atTic110 functions as a scaffold for coordinating the stromal events of protein import into chloroplasts.
The translocon of the inner envelope membrane of chloroplasts (Tic) mediates the late events in the translocation of nucleus-encoded preproteins into chloroplasts. Tic110 is a major integral membrane component of active Tic complexes and has been proposed to function as a docking site for translocation-associated stromal factors and as a component of the protein-conducting channel. To investigate the various proposed functions of Tic110, we have investigated the structure, topology, and activities of a 97.5-kDa fragment of Arabidopsis Tic110 (atTic110) lacking only the amino-terminal transmembrane segments. The protein was expressed both in Escherichia coli and Arabidopsis as a stable, soluble protein with a high alpha-helical content. Binding studies demonstrate that a region of the atTic110-soluble domain selectively associates with chloroplast preproteins at the late stages of membrane translocation. These data support the hypothesis that the bulk of Tic110 extends into the chloroplast stroma and suggest that the domain forms a docking site for preproteins as they emerge from the Tic translocon.
Inaba
Takehito
T
Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Li
Ming
M
Alvarez-Huerta
Mayte
M
Kessler
Felix
F
Schnell
Danny J
DJ
D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D002845:Chromatography; D002942:Circular Dichroism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D017353:Gene Deletion; D015151:Immunoblotting; D008565:Membrane Proteins / Q000737:chemistry* / Q000502:physiology*; D018532:Pisum sativum; D010940:Plant Proteins / Q000737:chemistry*; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D021381:Protein Transport
D029681:Arabidopsis Proteins; D003432:Cross-Linking Reagents; D018076:DNA, Complementary; D008565:Membrane Proteins; D010940:Plant Proteins; C499578:Tic110 protein, Arabidopsis