Article Dans Une Revue Biochemical Journal Année : 2011

Substrate binding disrupts dimerization and induces nucleotide exchange of the chloroplast GTPase Toc33

Mislav Oreb
  • Fonction : Auteur
Anja Höfle
  • Fonction : Auteur
Patrick Koenig
  • Fonction : Auteur
Maik S Sommer
  • Fonction : Auteur
Irmgard Sinning
  • Fonction : Auteur
Fei Wang
Ivo Tews
  • Fonction : Auteur
Danny Schnell
  • Fonction : Auteur

Résumé

GTPases act as molecular switches to control many cellular processes, including signaling, protein translation and targeting. Switch activity can be regulated by external effector proteins or intrinsic properties, such as dimerization. The recognition and translocation of pre-proteins into chloroplasts (via the Translocator of the outer/inner envelope membrane of chloroplasts; TOC/TIC) is controlled by two homologous receptor GTPases, Toc33 and Toc159, whose reversible dimerization is proposed to regulate translocation of incoming proteins in a GTP dependent manner. Toc33 is a homodimerizing GTPase. Functional analysis suggests that homodimerization is a key step in the translocation process, the molecular functions of which as well as the elements regulating this event are largely unknown. Here, we show that homodimerization reduces the rate of nucleotide exchange, which is consistent with the observed orientation of the monomers in the crystal structure. Pre-protein binding induces a dissociation of the Toc33 homodimer and results in the exchange of GDP for GTP. Thus, homodimerization does not serve to activate the GTPase activity as manifold discussed but to control the nucleotide loading state. We discuss this novel regulatory mode and its impact on the current models of chloroplasts protein import.

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hal-00592570 , version 1 (13-05-2011)

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Mislav Oreb, Anja Höfle, Patrick Koenig, Maik S Sommer, Irmgard Sinning, et al.. Substrate binding disrupts dimerization and induces nucleotide exchange of the chloroplast GTPase Toc33. Biochemical Journal, 2011, 436 (2), pp.313-319. ⟨10.1042/BJ20110246⟩. ⟨hal-00592570⟩

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