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

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.
Mesh Terms:
Amino Acid Motifs, Amino Acid Sequence, Arabidopsis, Arabidopsis Proteins, Binding Sites, Chloroplasts, Cytosol, GTP Phosphohydrolases, GTP-Binding Proteins, Green Fluorescent Proteins, Guanosine Triphosphate, Intracellular Membranes, Luminescent Proteins, Membrane Proteins, Molecular Sequence Data, Plants, Genetically Modified, Point Mutation, Protein Structure, Tertiary, Protein Transport, Recombinant Fusion Proteins, Sequence Alignment
J. Cell Biol.
Date: Dec. 09, 2002
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