EF-Ts

EF-Ts (elongation factor thermo stable) is one of the prokaryotic elongation factors. It is found in human mitochrondria as TSFM. It is similar to eukaryotic EF-1B.

EF-Ts, bacterial
Identifiers
SymbolEF-Ts/EF-1B
InterProIPR001816
EF-Ts dimerisation domain
Identifiers
SymbolEF_TS
PfamPF00889
InterProIPR014039

EF-Ts serves as the guanine nucleotide exchange factor for EF-Tu (elongation factor thermo unstable), catalyzing the release of guanosine diphosphate from EF-Tu. This enables EF-Tu to bind to a new guanosine triphosphate molecule, release EF-Ts, and go on to catalyze another aminoacyl tRNA addition.[1]

Structure
EF-Ts and EF-Tu dimer forming the elongation factor complex full structure

The protein Qβ-Replicase is a tetrameric protein, meaning it contains four subunits. These subunits are the two elongation factors, EF-Tu & EF-Ts, the ribosomal protein subunit S1, and the RNA dependent RNA polymerase β-subunit. The two elongation factors form a heterodimer structure known as The Elongation factor complex, which is nessecary for the polymerization activity of the RDRP β-Subunit.[2] Its secondary structural components consists of α-helices, β-sheets and β-barrels.

EF-Ts comprises majority of the top portion of the protein, while EF-Tu makes up the bottom half where the beta barrels are seen. The conformation is considered to be open, when no guanine nucleotide is bound to the active site in EF-Tu. The EF-Ts chain contains four important domains, the C-terminal domain, N-terminal domain, Dimerization domain, and the Core domain which all play a specific role in the proteins structure and functionality. The dimerization domain contains four anti-parallel α-helices which is the main source of contact between EF-Tu and EF-Ts to form the dimer structure[3]

Domains
Domains of EF-Ts

The N-terminal domain spans from resides 1-54 (n1-n54), Core domain is from n55-n179, the Dimerization domain is from n180-n228, and lastly the C-terminal domain that is from n264-n282. the core domain contains two subdomains, C and N which interact with domains 3 and 1 of EF-Tu respectively.[4]

Elongation process pathway

EF-Ts functions as guanine nucleotide exchange factor, it catalyzes the reaction of EF-Tu*GDP ( inactive form) to EF-Tu*GTP (active). EF-Tu (active) then delivers the aminoacyl-tRNA to the ribosome. Therefore, EF-Ts main role is recycling EF-Tu back to its active state in order to complete another elongation cycle.

The majority of this pathway is performed through conformational changes of EF-Tu domain 1 which contains the active site and manipulation of the switch 1 & 2 regions by the ribosome and tRNA. First, in domain 1 of EF-Tu the GTPase activity site is blocked by a series of hydrophobic residues that block the catalytic residue His 84 in the inactive form prior to activation via EF-Ts.[5] Once the tRNA is bound to EF-Tu, it is then delivered to the Ribosome which hydrolyses the GTP leaving EF-Tu with a lower affinity to bind the tRNA. The ribosome does this through manipulation of the switch 1 region, after GTP hydrolysis the secondary structure switches from primarily α-helices to β-hairpin.[6] EF-Tu is then released from the ribosome in the inactive state completing the cycle until activated once again by EF-Ts.

Helix D of EF-Tu must interact with the N-terminal domain of EF-Ts for guanine nucleotide exchange. A recent study researched the reaction kinetics of the guanine nucleotide exchange by mutating certain residues on helix D of EF-Tu in order to see the primary residues involved in the pathway. Mutation of Leu148 and Glu 152 decreased the rate at which EF-Ts N-terminal domain binds to Helix D significantly, concluding these two residues play an important role in the reaction pathway.[7]

Amino acid conservation between organisms

This article focuses on EF-Ts as it exists in Qβ-Bacteriophage, however many organisms use a similar elongation process with proteins that have nearly the same function as EF-Ts. EF-Ts belongs to the group of proteins known as guanine nucleotide exchange factors and these proteins function in many different biochemical pathways, it also belongs to the tsf superfamily. Majority of the amino acid conservation seen between other organisms is located in the N-terminal domain where EF-Ts bind to EF-Tu and the guanine nucleotide exchange occurs. below is the alignment of the important N-Terminal domain of EF-Ts as it exists in other organisms.

  • E.Coli:    8-LVKELRERTGAGMMDCKKALT-20
  • LacBS:     8-LVAELRKRTEVSITKAREALS-20
  • Bos Taurus:8-LLMKLRRKTGYSFINCKKALE-20
  • Drosophila:8-ALAALRKKTGYTFANCKKALE-20

Conserved amino acids in all four are Leu12 and Arg18 (letters seen in bold above), it can be concluded that these two residues play an important role in the guanine nucleotide exchange since they are the only two completely conserved. In Eukaryotes EF-1 performs the same function, and the mechanism for guanine nucleotide exchange is nearly identical, as EF-Ts but is structurally dissimilar.[3]

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See also

References
  1. Kawashima T, Berthet-Colominas C, Wulff M, Cusack S, Leberman R (February 1996). "The structure of the Escherichia coli EF-Tu.EF-Ts complex at 2.5 A resolution". Nature. 379 (6565): 511–8. doi:10.1038/379511a0. PMID 8596629.
  2. Tomita K (September 2014). "Structures and functions of Qβ replicase: translation factors beyond protein synthesis". International Journal of Molecular Sciences. 15 (9): 15552–70. doi:10.3390/ijms150915552. PMC 4200798. PMID 25184952.
  3. Parker J (2001). "Elongation Factors; translation". Encylopedia of Genetics. pp. 610–611.
  4. Spremulli LL, Coursey A, Navratil T, Hunter SE (2004). "Initiation and elongation factors in mammalian mitochondrial protein biosynthesis". Progress in Nucleic Acid Research and Molecular Biology. 77: 211–61. doi:10.1016/S0079-6603(04)77006-3. ISBN 9780125400770. PMID 15196894.
  5. Schmeing TM, Voorhees RM, Kelley AC, Gao YG, Murphy FV, Weir JR, Ramakrishnan V (October 2009). "The crystal structure of the ribosome bound to EF-Tu and aminoacyl-tRNA". Science. 326 (5953): 688–694. Bibcode:2009Sci...326..688S. doi:10.1126/science.1179700. PMC 3763470. PMID 19833920.
  6. Schuette JC, Murphy FV, Kelley AC, Weir JR, Giesebrecht J, Connell SR, et al. (March 2009). "GTPase activation of elongation factor EF-Tu by the ribosome during decoding". The EMBO Journal. 28 (6): 755–65. doi:10.1038/emboj.2009.26. PMC 2666022. PMID 19229291.
  7. Wieden HJ, Gromadski K, Rodnin D, Rodnina MV (February 2002). "Mechanism of elongation factor (EF)-Ts-catalyzed nucleotide exchange in EF-Tu. Contribution of contacts at the guanine base". The Journal of Biological Chemistry. 277 (8): 6032–6. doi:10.1074/jbc.M110888200. PMID 11744709.
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