Initial Binding of Preproteins Involving the Toc159 Receptor Can Be Bypassed during Protein Import into Chloroplasts

Chen, Kunhua; Chen, Xuejun; Schnell, Danny J.

doi:10.1104/pp.122.3.813

Cited by 114 publications

(116 citation statements)

References 28 publications

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“…Integration of [ 35 S]atToc159M into the outer membrane was assessed by treating equivalent samples of chloroplasts in the presence or absence of thermolysin. The ϳ52-kDa M-domain is protected from proteolysis upon proper integration of atToc159 (14,15,24). In the absence of any additions, atToc159M binds with low efficiency to isolated chloroplasts and remains protease sensitive (Fig.…”

Section: The Gtpase Activity Of Attoc33 Is Required For Attoc159mentioning

confidence: 99%

“…The Toc complex is comprised of three core subunits, Toc159 (4,5), Toc33/34 (6,7), and Toc75 (8 -10). Toc159 and Toc34 are homologous GTPases that recognize the transit peptides of preproteins (4 -7, 11-13) and regulate membrane translocation via a GTPase cycle (5,14,15). These two components associate with Toc75 to form a translocation pore across the outer membrane (8 -10).…”

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confidence: 99%

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The Roles of Toc34 and Toc75 in Targeting the Toc159 Preprotein Receptor to Chloroplasts

Wallas

Smith

Sánchez‐Nieto³

et al. 2003

Journal of Biological Chemistry

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The Toc complex at the outer envelope of chloroplasts initiates the import of nuclear-encoded preproteins from the cytosol into the organelle. The core of the Toc complex is composed of two receptor GTPases, Toc159 and Toc34, as well as Toc75, a ␤-barrel membrane channel. Toc159 is equally distributed between a soluble cytoplasmic form and a membrane-inserted form, suggesting that assembly of the Toc complex is dynamic. In the present study, we used the Arabidopsis thaliana orthologs of Toc159 and Toc34, atToc159 and atToc33, respectively, to investigate the requirements for assembly of the trimeric Toc complex. In addition to its intrinsic GTPase activity, we demonstrate that integration of atToc159 into the Toc complex requires atToc33 GTPase activity. Additionally, we show that the interaction of the two GTPase domains stimulates association of the membrane anchor of atToc159 with the translocon. Finally, we employ reconstituted proteoliposomes to demonstrate that proper insertion of the receptor requires both Toc75 and Toc34. Collectively these data suggest that Toc34 and Toc75 act sequentially to mediate docking and insertion of Toc159 resulting in assembly of the functional translocon.

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Section: The Gtpase Activity Of Attoc33 Is Required For Attoc159mentioning

confidence: 99%

mentioning

confidence: 99%

The Roles of Toc34 and Toc75 in Targeting the Toc159 Preprotein Receptor to Chloroplasts

Wallas

Smith

Sánchez‐Nieto³

et al. 2003

Journal of Biological Chemistry

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“…In pea, the Toc-complex consists of three major components forming a stable complex Ma et al, 1996). Toc159 (the number indicates the molecular mass in kD) and Toc34 are surface exposed, GTP-binding integral membrane proteins (Hirsch et al, 1994;Kessler et al, 1994;Seedorf et al, 1995;Chen et al, 2000a). The two proteins share a highly conserved GTP-binding domain .…”

Section: Introductionmentioning

confidence: 99%

“…The two proteins share a highly conserved GTP-binding domain . The available evidence indicates that the two proteins act in concert to recognize the chloroplast targeting peptide (Kouranov and Schnell, 1997;Sveshnikova et al, 2000;Chen et al, 2000a). Toc159 is thought to act as the primary receptor of transit sequences (Hirsch et al, 1994;Perry and Keegstra, 1994;Kouranov and Schnell, 1997).…”

Section: Introductionmentioning

confidence: 99%

“…In this group of proteins, the G-domain is flanked by an N-terminal A-domain (acidic domain) of unknown function. The A-and G-domains are both exposed to the cytosol (Chen et al, 2000a). A C-terminal Mdomain (membrane anchor domain) lacking predicted hydrophobic transmembrane helices anchors the proteins in the outer membrane (Hirsch et al, 1994;Kessler et al, 1994).…”

Section: Introductionmentioning

confidence: 99%

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AtToc90, a New GTP-Binding Component of the Arabidopsis Chloroplast Protein Import Machinery

et al. 2004

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AtToc159 is a GTP-binding chloroplast protein import receptor. In vivo, atToc159 is required for massive accumulation of photosynthetic proteins during chloroplast biogenesis. Yet, in mutants lacking atToc159 photosynthetic proteins still accumulate, but at strongly reduced levels whereas non-photosynthetic proteins are imported normally: This suggests a role for the homologues of atToc159 (atToc132, -120 and -90). Here, we show that atToc90 supports accumulation of photosynthetic proteins in plastids, but is not required for import of several constitutive proteins. Part of atToc90 associates with the chloroplast surface in vivo and with the Toc-complex core components (atToc75 and atToc33) in vitro suggesting a function in chloroplast protein import similar to that of atToc159. As both proteins specifically contribute to the accumulation of photosynthetic proteins in chloroplasts they may be components of the same import pathway.

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In Vitro Analysis of Chloroplast Protein Import

Smith¹,

Schnell²,

Fitzpatrick

et al. 2003

CP Cell Biology

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This unit describes protocols for isolating chloroplasts from pea (Pisum sativum) and Arabidopsis thaliana for the study of nuclear‐encoded plastid precursor proteins. Chloroplasts from both preparations are competent for the in vitro import of recombinant preproteins synthesized using in vitro translation systems derived from reticulocyte or wheat germ lysates. These assays can be used to test whether a particular protein is targeted to chloroplasts, for analyzing the suborganellar location of newly imported preproteins, or to study the mechanism of import itself.

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Initial Binding of Preproteins Involving the Toc159 Receptor Can Be Bypassed during Protein Import into Chloroplasts

Cited by 114 publications

References 28 publications

The Roles of Toc34 and Toc75 in Targeting the Toc159 Preprotein Receptor to Chloroplasts

The Roles of Toc34 and Toc75 in Targeting the Toc159 Preprotein Receptor to Chloroplasts

AtToc90, a New GTP-Binding Component of the Arabidopsis Chloroplast Protein Import Machinery

In Vitro Analysis of Chloroplast Protein Import

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