GE82832 do not affect the binding of EF-G to the ribosome, however.<ref name=":5" />

The antibiotic [[fusidic acid]] is known to inhibit ''[[Staphylococcus aureus]]'' and other [[bacteria]] by binding to EF-G after one translocation event on the ribosome, preventing EF-G from dissociating.<ref name=":3" /><ref>{{Cite journal|last1=Koripella|first1=Ravi Kiran|last2=Chen|first2=Yang|last3=Peisker|first3=Kristin|last4=Koh|first4=Cha San|last5=Selmer|first5=Maria|last6=Sanyal|first6=Suparna|title=Mechanism of Elongation Factor-G-mediated Fusidic Acid Resistance and Fitness Compensation inStaphylococcus aureus|journal=Journal of Biological Chemistry|volume=287|issue=36|pages=30257–30267|doi=10.1074/jbc.m112.378521|pmid=22767604|pmc=3436278|year=2012|doi-access=free}}</ref> However, some bacterial strains have developed resistance to fusidic acid due to [[point mutation]]s in the ''fusA'' gene, which prevents fusidic acid from binding to EF-G.<ref name="pmid15935566">{{cite journal |vauthors=Macvanin M, Hughes D |title=Hyper-susceptibility of a fusidic acid-resistant mutant of Salmonella to different classes of antibiotics |journal=FEMS Microbiology Letters |volume=247 |issue=2 |pages=215–20 |date=June 2005 |pmid=15935566 |doi=10.1016/j.femsle.2005.05.007 |doi-access=free }}</ref><ref name="pmid10931308">{{cite journal |vauthors=Macvanin M, Johanson U, Ehrenberg M, Hughes D |title=Fusidic acid-resistant EF-G perturbs the accumulation of ppGpp |journal=Molecular Microbiology |volume=37 |issue=1 |pages=98–107 |date=July 2000 |pmid=10931308 |doi=10.1046/j.1365-2958.2000.01967.x |s2cid=10307058 |doi-access=free }}</ref>

==Evolution==
{{see also|GTPase#Translation factor family}}
EF-G has a complex evolutionary history, with numerous paralogous versions of the factor present in bacteria, suggesting subfunctionalization of different EF-G variants.<ref name=":6">{{Cite journal|author1=G C Atkinson |author2=S L Baldauf | title=Evolution of elongation factor G and the origins of mitochondrial and chloroplast forms| journal=Molecular Biology and Evolution| year=2011| volume=28| issue=3| pages=1281–92| pmid = 21097998| doi=10.1093/molbev/msq316 | doi-access=free}}</ref>

Elongation factors exist in all three [[Domain (biology)|domains]] of life with similar function on the ribosome. The [[Eukaryote|eukaryotic]] and [[Archaea|archeal]] homologs of EF-G are [[eEF2]] and aEF2, respectively. In bacteria (and some archaea), the ''fusA'' gene that encodes EF-G is found within the conserved ''str'' gene with the sequence 5′ - ''rpsL - rpsG - fusA - tufA'' - 3′.<ref name="Post 4660–4666"/> However, two other major forms of EF-G exist in some species of [[Spirochaetota|'''S'''pirochaetota]], [[Planctomycetota|'''P'''lanctomycetota]], and δ-'''P'''roteobacteria (which has since been split and renamed [[Bdellovibrionota]], [[Myxococcota]], and [[Thermodesulfobacteriota]]), which form the '''spd''' group of bacteria that have elongation factors spdEFG1 and spdEFG2.<ref name=":6" /><ref name=":7">{{Cite journal|last1=Margus|first1=Tõnu|last2=Remm|first2=Maido|last3=Tenson|first3=Tanel|date=2011-08-04|title=A Computational Study of Elongation Factor G (EFG) Duplicated Genes: Diverged Nature Underlying the Innovation on the Same Structural Template|journal=PLOS ONE|language=en|volume=6|issue=8|pages=e22789|doi=10.1371/journal.pone.0022789|pmid=21829651|pmc=3150367|issn=1932-6203|bibcode=2011PLoSO...622789M|doi-access=free}}</ref>

From spdEFG1 and spdEFG2 evolved the mitochondrial elongation factors mtEFG1 ([[GFM1]]) and mtEFG2 ([[GFM2]]), respectively.<ref name=":6" /><ref name=":7" /> The two roles of EF-G in elongation and termination of protein translation are split amongst the mitochondrial elongation factors, with mtEFG1 responsible for translocation and mtEFG2 responsible for termination and ribosomal recycling with mitochondrial [[Ribosome recycling factor|RRF]].

== See also ==
* [[Prokaryotic elongation factors]]
* [[EF-Ts]] (elongation factor thermo stable)
* [[EF-Tu]] (elongation factor thermo unstable)
* [[Elongation factor P|EF-P]] (elongation factor P)
* [[eEF2]] (eukaryotic elongation factor 2)
* [[Translation (biology)|Protein translation]]
* [[GTPase]]

==References==
{{reflist}}

== Further reading ==
* {{cite journal |last1=Carbone |first1=Christine E. |last2=Loveland |first2=Anna B. |last3=Gamper |first3=Howard B. |last4=Hou |first4=Ya-Ming |last5=Demo |first5=Gabriel |last6=Korostelev |first6=Andrei A. |title=Time-resolved cryo-EM visualizes ribosomal translocation with EF-G and GTP |journal=Nature Communications |date=December 2021 |volume=12 |issue=1 |pages=7236 |doi=10.1038/s41467-021-27415-0|doi-access=free|pmc=8668904 }}<!-- Might get integrated under "EF-G on the ribosome" some day -->

==External links==
* {{MeshName|Peptide+Elongation+Factor+G}}

{{GeneticTranslation}}
{{GTPases}}

[[Category:Protein biosynthesis]]