Genetic analysis of the membrane insertion and topology of MalF, a cytoplasmic membrane protein of Escherichia coli

Froshauer, S; Gn, Green; Boyd, Dana; McGovern, Karen; Beckwith, Jon

doi:10.1016/0022-2836(88)90539-6

Cited by 173 publications

(118 citation statements)

References 30 publications

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“…The folding patterns of MalF and MalG were studied using the alkaline phosphatase fusion method [21,22]. They were found to cross the membrane 8 and 6 times, respectively, a finding consistent with the notion that they form the transmembrane channel.…”

Section: The Membrane-associated Transportersupporting

confidence: 56%

Maltose transport system of Escherichia coli: An ABC‐type transporter

Nikaido

1994

FEBS Letters

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The maltose transport system of E. coli is composed of a periplasmic maltose-binding protein (MBP), the presumed transmembrane channel made up of MalF and MalG proteins, and two copies of the ATPase subunit, MalK. The membrane-associated transporter complex was purified in a functional form both from the wild-type strain and from mutants that do not require MBP for transport, and was reconstituted into proteoliposomes. A major function of MBP is to send a transmembrane signal, in the presence of ligands, to the ATPase subunits on the inner side of the membrane. In addition, MBP performs a special function in the translocation of the larger ligands, maltodextrins, perhaps by aligning them for entry into the channel.

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Section: The Membrane-associated Transportersupporting

confidence: 56%

Maltose transport system of Escherichia coli: An ABC‐type transporter

Nikaido

1994

FEBS Letters

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“…Cells were lysed as described (25). Alkaline phosphatase and OmpA proteins were immunoprecipitated as described (32). A 10% SDS͞PAGE gel was used to separate immunoprecipitated proteins.…”

Section: Methodsmentioning

confidence: 99%

The reductive enzyme thioredoxin 1 acts as an oxidant when it is exported to the Escherichia coli periplasm

Debarbieux

Beckwith

1998

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

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Thioredoxin 1 is a major thiol-disulfide oxidoreductase in the cytoplasm of Escherichia coli. One of its functions is presumed to be the reduction of the disulfide bond in the active site of the essential enzyme ribonucleotide reductase. Thioredoxin 1 is kept in a reduced state by thioredoxin reductase. In a thioredoxin reductase null mutant however, most of thioredoxin 1 is in the oxidized form; recent reports have suggested that this oxidized form might promote disulfide bond formation in vivo. In the Escherichia coli periplasm, the protein disulfide isomerase DsbC is maintained in the reduced and active state by the membrane protein DsbD. In a dsbD null mutant, DsbC accumulates in the oxidized form. This oxidized form is then able to promote disulfide bond formation. In both these cases, the inversion of the function of these thiol oxidoreductases appears to be due to an altered redox balance of the environment in which they find themselves. Here, we show that thioredoxin 1 attached to the alkaline phosphatase signal sequence can be exported into the E. coli periplasm. In this new environment for thioredoxin 1, we show that thioredoxin 1 can promote disulfide bond formation and, therefore, partially complement a dsbA strain defective for disulfide bond formation. Thus, we provide evidence that by changing the location of thioredoxin 1 from cytoplasm to periplasm, we change its function from a reductant to an oxidant. We conclude that the in vivo redox function of thioredoxin 1 depends on the redox environment in which it is localized.

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“…We have determined that HOP-1 has these essential features of presenilin topology by using the LacZ hybrid protein approach that we used to deduce the topology of SEL-12 presenilin (9). If LacZ is fused at different points in a membrane protein, its location in the cytosol or in an extracytosolic compartment, and hence the topology of the membrane protein, can be deduced by its activity, because ␤-galactosidase is active within the cytosol but not in the extracytosolic compartment (20,21).…”

Section: Resultsmentioning

confidence: 99%

HOP-1, a Caenorhabditis elegans presenilin, appears to be functionally redundant with SEL-12 presenilin and to facilitate LIN-12 and GLP-1 signaling

Greenwald

1997

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

155

127

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Mutant presenilins have been found to cause Alzheimer disease. Here, we describe the identification and characterization of HOP-1, a Caenorhabditis elegans presenilin that displays much more lower sequence identity with human presenilins than does the other C. elegans presenilin, SEL-12. Despite considerable divergence, HOP-1 appears to be a bona fide presenilin, because HOP-1 can rescue the egg-laying defect caused by mutations in sel-12 when hop-1 is expressed under the control of sel-12 regulatory sequences. HOP-1 also has the essential topological characteristics of the other presenilins. Reducing hop-1 activity in a sel-12 mutant background causes synthetic lethality and terminal phenotypes associated with reducing the function of the C. elegans lin-12 and glp-1 genes. These observations suggest that hop-1 is functionally redundant with sel-12 and underscore the intimate connection between presenilin activity and LIN-12͞ Notch activity inferred from genetic studies in C. elegans and mammals.Genetic linkage studies have identified a number of loci associated with familial Alzheimer disease (1). Two of these loci encode related multipass transmembrane proteins, presenilins 1 and 2 (PS1 and PS2). Mutations in the genes encoding PS1 and PS2 loci are dominant and fully penetrant for early onset Alzheimer disease (2-4). The presenilins are ubiquitously expressed (3, 4) and found in conjunction with intracellular membranes (5). However, the normal role of presenilins, and the mechanism by which mutant presenilins cause Alzheimer disease, are not known.Genetic studies in simple organisms offer a powerful approach to understanding the normal role of presenilins. The Caenorhabditis elegans sel-12 gene encodes a protein that displays about 50% amino acid sequence identity to PS1 and PS2 (6). Genetic analysis established that reducing or eliminating sel-12 activity causes an egg-laying defective (Egl) phenotype, and that sel-12 activity facilitates the activity of LIN-12 and GLP-1, two receptors of the LIN-12͞Notch family (6). SEL-12 appears to be a bona fide presenilin, because human PS1 and PS2 can rescue the Egl phenotype of a sel-12 mutant (7). Furthermore, the membrane topology of SEL-12 and PS1 appears to be similar (8-10). In addition to the functional and structural similarities, expression studies indicate that SEL-12 and human presenilins are expressed throughout development in many different cell types (3, 4, 7).We have identified another candidate C. elegans presenilin based on predicted amino acid sequence by searching the genomic sequence database (11,12). Here, we show that this gene, which we have named hop-1 (hop ϭ homolog of presenilin), encodes a functional presenilin, by demonstrating that HOP-1 can rescue the egg-laying defect of a sel-12 mutant. We also show that HOP-1 has characteristic features of presenilin membrane topology. Finally, we show that reducing hop-1 activity in a sel-12 mutant background results in novel phenotypes, suggesting that hop-1 and sel-12 are functionally redundant.

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Genetic analysis of the membrane insertion and topology of MalF, a cytoplasmic membrane protein of Escherichia coli

Cited by 173 publications

References 30 publications

Maltose transport system of Escherichia coli: An ABC‐type transporter

Maltose transport system of Escherichia coli: An ABC‐type transporter

The reductive enzyme thioredoxin 1 acts as an oxidant when it is exported to the Escherichia coli periplasm

HOP-1, a Caenorhabditis elegans presenilin, appears to be functionally redundant with SEL-12 presenilin and to facilitate LIN-12 and GLP-1 signaling

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