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pH sensitivity of the GTPase Toc33 as a regulatory circuit for protein translocation into chloroplasts.

The properties of membrane-embedded GTPases are investigated to understand translocation of preprotein across the outer envelope of chloroplasts. The homo- and heterodimerization events of the GTPases had been established previously. We show that the hydrolytic activity of the GTPase Toc33 is pH insensitive in the homodimeric conformation but has a bell-shaped pH optimum in the monomeric conformation. Further, Toc33 GTPase homodimerization and protein translocation into chloroplasts are pH sensitive as well. pH sensitivity might serve to regulate translocation; alternatively, the documented pH sensitivity might reflect a mechanistic requirement for GTPase silencing during translocation as the GTPase switches between homo- and heterodimeric conformations.

Pubmed ID: 19001421


  • Bionda T
  • Koenig P
  • Oreb M
  • Tews I
  • Schleiff E


Plant & cell physiology

Publication Data

December 8, 2008

Associated Grants


Mesh Terms

  • Arabidopsis
  • Arabidopsis Proteins
  • Chloroplasts
  • GTP Phosphohydrolases
  • Hydrogen-Ion Concentration
  • Membrane Proteins
  • Protein Binding
  • Protein Multimerization
  • Protein Precursors
  • Protein Transport