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A twin arginine signal peptide and the pH gradient trigger reversible assembly of the thylakoid [Delta]pH/Tat translocase.

Mori H, Cline K - J. Cell Biol. (2002)

Bottom Line: In contrast, Tha4 was only associated with cpTatC and Hcf106 in the presence of a functional precursor and the DeltapH.Such an assembly-disassembly cycle could explain how the DeltapH/Tat system can assemble translocases to accommodate folded proteins of varied size.It also explains in part how the system can exist in the membrane without compromising its ion and proton permeability barrier.

View Article: PubMed Central - PubMed

Affiliation: Horticultural Sciences and Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL 32611, USA. Britta.J.Eickholt@kcl.ac.uk

ABSTRACT
The thylakoid DeltapH-dependent/Tat pathway is a novel system with the remarkable ability to transport tightly folded precursor proteins using a transmembrane DeltapH as the sole energy source. Three known components of the transport machinery exist in two distinct subcomplexes. A cpTatC-Hcf106 complex serves as precursor receptor and a Tha4 complex is required after precursor recognition. Here we report that Tha4 assembles with cpTatC-Hcf106 during the translocation step. Interactions among components were examined by chemical cross-linking of intact thylakoids followed by immunoprecipitation and immunoblotting. cpTatC and Hcf106 were consistently associated under all conditions tested. In contrast, Tha4 was only associated with cpTatC and Hcf106 in the presence of a functional precursor and the DeltapH. Interestingly, a synthetic signal peptide could replace intact precursor in triggering assembly. The association of all three components was transient and dissipated upon the completion of protein translocation. Such an assembly-disassembly cycle could explain how the DeltapH/Tat system can assemble translocases to accommodate folded proteins of varied size. It also explains in part how the system can exist in the membrane without compromising its ion and proton permeability barrier.

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Working model for formation of active translocase of thylakoid ΔpH-dependent/Tat pathway. See text for details.
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fig4: Working model for formation of active translocase of thylakoid ΔpH-dependent/Tat pathway. See text for details.

Mentions: Here, we provided evidence for regulated assembly of the thylakoid ΔpH/Tat translocase. A working model for this process is presented in Fig. 4. The first step is reversible precursor binding to the cpTatC–Hcf106 receptor complex, which occurs in the presence or absence of the ΔpH (Fig. 4, binding step). Preliminary purification studies indicate that the precursor-bound receptor complex consists predominantly, if not entirely, of cpTatC, Hcf106, and precursor (unpublished data). Precursor binding may induce some structural alteration of this complex because binding is prerequisite for the second step, ΔpH-dependent recruitment of Tha4 to the receptor complex (Fig. 4, assembly step). Structural changes upon precursor binding have been shown for the translocase of the outer mitochondrial membrane (Rapaport et al., 1998). We also expect that the ΔpH induces a conformational change in some component(s) that triggers their association. Such a conformational change might result from protonation of lumen-proximal acidic residues of components, such as the conserved glutamate that is found in the transmembrane domain of both Hcf106 and Tha4 proteins (Mori and Cline, 2001). Conformational changes have been shown to accompany protonation and deprotonation of acidic residues in transmembrane domains of other proteins. An example is subunit c of the ATP synthase, where the induced structural change is related to the proton-driven rotation of the c12 disk (Rastogi and Girvin, 1999).


A twin arginine signal peptide and the pH gradient trigger reversible assembly of the thylakoid [Delta]pH/Tat translocase.

Mori H, Cline K - J. Cell Biol. (2002)

Working model for formation of active translocase of thylakoid ΔpH-dependent/Tat pathway. See text for details.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199252&req=5

fig4: Working model for formation of active translocase of thylakoid ΔpH-dependent/Tat pathway. See text for details.
Mentions: Here, we provided evidence for regulated assembly of the thylakoid ΔpH/Tat translocase. A working model for this process is presented in Fig. 4. The first step is reversible precursor binding to the cpTatC–Hcf106 receptor complex, which occurs in the presence or absence of the ΔpH (Fig. 4, binding step). Preliminary purification studies indicate that the precursor-bound receptor complex consists predominantly, if not entirely, of cpTatC, Hcf106, and precursor (unpublished data). Precursor binding may induce some structural alteration of this complex because binding is prerequisite for the second step, ΔpH-dependent recruitment of Tha4 to the receptor complex (Fig. 4, assembly step). Structural changes upon precursor binding have been shown for the translocase of the outer mitochondrial membrane (Rapaport et al., 1998). We also expect that the ΔpH induces a conformational change in some component(s) that triggers their association. Such a conformational change might result from protonation of lumen-proximal acidic residues of components, such as the conserved glutamate that is found in the transmembrane domain of both Hcf106 and Tha4 proteins (Mori and Cline, 2001). Conformational changes have been shown to accompany protonation and deprotonation of acidic residues in transmembrane domains of other proteins. An example is subunit c of the ATP synthase, where the induced structural change is related to the proton-driven rotation of the c12 disk (Rastogi and Girvin, 1999).

Bottom Line: In contrast, Tha4 was only associated with cpTatC and Hcf106 in the presence of a functional precursor and the DeltapH.Such an assembly-disassembly cycle could explain how the DeltapH/Tat system can assemble translocases to accommodate folded proteins of varied size.It also explains in part how the system can exist in the membrane without compromising its ion and proton permeability barrier.

View Article: PubMed Central - PubMed

Affiliation: Horticultural Sciences and Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL 32611, USA. Britta.J.Eickholt@kcl.ac.uk

ABSTRACT
The thylakoid DeltapH-dependent/Tat pathway is a novel system with the remarkable ability to transport tightly folded precursor proteins using a transmembrane DeltapH as the sole energy source. Three known components of the transport machinery exist in two distinct subcomplexes. A cpTatC-Hcf106 complex serves as precursor receptor and a Tha4 complex is required after precursor recognition. Here we report that Tha4 assembles with cpTatC-Hcf106 during the translocation step. Interactions among components were examined by chemical cross-linking of intact thylakoids followed by immunoprecipitation and immunoblotting. cpTatC and Hcf106 were consistently associated under all conditions tested. In contrast, Tha4 was only associated with cpTatC and Hcf106 in the presence of a functional precursor and the DeltapH. Interestingly, a synthetic signal peptide could replace intact precursor in triggering assembly. The association of all three components was transient and dissipated upon the completion of protein translocation. Such an assembly-disassembly cycle could explain how the DeltapH/Tat system can assemble translocases to accommodate folded proteins of varied size. It also explains in part how the system can exist in the membrane without compromising its ion and proton permeability barrier.

Show MeSH