Protein transport in organelles: Protein transport into and across the thylakoid membrane

Aldridge, Cassie; Cain, Peter; Robinson, Colin

doi:10.1111/j.1742-4658.2009.06875.x

Cited by 76 publications

(61 citation statements)

References 82 publications

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“…These may integrate into the thylakoid membrane without the aid of a proteinaceous machinery, as has been shown for several single-spanning nucleus-encoded proteins (reviewed in ref. 43). On the other hand, YidC is required to integrate the AtpH ortholog in bacteria, F o c (44), and it has been suggested that many short membrane proteins with C-terminal signal anchor sequences are posttranslationally integrated by the YidC translocon (45).…”

Section: Discussionmentioning

confidence: 99%

Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Zoschke

Barkan

2015

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

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Chloroplast genomes encode ∼37 proteins that integrate into the thylakoid membrane. The mechanisms that target these proteins to the membrane are largely unexplored. We used ribosome profiling to provide a comprehensive, high-resolution map of ribosome positions on chloroplast mRNAs in separated membrane and soluble fractions in maize seedlings. The results show that translation invariably initiates off the thylakoid membrane and that ribosomes synthesizing a subset of membrane proteins subsequently become attached to the membrane in a nucleaseresistant fashion. The transition from soluble to membraneattached ribosomes occurs shortly after the first transmembrane segment in the nascent peptide has emerged from the ribosome. Membrane proteins whose translation terminates before emergence of a transmembrane segment are translated in the stroma and targeted to the membrane posttranslationally. These results indicate that the first transmembrane segment generally comprises the signal that links ribosomes to thylakoid membranes for cotranslational integration. The sole exception is cytochrome f, whose cleavable N-terminal cpSecA-dependent signal sequence engages the thylakoid membrane cotranslationally. The distinct behavior of ribosomes synthesizing the inner envelope protein CemA indicates that sorting signals for the thylakoid and envelope membranes are distinguished cotranslationally. In addition, the fractionation behavior of ribosomes in polycistronic transcription units encoding both membrane and soluble proteins adds to the evidence that the removal of upstream ORFs by RNA processing is not typically required for the translation of internal genes in polycistronic chloroplast mRNAs.ribosome profiling | protein targeting | plastid | chloroplast | SecA

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Section: Discussionmentioning

confidence: 99%

Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Zoschke

Barkan

2015

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

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“…The other examples of folded protein transport are via nuclear pores; however, no such static structure has been seen on peroxisome membranes, suggesting the translocon is assembled on demand. The other example is the tat system in chloroplasts and bacteria; again, mechanistic details are lacking, but it has been proposed that variable copies of a membrane protein tatA are recruited to form a type of annulus around the folded protein (Aldridge et al, 2009). …”

Section: Translocation and Releasementioning

confidence: 99%

Getting a camel through the eye of a needle: the import of folded proteins by peroxisomes

Lanyon‐Hogg

Warriner

Baker

2010

Biology of the Cell

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Peroxisomes are a family of organelles which have many unusual features. They can arise de novo from the endoplasmic reticulum by a still poorly characterized process, yet possess a unique machinery for the import of their matrix proteins. As peroxisomes lack DNA, their function, which is highly variable and dependent on developmental and/or environmental conditions, is determined by the post-translational import of specific metabolic enzymes in folded or oligomeric states. The two classes of matrix targeting signals for peroxisomal proteins [PTS1 (peroxisomal targeting signal 1) and PTS2] are recognized by cytosolic receptors [PEX5 (peroxin 5) and PEX7 respectively] which escort their cargo proteins to, or possibly across, the peroxisome membrane. Although the membrane translocation mechanism remains unclear, it appears to be driven by thermodynamically favourable binding interactions. Recycling of the receptors from the peroxisome membrane requires ATP hydrolysis for two linked processes: ubiquitination of PEX5 (and the PEX7 co-receptors in yeast) and the function of two peroxisome-associated AAA (ATPase associated with various cellular activities) ATPases, which play a role in recycling or turnover of the ubiquitinated receptors. This review summarizes and integrates recent findings on peroxisome matrix protein import from yeast, plant and mammalian model systems, and discusses some of the gaps in our understanding of this remarkable protein transport system.

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“…S2). We suggest that these extremely short single-spanning membrane proteins, which integrate randomly into the thylakoid membrane in plants (30), would be difficult to transport to the thylakoid membrane if not encoded in the chloroplast genome.…”

Section: Mitochondrial Proteins Are Potential Targets For Recognitionmentioning

confidence: 99%

Mitochondrial genomes are retained by selective constraints on protein targeting

Björkholm

Harish

Hagström

et al. 2015

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

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Mitochondria are energy-producing organelles in eukaryotic cells considered to be of bacterial origin. The mitochondrial genome has evolved under selection for minimization of gene content, yet it is not known why not all mitochondrial genes have been transferred to the nuclear genome. Here, we predict that hydrophobic membrane proteins encoded by the mitochondrial genomes would be recognized by the signal recognition particle and targeted to the endoplasmic reticulum if they were nuclear-encoded and translated in the cytoplasm. Expression of the mitochondrially encoded proteins Cytochrome oxidase subunit 1, Apocytochrome b, and ATP synthase subunit 6 in the cytoplasm of HeLa cells confirms export to the endoplasmic reticulum. To examine the extent to which the mitochondrial proteome is driven by selective constraints within the eukaryotic cell, we investigated the occurrence of mitochondrial protein domains in bacteria and eukaryotes. The accessory protein domains of the oxidative phosphorylation system are unique to mitochondria, indicating the evolution of new protein folds. Most of the identified domains in the accessory proteins of the ribosome are also found in eukaryotic proteins of other functions and locations. Overall, one-third of the protein domains identified in mitochondrial proteins are only rarely found in bacteria. We conclude that the mitochondrial genome has been maintained to ensure the correct localization of highly hydrophobic membrane proteins. Taken together, the results suggest that selective constraints on the eukaryotic cell have played a major role in modulating the evolution of the mitochondrial genome and proteome. mitochondria | protein domain | evolution | endoplasmatic reticulum | signal recognition particle

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Protein transport in organelles: Protein transport into and across the thylakoid membrane

Cited by 76 publications

References 82 publications

Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Getting a camel through the eye of a needle: the import of folded proteins by peroxisomes

Mitochondrial genomes are retained by selective constraints on protein targeting

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