NEW EMBO MEMBERS' REVIEW: Ion channels in the outer membranes of chloroplasts and mitochondria: open doors or regulated gates?

Bölter, Bettina; Soll, Jürgen

doi:10.1093/emboj/20.5.935

Cited by 75 publications

(67 citation statements)

References 65 publications

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“…From this indication, it is likely that acquisition of other soluble metal nutrients requires selective channels in bacteria. Similarly, mitochondria and chloroplasts are metal-rich organelles and contain numerous β-barrel outer membrane proteins, most of whose functions are not known (1). Similarity searches did not find obvious MnoP homologs, but further studies into understanding the basis of selectivity may yield new criteria on which to base a more refined search.…”

Section: Discussionmentioning

confidence: 99%

“…Inner membrane permeability is highly selective because of transporters with high specificity for ligands. Conversely, the outer membrane is generally assumed to be much less discriminating toward small hydrophilic solutes because of channels with no or broad substrate specificity that permit diffusion from the environment into the intermembrane space (1)(2)(3)(4)(5)(6). These channels are transmembrane proteins composed of amphipathic β-strands that form a β-barrel pore that allows solute translocation across the outer membrane.…”

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confidence: 99%

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Bacterial outer membrane channel for divalent metal ion acquisition

Hohle

Franck

Stacey

et al. 2011

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

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The prevailing model of bacterial membrane function predicts that the outer membrane is permeable to most small solutes because of pores with limited selectivity based primarily on size. Here, we identified mnoP in the Gram-negative bacterium Bradyrhizobium japonicum as a gene coregulated with the inner membrane Mn 2+ transporter gene mntH. MnoP is an outer membrane protein expressed specifically under manganese limitation. MnoP acts as a channel to facilitate the tranlocation of Mn 2+ , but not Co 2+ or Cu 2+ , into reconstituted proteoliposomes. An mnoP mutant is defective in high-affinity Mn 2+ transport into cells and has a severe growth phenotype under manganese limitation. We suggest that the outer membrane is a barrier to divalent metal ions that requires a selective channel to meet the nutritional needs of the cell.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Bacterial outer membrane channel for divalent metal ion acquisition

Hohle

Franck

Stacey

et al. 2011

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

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“…The outer envelope of plastids contains multiple solute channels whose substrate specificity has not been fully defined (36). Many of these channel proteins are abundant and prominent constituents of the outer membrane.…”

Section: Discussionmentioning

confidence: 99%

Chloroplast biogenesis: The use of mutants to study the etioplast–chloroplast transition

Philippar

Geis

Ilkavets

et al. 2007

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

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In angiosperm plants, the etioplast-chloroplast transition is lightdependent. A key factor in this process is the protochlorophyllide oxidoreductase A (PORA), which catalyzes the light-induced reduction of protochlorophyllide to chlorophyllide. The import pathway of the precursor protein prePORA into chloroplasts was analyzed in vivo and in vitro by using homozygous loss-of-function mutants in genes coding for chlorophyllide a oxygenase (CAO) or for members of the outer-envelope solute-channel protein family of 16 kDa (OEP16), both of which have been implied to be key factors for the import of prePORA. Our in vivo analyses show that cao or oep16 mutants contain a normally structured prolamellar body that contains the protochlorophyllide holochrome. Furthermore, etioplasts from cao and oep16 mutants contain PORA protein as found by mass spectrometry. Our data demonstrate that both CAO and OEP16 are dispensable for chloroplast biogenesis and play no central role in the import of prePORA in vivo and in vitro as further indicated by protein import studies.chlorophyllide a oxygenase ͉ chloroplast outer-envelope solute channel ͉ protein import ͉ protochlorophyllide oxidoreductase

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“…However, the protein composition of outer membranes is much simpler than that of inner membrane. The lipid to protein ratio of outer membrane is about 3 times higher than that of inner membrane and the inner envelope membrane, which contains various metabolite translocators, is the main permeability barrier for solutes, although there is growing evidence suggesting that the outer envelope may contain regulated ion channels (Cline et al, 1981;Block et al, 1983;Douce and Joyard, 1990;Pohlmeyer et al, 1998;Flugge, 2000;Bolter and Soll, 2001). Thus, we consider it likely that AtPEM candidates represent the majority of integral plastid envelope proteins.…”

Section: Plastid Envelope Membrane Protein Candidatesmentioning

confidence: 99%

The Predicted Candidates of Arabidopsis Plastid Inner Envelope Membrane Proteins and Their Expression Profiles,

Koo

Ohlrogge

2002

Plant Physiology

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Plastid envelope proteins from the Arabidopsis nuclear genome were predicted using computational methods. Selection criteria were: first, to find proteins with NH 2 -terminal plastid-targeting peptides from all annotated open reading frames from Arabidopsis; second, to search for proteins with membrane-spanning domains among the predicted plastidial-targeted proteins; and third, to subtract known thylakoid membrane proteins. Five hundred forty-one proteins were selected as potential candidates of the Arabidopsis plastid inner envelope membrane proteins (AtPEM candidates). Only 34% (183) of the AtPEM candidates could be assigned to putative functions based on sequence similarity to proteins of known function (compared with the 69% function assignment of the total predicted proteins in the genome). Of the 183 candidates with assigned functions, 40% were classified in the category of "transport facilitation," indicating that this collection is highly enriched in membrane transporters. Information on the predicted proteins, tissue expression data from expressed sequence tags and microarrays, and publicly available T-DNA insertion lines were collected. The data set complements proteomic-based efforts in the increased detection of integral membrane proteins, low-abundance proteins, or those not expressed in tissues selected for proteomic analysis. Digital northern analysis of expressed sequence tags suggested that the transcript levels of most AtPEM candidates were relatively constant among different tissues in contrast to stroma and the thylakoid proteins. However, both digital northern and microarray analyses identified a number of AtPEM candidates with tissue-specific expression patterns.Plastids exist in a wide range of differential forms, including proplastids, chloroplasts, etioplasts, amyloplasts, leucoplasts, and chromoplasts, depending on the developmental stage and function of the plant cells in which they reside. To a large extent, the types of plastids that are carried by cells determine the metabolic function and products of the particular plant tissue (Kirk and Tilney-Bassett, 1978).One constant feature among the various types of plastids is the double membrane envelope structure that surrounds the organelle. The envelope, especially the inner envelope, effectively separates plastid metabolism from that of the cytosol. At the same time, almost all carbon and a major flux of other metabolites, various polypeptides, and signals must move through the envelope to coordinate and integrate metabolism with the entire cell. Plastid envelopes contain protein transport machinery (Schnell, 1995;Cline and Henry, 1996;Heins et al., 1998), and are a major site for membrane biogenesis. Metabolite transporters from chloroplast and/or nongreen plastids accommodate the requirements of the different photosynthetic or heterotrophic tissues (Kammerer et al., 1998;Neuhaus and Emes, 2000). Membrane constituents (glycerolipids, pigments, and prenylquinones) are synthesized on the envelope membrane as well as the porphyrin ring ...

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NEW EMBO MEMBERS' REVIEW: Ion channels in the outer membranes of chloroplasts and mitochondria: open doors or regulated gates?

Cited by 75 publications

References 65 publications

Bacterial outer membrane channel for divalent metal ion acquisition

Bacterial outer membrane channel for divalent metal ion acquisition

Chloroplast biogenesis: The use of mutants to study the etioplast–chloroplast transition

The Predicted Candidates of Arabidopsis Plastid Inner Envelope Membrane Proteins and Their Expression Profiles,

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