A novel serine/proline-rich domain in combination with a transmembrane domain is required for the insertion of AtTic40 into the inner envelope membrane of chloroplasts.
AtTic40 is part of the chloroplastic protein import apparatus that is anchored in the inner envelope membrane by a single N-terminal transmembrane domain, and has a topology in which the bulk of the C-terminal domain is oriented toward the stroma. The targeting of AtTic40 to the inner envelope membrane involves two steps. Using an in vitro import assay, we showed that the sorting of AtTic40 requires a bipartite transit peptide, which was first cleaved by the stromal processing peptidase (SPP), thus generating a soluble AtTic40 stromal intermediate (iAtTic40). iAtTic40 was further processed by a second unknown peptidase, which generates its mature form (mAtTic40). Using deletion mutants, we identified a sequence motif N-terminal of the transmembrane domain that was essential for reinsertion of iAtTic40 into the inner envelope membrane. We have designated this region a serine/proline-rich (S/P-rich) domain and present a model describing its role in the targeting of AtTic40 to the inner envelope membrane.
Tripp
Joanna
J
MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48823, USA.
Inoue
Kentaro
K
Keegstra
Kenneth
K
Froehlich
John E
JE
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000032:analysis; D007425:Intracellular Membranes / Q000378:metabolism*; D008565:Membrane Proteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D008954:Models, Biological; D018832:Molecular Chaperones / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D016415:Sequence Alignment
D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D021382:Protein Sorting Signals; C476397:Tic40 protein, Arabidopsis; D049452:Green Fluorescent Proteins