Journal
JOURNAL OF CELL BIOLOGY
Volume 154, Issue 4, Pages 719-729Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1083/jcb.200105149
Keywords
chloroplast; receptor; Tat pathway; signal peptide; twin arginine
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Funding
- NIGMS NIH HHS [R01 GM046951, R01 GM46951] Funding Source: Medline
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The thylakoid Delta pH-dependent pathway transports folded proteins with twin arginine-containing signal peptides. Identified components of the machinery include cpTatC, Hcf106, and Tha4. The reaction occurs in two steps: precursor binding to the machinery, and transport across the membrane. Here, we show that a cpTatC-Hcf106 complex serves as receptor for specific binding of twin arginine-containing precursors. Antibodies to either Hcf106 or cpTatC, but not Tha4, inhibited precursor binding. Blue native gel electrophoresis and coimmunoprecipitation of digitonin-solubilized thylakoids showed that Hcf106 and cpTatC are members of an similar to 700-kD complex that lacks Tha4. Thylakoid-bound precursor proteins were also associated with an similar to 700-kD complex and were coimmunoprecipitated with antibodies to cpTatC or Hcf106. Chemical cross-linking revealed that precursors make direct contact with cpTatC and Hcf106 and confirmed that Tha4 is not associated with precursor, cpTatC, or Hcf106 in the membrane. Precursor binding to the cpTatC-Hcf106 complex required both the twin arginine and the hydrophobic core of the signal peptide. Precursors remained bound to the complex when Tha4 was sequestered by antibody, even in the presence of Delta pH. These results indicate that precursor binding to the cpTatC-Hcf106 complex constitutes the recognition event for this pathway and that subsequent participation by Tha4 leads to translocation.
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