Unassisted membrane insertion as the initial step in DeltapH/Tat-dependent protein transport.
In the thylakoid membrane of chloroplasts as well as in the cytoplasmic membrane of bacteria, the DeltapH/Tat-dependent protein transport pathway is responsible for the translocation of folded proteins. Using the chimeric 16/23 protein as model substrate in thylakoid transport experiments, we dissected the transport process into several distinct steps that are characterized by specific integral translocation intermediates. Formation of the early translocation intermediate Ti-1, which still exposes the N and the C terminus to the stroma, is observed with thylakoids pretreated with (i) solutions of chaotropic salts or alkaline pH, (ii) protease, or (iii) antibodies raised against TatA, TatB, or TatC. Membrane insertion takes place even into liposomes, demonstrating that proteinaceous components are not required. This suggests that Tat-dependent transport may be initiated by the unassisted insertion of the substrate into the lipid bilayer, and that interaction with the Tat translocase takes place only in later stages of the process.
Hou
Bo
B
Institut für Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, D-06120 Halle (Saale), Germany.
Frielingsdorf
Stefan
S
Klösgen
Ralf Bernd
RB
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism*; D015696:Gene Products, tat / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D018532:Pisum sativum / Q000166:cytology; D011498:Protein Precursors / Q000378:metabolism; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism
D015696:Gene Products, tat; D008081:Liposomes; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins