Essential role of the G-domain in targeting of the protein import receptor atToc159 to the chloroplast outer membrane

J Cell Biol. 2002 Dec 9;159(5):845-54. doi: 10.1083/jcb.200208018. Epub 2002 Dec 2.


Two homologous GTP-binding proteins, atToc33 and atToc159, control access of cytosolic precursor proteins to the chloroplast. atToc33 is a constitutive outer chloroplast membrane protein, whereas the precursor receptor atToc159 also exists in a soluble, cytosolic form. This suggests that atToc159 may be able to switch between a soluble and an integral membrane form. By transient expression of GFP fusion proteins, mutant analysis, and biochemical experimentation, we demonstrate that the GTP-binding domain regulates the targeting of cytosolic atToc159 to the chloroplast and mediates the switch between cytosolic and integral membrane forms. Mutant atToc159, unable to bind GTP, does not reinstate a green phenotype in an albino mutant (ppi2) lacking endogenous atToc159, remaining trapped in the cytosol. Thus, the function of atToc159 in chloroplast biogenesis is dependent on an intrinsic GTP-regulated switch that controls localization of the receptor to the chloroplast envelope.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Binding Sites
  • Chloroplasts / genetics
  • Chloroplasts / metabolism*
  • Cytosol / metabolism
  • GTP Phosphohydrolases / chemistry*
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism*
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / metabolism
  • Green Fluorescent Proteins
  • Guanosine Triphosphate / metabolism
  • Intracellular Membranes / metabolism*
  • Luminescent Proteins / metabolism
  • Membrane Proteins / chemistry*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Plants, Genetically Modified
  • Point Mutation
  • Protein Structure, Tertiary
  • Protein Transport
  • Recombinant Fusion Proteins / metabolism
  • Sequence Alignment


  • Arabidopsis Proteins
  • Luminescent Proteins
  • Membrane Proteins
  • Recombinant Fusion Proteins
  • TOC159 protein, Arabidopsis
  • Green Fluorescent Proteins
  • Guanosine Triphosphate
  • GTP Phosphohydrolases
  • GTP-Binding Proteins

Associated data

  • GENBANK/X14564