PDBsum entry 3def

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Hydrolase PDB id
Protein chain
244 a.a. *
Waters ×206
* Residue conservation analysis
PDB id:
Name: Hydrolase
Title: Crystal structure of toc33 from arabidopsis thaliana, dimeri deficient mutant r130a
Structure: T7i23.11 protein. Chain: a. Fragment: gtp-domain, unp residues 1-251. Synonym: at1g02280, at1g02280/t7i23.11, attoc33 protein. Engineered: yes. Mutation: yes
Source: Arabidopsis thaliana. Mouse-ear cress,thale-cress. Organism_taxid: 3702. Gene: t7i23.11. Expressed in: escherichia coli. Expression_system_taxid: 562.
1.96Å     R-factor:   0.173     R-free:   0.213
Authors: P.Koenig,E.Schleiff,I.Sinning,I.Tews
Key ref: P.Koenig et al. (2008). On the significance of Toc-GTPase homodimers. J Biol Chem, 283, 23104-23112. PubMed id: 18541539
10-Jun-08     Release date:   24-Jun-08    
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Protein chain
Pfam   ArchSchema ?
O23680  (TOC33_ARATH) -  Translocase of chloroplast 33, chloroplastic
297 a.a.
244 a.a.*
Key:    PfamA domain  Secondary structure  CATH domain
* PDB and UniProt seqs differ at 1 residue position (black cross)

 Gene Ontology (GO) functional annotation 
  GO annot!
  Biochemical function     GTP binding     1 term  


J Biol Chem 283:23104-23112 (2008)
PubMed id: 18541539  
On the significance of Toc-GTPase homodimers.
P.Koenig, M.Oreb, K.Rippe, C.Muhle-Goll, I.Sinning, E.Schleiff, I.Tews.
Precursor protein translocation across the outer chloroplast membrane depends on the action of the Toc complex, containing GTPases as recognizing receptor components. The G domains of the GTPases are known to dimerize. In the dimeric conformation an arginine contacts the phosphate moieties of bound nucleotide in trans. Kinetic studies suggested that the arginine in itself does not act as an arginine finger of a reciprocal GTPase-activating protein (GAP). Here we investigate the specific function of the residue in two GTPase homologues. Arginine to alanine replacement variants have significantly reduced affinities for dimerization compared with wild-type GTPases. The amino acid exchange does not impact on the overall fold and nucleotide binding, as seen in the monomeric x-ray crystallographic structure of the Arabidopsis Toc33 arginine-alanine replacement variant at 2.0A. We probed the catalytic center with the transition state analogue GDP/AlF(x) using NMR and analytical ultracentrifugation. AlF(x) binding depends on the arginine, suggesting the residue can play a role in catalysis despite the non-GAP nature of the homodimer. Two non-exclusive functional models are discussed: 1) the coGAP hypothesis, in which an additional factor activates the GTPase in homodimeric form; and 2) the switch hypothesis, in which a protein, presumably the large Toc159 GTPase, exchanges with one of the homodimeric subunits, leading to activation.

Literature references that cite this PDB file's key reference

  PubMed id Reference
19187236 B.Agne, and F.Kessler (2009).
Protein transport in organelles: The Toc complex way of preprotein import.
  FEBS J, 276, 1156-1165.  
19010773 G.Rahim, S.Bischof, F.Kessler, and B.Agne (2009).
In vivo interaction between atToc33 and atToc159 GTP-binding domains demonstrated in a plant split-ubiquitin system.
  J Exp Bot, 60, 257-267.  
19744928 J.Lee, F.Wang, and D.J.Schnell (2009).
Toc receptor dimerization participates in the initiation of membrane translocation during protein import into chloroplasts.
  J Biol Chem, 284, 31130-31141.  
19335200 M.S.Sommer, and E.Schleiff (2009).
Molecular interactions within the plant TOC complex.
  Biol Chem, 390, 739-744.  
19806182 S.Meyer, S.Böhme, A.Krüger, H.J.Steinhoff, J.P.Klare, and A.Wittinghofer (2009).
Kissing G domains of MnmE monitored by X-ray crystallography and pulse electron paramagnetic resonance spectroscopy.
  PLoS Biol, 7, e1000212.
PDB codes: 3gee 3geh 3gei
19001421 T.Bionda, P.Koenig, M.Oreb, I.Tews, and E.Schleiff (2008).
pH sensitivity of the GTPase Toc33 as a regulatory circuit for protein translocation into chloroplasts.
  Plant Cell Physiol, 49, 1917-1921.  
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