Evolution and targeting of Omp85 homologs in the chloroplast outer envelope membrane

Day, Philip M; Potter, Daniel; Inoue, Kentaro

doi:10.3389/fpls.2014.00535

Cited by 45 publications

(67 citation statements)

References 78 publications

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“…2C). This α-helix insertion is unique to Toc75 and is not observed in BamA, Sam50, or OEP80 (17). The previously identified flanking cysteine residues (C256 and C300) were found in proximity to each other and ideally positioned to form a potential disulfide in vivo in the unstructured loop adjacent to the P2-helix, which may further stabilize the overall structure (17) (Fig.…”

Section: Resultsmentioning

confidence: 84%

“…This helix is not found in any of the BamA POTRAs (26,36,40) or POTRAs from Omp85 family members in the cyanobacteria Nostoc sp. PCC7120 and Thermosynechoccocus, both of which have structures available (17,49,50). In addition, based on sequence comparison, the insertion is unique to Toc75 relative to OEP80 and mitochondrial Sam50 (17).…”

Section: Discussionmentioning

confidence: 99%

“…Day et al (17) previously investigated the conservation of the Toc75 POTRA domains in plant species. The Arabidopsis Toc75 POTRA domains used in this study exhibited >61% sequence identity to TOC75 proteins from across the land plants, including the bryophytes (e.g., Physcomitrella patens) and vascular plants (17).…”

Section: Discussionmentioning

confidence: 99%

“…It was previously observed that POTRA1-3 interacts with the chloroplast precursor of the small subunit of Rubisco (preSSU) (15,17,41) in an in vitro solid-phase binding assay. The localization of the POTRA domains in the intermembrane space led to the proposal that they serve as docking sites for the preprotein as it is transported across the outer membrane (15,31).…”

Section: Potra2-3 Mediates An Interaction With the Model Chloroplastmentioning

confidence: 99%

“…In addition to Toc75, chloroplasts have an additional Omp85 family member, outer envelope protein 80 (OEP80). OEP80 is not found associated with core TOC/TIC complex components (14,15), and has diverged significantly in sequence from Toc75 (16,17), implying that it is not involved in protein import. The function of OEP80 remains unknown; however, it is essential for plant viability (18).…”

mentioning

confidence: 99%

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The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

O'Neil

Richardson

Paila

et al. 2017

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

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Protein trafficking across membranes is an essential function in cells; however, the exact mechanism for how this occurs is not well understood. In the endosymbionts, mitochondria and chloroplasts, the vast majority of proteins are synthesized in the cytoplasm as preproteins and then imported into the organelles via specialized machineries. In chloroplasts, protein import is accomplished by the TOC (translocon on the outer chloroplast membrane) and TIC (translocon on the inner chloroplast membrane) machineries in the outer and inner envelope membranes, respectively. TOC mediates initial recognition of preproteins at the outer membrane and includes a core membrane channel, Toc75, and two receptor proteins, Toc33/34 and Toc159, each containing GTPase domains that control preprotein binding and translocation. Toc75 is predicted to have a β-barrel fold consisting of an N-terminal intermembrane space (IMS) domain and a C-terminal 16-stranded β-barrel domain. Here we report the crystal structure of the N-terminal IMS domain of Toc75 from Arabidopsis thaliana, revealing three tandem polypeptide transportassociated (POTRA) domains, with POTRA2 containing an additional elongated helix not observed previously in other POTRA domains. Functional studies show an interaction with the preprotein, preSSU, which is mediated through POTRA2-3. POTRA2-3 also was found to have chaperone-like activity in an insulin aggregation assay, which we propose facilitates preprotein import. Our data suggest a model in which the POTRA domains serve as a binding site for the preprotein as it emerges from the Toc75 channel and provide a chaperonelike activity to prevent misfolding or aggregation as the preprotein traverses the intermembrane space.protein import | chloroplast | outer membrane | Toc75 | POTRA domain

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Section: Resultsmentioning

confidence: 84%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Potra2-3 Mediates An Interaction With the Model Chloroplastmentioning

confidence: 99%

mentioning

confidence: 99%

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The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

O'Neil

Richardson

Paila

et al. 2017

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

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Early stages in the biogenesis of eukaryotic β‐barrel proteins

Jores

Rapaport

2017

FEBS Letters

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The endosymbiotic organelles mitochondria and chloroplasts harbour, similarly to their prokaryotic progenitors, b-barrel proteins in their outer membrane. These proteins are encoded on nuclear DNA, translated on cytosolic ribosomes and imported into their target organelles by a dedicated machinery. Recent studies have provided insights into the import into the organelles and the membrane insertion of these proteins. Although the cytosolic stages of their biogenesis are less well defined, it is speculated that upon their synthesis, chaperones prevent b-barrel proteins from aggregation and keep them in an import-competent conformation. In this Review, we summarize the current knowledge about the biogenesis of b-barrel proteins, focusing on the early stages from the translation on cytosolic ribosomes to the recognition on the surface of the organelle.Keywords: chloroplasts; mitochondria; b-barrel proteins Mitochondria and chloroplasts are eukaryotic organelles that originated from the endosymbiotic uptake of an a-proteobacterium and a cyanobacterium, respectively [1]. During their evolution, most of the organellar proteins were transferred to the host cell's nucleus and the organelles underwent many changes to adapt to the new environment. Yet, both organelles retained several features of their prokaryotic progenitors, one of these being the occurrence of b-barrel proteins in the outer membrane. Of note, chloroplasts represent only one type of plant plastids; however, the other plastid types also contain b-barrel proteins. Since not much is known about the biogenesis pathways in the other plastids, we refer here to chloroplasts. Importantly, the outer membranes of mitochondria, chloroplasts and Gram-negative bacteria are the only membranes that contain b-barrel proteins. Such proteins span the membrane with a cylindrical b-sheet formed by 8-26 antiparallel b-strands, thereby forming a hydrophilic membrane pore.Whereas a vast number of different b-barrel proteins reside in the outer membranes of Gram-negative bacteria, only few of them exist in eukaryotes. Mitochondria from yeast and human cells contain five b-barrel proteins and nine b-barrel proteins were identified in Arabidopsis thaliana chloroplasts. Most b-barrel proteins, such as the mitochondrial voltage-dependent anion channel (VDAC; called Porin in yeast), and the chloroplast outer envelope protein 21 (OEP21), OEP24 and OEP37 function as transporters for ions, small molecules, peptides and nucleic acids. Another group of b-barrel proteins, including Tom40, Tob55/Sam50 and Toc75, play an essential role in the import of proteins into mitochondria and plastids. Furthermore, eukaryotic b-barrel proteins are also involved in a variety of cellular processes, including signalling, organelle interactions and apoptosis [2,3]. The targeting of b-barrel proteins to and their assembly into the outer membrane of chloroplasts and mitochondria is essential for the biogenesis, morphology and maintenance Abbreviations BAM, b-barrel assembly machinery; Mdm10, mitochondrial ...

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Toc75‐V/OEP80 is processed during translocation into chloroplasts, and the membrane‐embedded form exposes its POTRA domain to the intermembrane space

et al. 2020

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The insertion of membrane proteins requires proteinaceous complexes in the cytoplasm, the membrane, and the lumen of organelles. Most of the required complexes have been described, while the components for insertion of β‐barrel‐type proteins into the outer membrane of chloroplasts remain unknown. The same holds true for the signals required for the insertion of β‐barrel‐type proteins. At present, only the processing of Toc75‐III, the β‐barrel‐type protein of the central chloroplast translocon with an atypical signal, has been explored in detail. However, it has been debated whether Toc75‐V/ outer envelope protein 80 (OEP80), a second protein of the same family, contains a signal and undergoes processing. To substantiate the hypothesis that Toc75‐V/OEP80 is processed as well, we reinvestigated the processing in a protoplast‐based assay as well as in native membranes. Our results confirm the existence of a cleavable segment. By protease protection and pegylation, we observed intermembrane space localization of the soluble N‐terminal domain. Thus, Toc75‐V contains a cleavable N‐terminal signal and exposes its polypeptide transport‐associated domains to the intermembrane space of plastids, where it likely interacts with its substrates.

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Evolution and targeting of Omp85 homologs in the chloroplast outer envelope membrane

Cited by 45 publications

References 78 publications

The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

The POTRA domains of Toc75 exhibit chaperone-like function to facilitate import into chloroplasts

Early stages in the biogenesis of eukaryotic β‐barrel proteins

Toc75‐V/OEP80 is processed during translocation into chloroplasts, and the membrane‐embedded form exposes its POTRA domain to the intermembrane space

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