In Vivo Analyses of the Roles of Essential Omp85-Related Proteins in the Chloroplast Outer Envelope Membrane

Huang, Weihua; Ling, Qihua; Bédard, Jocelyn; Lilley, Kathryn S.; Jarvis, Paul

doi:10.1104/pp.111.181891

Cited by 52 publications

(78 citation statements)

References 57 publications

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“…23,24 As atToc75-III is a prominent β-barrel protein in the outer envelope, this model can readily explain the similar phenotypes of the atToc75-III↓ and AtOEP80↓ RNAi lines. 7 Moreover, atToc75-III protein levels are significantly reduced in AtOEP80↓ lines, more so than other outer membrane proteins, 7 providing more direct evidence in support of the hypothesis. However, one potentially conflicting point is that the AtOEP80↓ plants display more pronounced chlorosis in first true leaves than in cotyledons, while atToc75-III↓ plants have a uniform phenotype.…”

Section: Possible Functions Of the Oep80 Proteinmentioning

confidence: 50%

“…7 Remarkably, the atToc75-III↓ and AtOEP80↓ knockdown phenotypes were very similar, as judged by a variety of criteria: both are characterized by smaller leaves, chlorophyll deficiency, shorter roots and hypocotyls, under-developed plastids of different types, and altered levels of chloroplast proteins, although the atToc75-III↓ defects were more severe in each case. This suggests two possibilities: (1) that Toc75 and OEP80 act redundantly, with Toc75 being the major functional form; or (2) that the roles of Toc75 and OEP80 are distinct, but nonetheless closely related.…”

Section: Possible Functions Of the Oep80 Proteinmentioning

confidence: 96%

“…5,6 The lethality of the knockout mutations limits their use in relation to functional in vivo analyses, and so in a recent study inducible RNA interference (RNAi) was used to knockdown expression of the genes during postembryonic growth. 7 This revealed the importance of both genes during later stages of development, with loss of function characterized by visible chlorosis and retarded growth in both photosynthetic and non-photosynthetic tissues. The work led to the conclusion that neither protein exhibits specificity for photosynthetic or non-photosynthetic growth, which distinguishes them from receptor components of the TOC complex.…”

Section: Chloroplasts Protein Import and Omp85-related Proteinsmentioning

confidence: 99%

“…2 In fact, uptake assays using chloroplasts isolated from Toc75 knockdown (atToc75-III↓) plants revealed defective import of both photosynthetic and non-photosynthetic precursor proteins. 7 …”

Section: Chloroplasts Protein Import and Omp85-related Proteinsmentioning

confidence: 99%

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Neofunctionalization within the Omp85 protein superfamily during chloroplast evolution

Töpel

Ling

Jarvis

2012

Plant Signaling & Behavior

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The Toc75 and OEP80 proteins reside in the chloroplast outer envelope membrane. Both are members of the Omp85 superfamily of b-barrel proteins, and both are essential in Arabidopsis plants with important roles throughout development. Toc75 forms the translocation channel of the TOC complex, which is responsible for importing nucleus-encoded proteins into chloroplasts, while the function of OEP80 remains uncertain. Deficiency of Toc75 in plants that have artificially reduced OEP80 levels suggests that the latter may be involved in the biogenesis of b-barrel proteins, in similar fashion to Omp85-related proteins in other systems. To elucidate the evolutionary relationship between the two proteins, we conducted a phylogenetic analysis using 48 sequences from diverse species. This indicated that Toc75 and OEP80 belong to sister groups in the Omp85 superfamily, and originate from a gene duplication in an ancient eukaryotic organism . 1.2 billion years ago. Our analysis also supports the notion that the Toc75 family has undergone a phase of neofunctionalization to accommodate the organelle's newly acquired need to import proteins. Chloroplasts, Protein Import, and Omp85-Related ProteinsChloroplasts evolved through endosymbiosis from an ancient relative of extant cyanobacteria approximately 1.5 billion years ago.1 Ensuing organellar genome reduction and the transfer of genetic material to the nucleus together led to the need for modern chloroplasts to import . 90% of the 3,000 or so different proteins that are required for organellar functions. This import process is mediated by multiprotein complexes in the double membrane surrounding each organelle, termed TOC and TIC (translocon at the outer/inner envelope membrane of chloroplasts). 2The β-barrel protein Toc75 is a core component of the TOC complex and it forms the main translocation channel in the outer membrane. Furthermore, Toc75 is a member of a ubiquitous family of proteins that all possess a similar structure, which together are often referred to as the Omp85 (or BamA) superfamily.3,4 Other family members include Omp85, which mediates outer membrane protein biogenesis in Gram-negative bacteria, and Sam50/Tob55, which performs a similar role in mitochondria. Interestingly, in chloroplasts there is a second Omp85 family member called OEP80 (outer envelope protein of 80 kDa; or Toc75-V, the Roman numeral being a reference to the chromosomal location of the gene in Arabidopsis). The role of OEP80 is uncertain, although functional analogy with bacterial Omp85 and mitochondrial Sam50/Tob55 has been proposed.In Arabidopsis, the only full-length Toc75 and OEP80 genes (i.e., atTOC75-III and AtOEP80, respectively) are essential, with knockout mutants causing embryo abortion. 5,6 The lethality of the knockout mutations limits their use in relation to functional in vivo analyses, and so in a recent study inducible RNA interference (RNAi) was used to knockdown expression of the genes during postembryonic growth.7 This revealed the importance of both genes during later stag...

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Section: Possible Functions Of the Oep80 Proteinmentioning

confidence: 50%

Section: Possible Functions Of the Oep80 Proteinmentioning

confidence: 96%

Section: Chloroplasts Protein Import and Omp85-related Proteinsmentioning

confidence: 99%

Section: Chloroplasts Protein Import and Omp85-related Proteinsmentioning

confidence: 99%

See 2 more Smart Citations

Neofunctionalization within the Omp85 protein superfamily during chloroplast evolution

Töpel

Ling

Jarvis

2012

Plant Signaling & Behavior

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“…These proteins are assembled into their native membranes by conserved protein complexes, which contain a β-barrel protein of the outer membrane protein 85 (Omp85) family and some number of accessory proteins (1)(2)(3)(4)(5)(6). β-barrel assembly is an essential process and, as such, is an attractive target for the development of new antibiotics that could kill Gram-negative pathogens.…”

mentioning

confidence: 99%

Inhibition of the β-barrel assembly machine by a peptide that binds BamD

Hagan

Wzorek

Kahne

2015

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

112

145

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The protein complex that assembles integral membrane β-barrel proteins in the outer membranes of Gram-negative bacteria is an attractive target in the development of new antibiotics. This complex, the β-barrel assembly machine (Bam), contains two essential proteins, BamA and BamD. We have identified a peptide that inhibits the assembly of β-barrel proteins in vitro by characterizing the interaction of BamD with an unfolded substrate protein. This peptide is a fragment of the substrate protein and contains a conserved amino acid sequence. We have demonstrated that mutations of this sequence in the full-length substrate protein impair the protein's assembly, implying that BamD's interaction with this sequence is an important part of the assembly mechanism. Finally, we have found that in vivo expression of a peptide containing this sequence causes growth defects and sensitizes Escherichia coli to antibiotics to which they are normally resistant. Therefore, inhibiting the binding of substrates to BamD is a viable strategy for developing new antibiotics directed against Gram-negative bacteria.β-barrel | outer membrane | protein folding | Bam complex | inhibition

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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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In Vivo Analyses of the Roles of Essential Omp85-Related Proteins in the Chloroplast Outer Envelope Membrane

Cited by 52 publications

References 57 publications

Neofunctionalization within the Omp85 protein superfamily during chloroplast evolution

Neofunctionalization within the Omp85 protein superfamily during chloroplast evolution

Inhibition of the β-barrel assembly machine by a peptide that binds BamD

Early stages in the biogenesis of eukaryotic β‐barrel proteins

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