Cycle of Peptide Bond Formation Consumes Two Molecules of GTP and One Molecule of ATP

Let us conclude our discussion of elongation with a simple cost accounting. Mow many molecules of nucleoside triphosphate does it cost per round of peptide bond formation (leaving aside the energetics of amino acid biosynthesis and the energetics of initiation and termination)? As you will recall, one molecule of nucleoside triphosphate (ATP) is consumed by the aminoacyl-tRNA synthetase in creating the high-energy acyl bond lhat links the amino acid to the tRNA. The breakage of this high-energy bond drives the peptidyl transferase reac-

lion that creates the peptide bond. A second molecule of nucleoside triphosphate (GTP) is consumed in the delivery of a charged tRNA to the A site of the ribosome by FF-Tu and in ensuring that correct codon-anticodon recognition had taken place. Finally, a third nucleoside triphosphate is consumed in the EF-G-mediated process of translocation. Thus, making a peptide bond costs the cell two molecules of GTP and one of ATP, with one nucleoside triphosphate being consumed for each step in the translation elongation process. Interestingly, of the three molecules, only one (ATP) is energetically connected to peptide bond formation. The energy of the other two molecules (GTP) is spent to ensure the accuracy and order of events during translation (see Box 14-3, CTP-Binding Proteins, Conformational Switching, and the Fidelity and Ordering of the Events of Translation).

Throughout the discussion of translation elongation we have nol distinguished between prokaryotes and eukaryotes. Although the eukaryotic factors analogous to EF-Tu (eEFl) and EF'-G (eEF'2) are named differently, their functions are remarkably similar to their prokaryotic counterparts.

Box 14-3 GTP-Binding Proteins, Conformational Switching, and the Fidelity and Ordering of the Events of Translation

G1P is used throughout translation to control key events. The energy of GTP hydrolysis is not coupled to chemical modification as ATP is in the coupling of ammo acids to tRNAs. Instead, the energy of GTP hydrolysis is used to control the order and fidelity of events during translation. How is this accomplished?

A key feature of the GTP-binding proteins involved in translation is that that conformation changes depending on the guanine nucleotide (such as GDP vs GTP) to which they are bound. This can be seen for EF-Tu in Box 14-3 Figure 1, which shows the three-dimensional structure of EF-Tu bound to GTP or GDP EF-Tu undergoes a major conformational change when it binds to GTP that results in the formation of its tRNA binding site, in particular, one domain of ET-Tu (shown in magenta in Box 14-3 Figure 1) shifts its location relative to the other domains of the protein depending on the nucleotide that is bound This change in domain location as well as changes in the conformation of the other two domains (shown in turquoise and dark blue) results in the loima-tion of a new surface on EF-Tu that binds tightly to charged (RNAs (you can see EF-Tu bound to a tRNA in Figure 14-35). Thus, depending on the form of guanine nucleotide bound, these fa clots can have different functions or bind to different proteins/RNAs. For example, EFTu-GTp can bind to an aminoacyl-tRNA but EF-Tu-GDP cannot.

By coupling GTP hydrolysis to the completion of key events in translation, the order of these events can be tightly controlled. For EF-Tu, the GFP-dependent association of EF-Tu wilh amtnoacyl-iRNAs ensures that peptide bond formation does not occur prior to correct codon-anticodon pairing Formation of the correct base pairs triggers GTP hydrolysis. Once bound to GDP, EF-Tu is re leased from the aminoacyl-tRNA allowing peptide bond formation to ensue.

The mechanism that activates GTP hydrolysis by each of the GTP-regulated auxiliary proteins is the same. In each case, GTPase activity is stimulated through an interaction with a spedfic region of Öle targe subunit called the factor binding center. This interaction is not of suffident affinity to occur tn isolation. Instead, each CTP-controlted, translation factor must make several other critical interactions with the ribosome to stabilize the precise association with the factor binding center that leads to GTPase activation Indeed, as we have seen for tF-Tu, this interaction is highly sensitive to the exact nature of the interactions between EF-Tu, the aminoacyl-tRNA, the mRNA, and the ribosome. Thus, the interaction with the factor binding center monitors all the other interactions of these proteins and RNAs with the nbosorne. Oily when an appropriate set of interactions is achieved (such as correct codon-anticodon pairing) does the GTP-binding site able to interact productively with the factor binding center, leading to Gl P hydrolysis and the associated changes in protein conformation.

The use of GTP during translation is analogous to the use of ATP by the sliding damp loaders (see Chapter 8, Box 8-2) Recall that in that case, AfP binding was required to assemble an initial complex with the sliding damp, but AT P hydrolysis and release of the sliding damp could only occur when the damp loader encircled the pnma template junction. In translation, GTP is lequned for the initial assooation with the ribosome (and in some instances other RNAs and proteins), and GTP hydrolysis only occurs once the factor has correctly interacted with the ribosome. As in the case of the sliding damp, GTP hydrolysis generally results in the release of the factor from the ribosome.

Dibujos Amor

BOX 14-3 F ( C U R E 1 Comparison of EF-ïu bound to GDP and CTP. (a) EF-Tu bound to GDP. (b) EF-Tu bound to GTP. The GTP binding domain is shown tn red. The rotation of the magenta domain and the changes in the structure of the green and blue domains lead to the formation of a strong tRNA binding site when GTPis bound {see Figure 14 35). (Structure (a) Polekhina G., Thirup S., Kfeldgaard M., Nissen P.. Lippmann C. and Nybojg J. 1996. Structure 4: l ¡41 (b) Kjeldgard ML, Nissen P, Thirup $., and Nyborg i. 1993. Structure 1: 35 ) Images prepared with MolScript, BobScnpt and Raster 3D.

Box 14-1 (Continued)

BOX 14-3 F ( C U R E 1 Comparison of EF-ïu bound to GDP and CTP. (a) EF-Tu bound to GDP. (b) EF-Tu bound to GTP. The GTP binding domain is shown tn red. The rotation of the magenta domain and the changes in the structure of the green and blue domains lead to the formation of a strong tRNA binding site when GTPis bound {see Figure 14 35). (Structure (a) Polekhina G., Thirup S., Kfeldgaard M., Nissen P.. Lippmann C. and Nybojg J. 1996. Structure 4: l ¡41 (b) Kjeldgard ML, Nissen P, Thirup $., and Nyborg i. 1993. Structure 1: 35 ) Images prepared with MolScript, BobScnpt and Raster 3D.

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Responses

  • Massimo Lucciano
    How many GTP used in one peptide bond formation?
    3 years ago
  • sylvie
    How much ATP required to make initial, peptide bond?
    3 years ago
  • Peony
    How two gtp are required during peptide formation?
    2 years ago
  • kimberly
    How many ATP and GTP are required for peptide bond formation?
    2 years ago
  • Tanja Palo
    How many GTPs are required for peptide bond formation?
    2 years ago
  • Jamie-leigh
    How many energy bonds are expended in formation of peptide bond?
    11 months ago
  • Eyob Kidane
    What are the number of atp and gtp molecules required for the synthesis of proteins?
    5 months ago
  • James Torres
    How much atp is used for each amino acid added to the protein chain?
    4 months ago
  • Bisrat
    How many numbers of ATPs are required to make one peptide bond?
    4 months ago

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