Isolation of Components of the Chloroplast Protein Import Machinery

Schnell, Danny J.; Kessler, Félix; Blobel, Günter

doi:10.1126/science.7973649

Cited by 380 publications

(430 citation statements)

References 35 publications

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“…We further assume that the transport machinery involved in pPORA translocation could differ structurally from that required for import of pPORB and also from previously characterized plastid import complexes in that it might contain, in addition to previously identified membrane proteins (Hirsch et al, 1994 ;Kessler et al, 1994;Schnell et al, 1994) and lipids (Kerber and Soll, 1992;van't Hof et al, 1993), enzymes involved in chlorophyll (Matringe et al, 1992) and carotenoid biosynthesis (Markwell et al, 1992). Particularly interesting in this context is the observation that the target enzyme of norflurazon, phytoene desaturase (Chamovitz et al, 1991), as well as other enzymes involved in carotenoid biosynthesis are localized in the plastid envelope (Joyard et al, 1991).…”

Section: Summary and Perspectivesmentioning

confidence: 99%

The Regulation of Enzymes Involved in Chlorophyll Biosynthesis

Reinbothe

1996

European Journal of Biochemistry

125

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All living organisms contain tetrapyrroles. In plants, chlorophyll (chlorophyll a plus chlorophyll b) is the most abundant and probably most important tetrapyrrole. It is involved in light absorption and energy transduction during photosynthesis. Chlorophyll is synthesized from the intact carbon skeleton of glutamate via the C, pathway. This pathway takes place in the chloroplast. It is the aim of this review to summarize the current knowledge on the biochemistry and molecular biology of the C,-pathway enzymes, their regulated expression in response to light, and the impact of chlorophyll biosynthesis on chloroplast development. Particular emphasis will be placed on the key regulatory steps of chlorophyll biosynthesis in higher plants, such as 5-aminolevulinic acid formation, the production of Mg*+-protoporphyrin IX, and light-dependent protochlorophyllide reduction.

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Section: Summary and Perspectivesmentioning

confidence: 99%

The Regulation of Enzymes Involved in Chlorophyll Biosynthesis

Reinbothe

1996

European Journal of Biochemistry

125

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“…Such a coupled mechanism was observed for TIC40 in a time course of import (Li and Schnell, 2006). An experiment to test this idea was to conduct a bind-and-chase reaction, in which the binding step was one termed early intermediate of protein import (Schnell et al, 1994) and the chase and integration reaction were conducted with lysate obtained from the binding chloroplasts. This is shown in Figure 7 for both FTSH12 and SCY1.…”

Section: Ftsh12 Integrates Into Chloroplast Membranes In a Binding/chmentioning

confidence: 99%

Identification of Putative Substrates of SEC2, a Chloroplast Inner Envelope Translocase

Martin

Aldama

et al. 2017

Plant Physiol.

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Most chloroplast proteins are synthesized in the cytosol and imported into chloroplasts. Many imported proteins are further targeted to the thylakoid membrane and lumen by the SEC1, TAT, or SRP/ALB3 translocases. Others are targeted to the inner chloroplast envelope membrane by undescribed translocases. Recently, a second SEC system (SEC2) consisting of SCY2, SECE2, and SECA2 was found in the chloroplast envelope. Null mutants of SCY2 in Arabidopsis (Arabidopsis thaliana) exhibit a severe embryo-lethal phenotype. To investigate the function of the SEC2 system in plants, we used inducible RNA interference to knock down SCY2 in Arabidopsis. Seedlings cultured with inducer were chlorotic with aberrant chloroplasts and undeveloped thylakoids, indicating an essential role for SCY2 in chloroplast biogenesis beyond embryo development. In SCY2 down-regulated seedlings, several thylakoid membrane proteins, including SCY1, ALB3, and TATC, and inner envelope membrane proteins, including TIC40, TIC110, and FTSH12, were reduced substantially, suggesting that they may be SEC2 substrates. Additional insight was achieved by the in vitro reconstitution of protein integration into chloroplast membranes. The results show that SCY1 and ALB3 target directly to the thylakoid membrane and are likely independent of SEC2. FTSH12 was integrated into the envelope membrane in a coupled import-integration reaction that was impaired by the SECA inhibitor sodium azide. The stromal intermediate of TIC40 integrated into the envelope in a reaction that was largely inhibited when antibodies against epitope-tagged SCY2 or SECE2 were applied. These data demonstrate that the SEC2 translocase likely integrates a subset of inner envelope membrane proteins, such as FTSH12 and TIC40.

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“…The core components of the Toc complex are called Toc159, Toc34, and Toc75, according to their molecular weights (Hirsch et al, 1994;Kessler et al, 1994;Perry and Keegstra, 1994;Schnell et al, 1994;Seedorf et al, 1995;Bölter et al, 1998). Toc159 and Toc34 are related GTPases that have been proposed to act as preprotein receptors.…”

Section: Introductionmentioning

confidence: 99%

The Arabidopsisppi1Mutant Is Specifically Defective in the Expression, Chloroplast Import, and Accumulation of Photosynthetic Proteins[W]

et al. 2003

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The import of nucleus-encoded proteins into chloroplasts is mediated by translocon complexes in the envelope membranes. A component of the translocon in the outer envelope membrane, Toc34, is encoded in Arabidopsis by two homologous genes, atTOC33 and atTOC34 . Whereas atTOC34 displays relatively uniform expression throughout development, atTOC33 is strongly upregulated in rapidly growing, photosynthetic tissues. To understand the reason for the existence of these two related genes, we characterized the atTOC33 knockout mutant ppi1 . Immunoblotting and proteomics revealed that components of the photosynthetic apparatus are deficient in ppi1 chloroplasts and that nonphotosynthetic chloroplast proteins are unchanged or enriched slightly. Furthermore, DNA array analysis of 3292 transcripts revealed that photosynthetic genes are moderately, but specifically, downregulated in ppi1 . Proteome differences in ppi1 could be correlated with protein import rates: ppi1 chloroplasts imported the ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit and 33-kD oxygen-evolving complex precursors at significantly reduced rates, but the import of a 50S ribosomal subunit precursor was largely unaffected. The ppi1 import defect occurred at the level of preprotein binding, which is consistent with a role for atToc33 during preprotein recognition. The data suggest that atToc33 is involved preferentially in the import of photosynthetic proteins and, by extension, that atToc34 is involved in the import of nonphotosynthetic chloroplast proteins.

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Isolation of Components of the Chloroplast Protein Import Machinery

Cited by 380 publications

References 35 publications

The Regulation of Enzymes Involved in Chlorophyll Biosynthesis

The Regulation of Enzymes Involved in Chlorophyll Biosynthesis

Identification of Putative Substrates of SEC2, a Chloroplast Inner Envelope Translocase

The Arabidopsisppi1Mutant Is Specifically Defective in the Expression, Chloroplast Import, and Accumulation of Photosynthetic Proteins[W]

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