The transmembrane domain of AtToc64 and its C-terminal lysine-rich flanking region are targeting signals to the chloroplast outer envelope membrane [correction].
The targeting mechanism of chloroplast outer envelope membrane proteins remains largely unknown. We investigated the targeting of AtToc64. In protoplasts, the transmembrane domain (TMD) and its C-terminal Iysine-rich flanking region (LFR) were both necessary and sufficient for targeting to the outer envelope membrane. The lysine residues of the flanking region were critical; without the LFR, the TMD was targeted to the ER or the plasma membrane. In addition, the types of amino acid residues of the TMD, but not the amino acid sequence per se, is a signal for targeting to the chloroplast envelope membrane. TMDs containing phenylalanines were not targeted to the chloroplast in vivo. Based on these results, we propose that the chloroplast targeting signal of AtToc64 comprises two different components: 1) the LFR, which is a signal for evading SRP-mediated co-translational translocation and 2) the hydrophobic amino acid side chains of the TMD, whose size functions as a signal for a cytosolic factor that mediates transport to the chloroplast.
Lee
Yong Jik
YJ
Center for Plant Intracellular Trafficking, Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
Sohn
Eun Ju
EJ
Lee
Kwang Hee
KH
Lee
Dong Wok
DW
Hwang
Inhwan
I
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000737:chemistry / Q000378:metabolism*; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism; D008239:Lysine / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013347:Subcellular Fractions / Q000378:metabolism
D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; C488374:Toc64 protein, Arabidopsis; D008239:Lysine