S
IPR031157

Tr-type G domain, conserved site

InterPro entry
Short nameG_TR_CS

Description

The P-loop guanosine triphosphatases (GTPases) control a multitude of biological processes, ranging from cell division, cell cycling, and signal transduction, to ribosome assembly and protein synthesis. GTPases exert their control by interchanging between an inactive GDP-bound state and an active GTP-bound state, thereby acting as molecular switches. The common denominator of GTPases is the highly conserved guanine nucleotide-binding (G) domain that is responsible for binding and hydrolysis of guanine nucleotides.

Translational GTPases (trGTPases) are a family of proteins in which GTPase activity is stimulated by the large ribosomal subunit. This family includes translation initiation, elongation, and release factors and contains four subfamilies that are widespread, if not ubiquitous, in all three superkingdoms
[1]
:


 * Prokaryotic initiation factor 2 (IF2) and the related eukaryotic initiation factor 5B (eIF5B), catalyze ribosomal subunit joining to form elongation- competent ribosomes
[2, 3]
.
 * Bacterial SelB and eukaryotic/archaeal gamma subunit of initiation factor 2 (eIF-2gamma), specifically recognise noncanonical tRNAs. SelB specifically recognises selenocysteylated tRNA(Sec) and eIF-2gamma initiator tRNA (Met-tRNA(i))
[4, 5]
.
 * Bacterial elongation factor Tu (EF-Tu) and its archaeal and eukaryotic counterpart elongation factor 1 (EF-1 alpha), bring the aminoacyl-tRNA into the A site of the ribosome
[6, 7]
.
 * Bacterial peptide elongation factor G (EF-G) and its counterpart in Eukarya and Archaea, EF-2, catalyse the translocation step of translation
[8, 9]
.


The basic topology of the tr-type G domain consists of a six-stranded central β-sheet surrounded by five α-helices. Helices alpha2, alpha3 and alpha4 are on one side of the sheet, whereas alpha1 and alpha5 are on the other
[5]
. GTP is bound by the CTF-type G domain in a way common for G domains involving five conserved sequence motifs termed G1-G5. The base is in contact with the NKxD (G4) and SAx (G5) motifs, and the phosphates of the nucleotide are stabilised by main- and side-chain interactions with the P loop GxxxxGKT (G1). The most severe conformational changes are observed for the two switch regions which contain the xT/Sx (G2) and DxxG (G3) motifs that function as sensors for the presence of the gamma-phosphate. A Mg(2+) ion is coordinated by six oxygen ligands with octahedral coordination geometry; two of the ligands are water molecules, two come from the beta- and gamma-phosphates, and two are provided by the side chains of G1 and G2 threonines.

This entry represents a conserved site in the tr-type G domain. It is on a G2-containing region that has been shown to be involved in a conformational change mediated by the hydrolysis of GTP to GDP.

References

1.Classification and evolution of P-loop GTPases and related ATPases. Leipe DD, Wolf YI, Koonin EV, Aravind L. J. Mol. Biol. 317, 41-72, (2002). View articlePMID: 11916378

2.Initiation factor 2 crystal structure reveals a different domain organization from eukaryotic initiation factor 5B and mechanism among translational GTPases. Eiler D, Lin J, Simonetti A, Klaholz BP, Steitz TA. Proc. Natl. Acad. Sci. U.S.A. 110, 15662-7, (2013). View articlePMID: 24029018

3.eIF5B employs a novel domain release mechanism to catalyze ribosomal subunit joining. Kuhle B, Ficner R. EMBO J. 33, 1177-91, (2014). View articlePMID: 24686316

4.Evolutionary relationship between translation initiation factor eIF-2gamma and selenocysteine-specific elongation factor SELB: change of function in translation factors. Keeling PJ, Fast NM, McFadden GI. J. Mol. Evol. 47, 649-55, (1998). View articlePMID: 9847405

5.Selenocysteine tRNA-specific elongation factor SelB is a structural chimaera of elongation and initiation factors. Leibundgut M, Frick C, Thanbichler M, Bock A, Ban N. EMBO J. 24, 11-22, (2005). View articlePMID: 15616587

6.Structure-based sequence alignment of elongation factors Tu and G with related GTPases involved in translation. Avarsson A. J. Mol. Evol. 41, 1096-104, (1995). PMID: 8587108

7.Lateral transfer of an EF-1alpha gene: origin and evolution of the large subunit of ATP sulfurylase in eubacteria. Inagaki Y, Doolittle WF, Baldauf SL, Roger AJ. Curr. Biol. 12, 772-6, (2002). View articlePMID: 12007424

8.The structure of elongation factor G in complex with GDP: conformational flexibility and nucleotide exchange. al-Karadaghi S, Aevarsson A, Garber M, Zheltonosova J, Liljas A. Structure 4, 555-65, (1996). View articlePMID: 8736554

9.A computational study of elongation factor G (EFG) duplicated genes: diverged nature underlying the innovation on the same structural template. Margus T, Remm M, Tenson T. PLoS ONE 6, e22789, (2011). View articlePMID: 21829651

Cross References

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