Protein Import and Routing Systems of Chloroplasts

Keegstra, Kenneth; Cline, Kenneth

doi:10.2307/3870884

Cited by 124 publications

(201 citation statements)

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“…Briefly, 20 g of purified, nucleotide-depleted atToc33G His or atToc33G His -G45R/K49N/S50R were bound to 8 l of packed Ni-NTA resin in the presence of 0.1 mM GTP or GMP-P(NH)P, and incubated with [1][2][3][4][5] Chloroplast Isolation and Toc159M Targeting Assays-Intact chloroplasts were isolated from ϳ2-week-old Arabidopsis thaliana (ecotype Wassilewskija) seedlings grown on 0.8% (w/v) phytagar plates containing Murashige and Skoog growth medium and 1% (w/v) sucrose, as described (15,22,23).…”

Section: Toc33/34 Mutations and Attoc159mentioning

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: Toc33/34 Mutations and Attoc159mentioning

confidence: 99%

“…The import of nucleus-encoded preproteins into chloroplasts is initiated by the translocon at the outer envelope membrane of chloroplasts (Toc) 1 (1)(2)(3). The Toc complex is comprised of three core subunits, Toc159 (4,5), Toc33/34 (6,7), and Toc75 (8 -10).…”

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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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“…11) suggest that pPORA does not interact with the previously identified translocons of the outer (Toc) and inner (Tic) chloroplast envelope (for review, see refs. [12][13][14].…”

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confidence: 99%

Identification of plastid envelope proteins required for import of protochlorophyllide oxidoreductase A into the chloroplast of barley

Reinbothe

Quigley

Gray

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

100

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Chloroplasts synthesize an abundance of different tetrapyrrole compounds. Among them are chlorophyll and its precursor protochlorophyllide (Pchlide), which accumulate in light-and dark-grown plants, respectively. Pchlide is converted to chlorophyllide by virtue of the NADPH:Pchlide oxidoreductase (POR), which, in angiosperms, is the only known light-dependent enzyme of the chlorophyll biosynthetic pathway. In etiolated barley plants, two closely related POR proteins exist termed PORA and PORB, which are nuclear gene products. Here we identified plastid envelope proteins that interact with the cytosolic PORA precursor (pPORA) during its posttranslational chloroplast import. We demonstrate that pPORA interacts with several previously unreported components. Among them is a Pchlide a oxygenase, which provides Pchlide b as import substrate for pPORA, and a tyrosine aminotransferase thought to be involved in the synthesis of photoprotective vitamin E. Two other constituents were found to be orthologs of the GTP-binding proteins Toc33͞34 and of the outer plastid envelope protein Oep16.

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“…These proteins are synthesized as precursors containing an N-terminal targeting signal, called the transit peptide, that mediates multiple steps in the import pathway (for reviews, see Refs. [1][2][3][4]. Whereas the chloroplast is unique to the plant cell, the mitochondrion and the endoplasmic reticulum (ER) 1 are two other major eukaryotic organelles that depend on massive protein translocation mediated by N-terminal targeting signals.…”

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confidence: 99%

“…[1][2][3][4]. Whereas the chloroplast is unique to the plant cell, the mitochondrion and the endoplasmic reticulum (ER) 1 are two other major eukaryotic organelles that depend on massive protein translocation mediated by N-terminal targeting signals. It has been predicted for Arabidopsis thaliana that up to 11,000 different precursor proteins may be targeted to these three organelles, ϳ3,500 to the chloroplast alone (5).…”

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Structural Properties of the Chloroplast Stromal Processing Peptidase Required for Its Function in Transit Peptide Removal

Richter

Lamppa

2003

Journal of Biological Chemistry

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The stromal processing peptidase (SPP) catalyzes removal of transit peptides from a diversity of precursor proteins imported into chloroplasts. SPP contains an HXXEH zinc-binding motif characteristic of members of the metallopeptidase family M16. We previously found that the three steps of precursor processing by SPP (i.e. transit peptide binding, removal, and conversion to a degradable subfragment) are mediated by features that reside in the C-terminal 10 -15 residues of the transit peptide. In this study, we performed a mutational analysis of SPP to identify structural elements that determine its function. SPP loses the ability to proteolytically remove the transit peptide when residues of the HXXEH motif, found in an N-terminal region, are mutated. Deletion of 240 amino acids from its C terminus also abolishes activity. Interestingly, however, SPP can still carry out the initial binding step, recognizing the Cterminal residues of the transit peptide. Hence, transit peptide binding and removal are two separable steps of the overall processing reaction. Transit peptide conversion to a subfragment also depends on the HXXEH motif. The precursor of SPP, containing an unusually long transit peptide itself, is not proteolytically active. Thus, the SPP precursor is synthesized as a latent form of the metallopeptidase.Chloroplast biogenesis and function depends on the import of a large diversity of proteins from the cytoplasm. These proteins are synthesized as precursors containing an N-terminal targeting signal, called the transit peptide, that mediates multiple steps in the import pathway (for reviews, see Refs. 1-4). Whereas the chloroplast is unique to the plant cell, the mitochondrion and the endoplasmic reticulum (ER) 1 are two other major eukaryotic organelles that depend on massive protein translocation mediated by N-terminal targeting signals. It has been predicted for Arabidopsis thaliana that up to 11,000 different precursor proteins may be targeted to these three organelles, ϳ3,500 to the chloroplast alone (5). Distinct properties of the targeting signals ensure organelle-specific sorting and translocation of the precursor proteins. Ultimately, highly specialized proteolytic enzymes that reside in each organelle remove the targeting signals (for a review, see Ref. 6).We have identified a general stromal processing peptidase (SPP) that removes transit peptides from an array of precursors involved in different biosynthetic pathways and destined for different chloroplast compartments (7). The activity of SPP, which is a soluble, monomeric enzyme, depends on metal ions (8). Analysis of a full-length SPP cDNA from pea revealed that the enzyme contains an HXXEH zinc-binding motif characteristic of members of the metallopeptidase family M16, such as pitrilysin, insulin-degrading enzyme, and the ␤-subunit of the mitochondrial processing peptidase (MPP) (9, 10). Conservation extends beyond the zinc-binding motif, where 25-30% identity is found in an N-terminal region of ϳ200 residues of SPP. The residues of the HXX...

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Protein Import and Routing Systems of Chloroplasts

Cited by 124 publications

References 0 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

Identification of plastid envelope proteins required for import of protochlorophyllide oxidoreductase A into the chloroplast of barley

Structural Properties of the Chloroplast Stromal Processing Peptidase Required for Its Function in Transit Peptide Removal

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