Secretion of Bacterial Lipoproteins: Through the Cytoplasmic Membrane, the Periplasm and Beyond

Zückert, Wolfram R.

doi:10.1016/j.bbamcr.2014.04.022

Cited by 184 publications

(197 citation statements)

References 135 publications

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“…It is possible that the differences between the E. coli and P. aeruginosa Lol systems are significant enough that the pyridineimidazoles are not active against the P. aeruginosa LolCDE complex. Interestingly, homologs of the Lol proteins in spirochetes such as Borrelia burgdorferi have been described, but their susceptibilities to compounds 1 and 2 are not known (5).…”

Section: Discussionmentioning

confidence: 99%

“…LolA then transfers the lipoprotein to LolB, the outer membrane lipoprotein receptor, which incorporates these lipoproteins into the inner leaflet of the outer membrane (1,4). This is in contrast to Grampositive bacteria, which have a single membrane bilayer; therefore, localization of lipoproteins to the cell surface requires only export through the cytoplasmic membrane and acylation (5).…”

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confidence: 99%

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Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

et al. 2015

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cIn Gram-negative bacteria, lipoproteins are transported to the outer membrane by the Lol system. In this process, lipoproteins are released from the inner membrane by the ABC transporter LolCDE and passed to LolA, a diffusible periplasmic molecular chaperone. Lipoproteins are then transferred to the outer membrane receptor protein, LolB, for insertion in the outer membrane. Here we describe the discovery and characterization of novel pyridineimidazole compounds that inhibit this process. Escherichia coli mutants resistant to the pyridineimidazoles show no cross-resistance to other classes of antibiotics and map to either the LolC or LolE protein of the LolCDE transporter complex. The pyridineimidazoles were shown to inhibit the LolA-dependent release of the lipoprotein Lpp from E. coli spheroplasts. These results combined with bacterial cytological profiling are consistent with LolCDE-mediated disruption of lipoprotein targeting to the outer membrane as the mode of action of these pyridineimidazoles. The pyridineimidazoles are the first reported inhibitors of the LolCDE complex, a target which has never been exploited for therapeutic intervention. These compounds open the door to further interrogation of the outer membrane lipoprotein transport pathway as a target for antimicrobial therapy.T he most distinguishing feature of Gram-negative bacteria is their cell envelope, which is comprised of both an inner and an outer membrane bilayer. The outer membrane has a unique composition of lipoproteins, ␤-barrel proteins, lipopolysaccharides, and phospholipids. Lipoproteins, membrane proteins that are covalently modified with lipids, are involved in a variety of integral cellular functions, such as the synthesis and maintenance of the cell surface and the transport of substrates (reviewed in reference 1). Lipoproteins are synthesized as precursors in the cytoplasm. Upon transit across the inner membrane by either the Sec or Tat machinery, the export signal peptide is cleaved, and attached to its amino terminus is a lipid moiety. This lipid serves as a membrane anchor for the lipoprotein. Some lipoproteins remain in the outer leaflet of the inner membrane, while others must cross the hydrophilic periplasmic space to the outer membrane. This sorting of lipoproteins to the outer membrane is achieved by the Lol system, which consists of five proteins (Fig. 1) (reviewed in reference 1). In this process, lipoproteins destined for the outer membrane are released from the inner membrane by the LolCDE complex, an inner membrane ABC transporter. LolCDE transfers the lipoproteins to LolA, a diffusible periplasmic chaperone (2, 3). LolA then transfers the lipoprotein to LolB, the outer membrane lipoprotein receptor, which incorporates these lipoproteins into the inner leaflet of the outer membrane (1, 4). This is in contrast to Grampositive bacteria, which have a single membrane bilayer; therefore, localization of lipoproteins to the cell surface requires only export through the cytoplasmic membrane and acylation (5).Infections c...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

et al. 2015

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“…pTA963 is an overexpression vector derived from pBluescript II with the H. volcanii pHV2 replication origin in addition to both pyrE2 (encoding the product with accession number WP_004044590.1) and hdrB (encoding the product with accession number WP_004044748.1) markers. The plasmid also contains a 6ϫHis tag at the multiple-cloning site (MCS) by the insertion of a 26-bp fragment of a (CAC) 6 tract at the NdeI and PciI site (24).…”

Section: Methodsmentioning

confidence: 99%

“…Anchoring mechanisms involving either N-or C-terminal transmembrane segments have been well characterized in bacteria and archaea (1,(36)(37)(38). However, while anchoring mechanisms involving N-terminal covalently attached lipids have been studied in detail in bacteria (6,8) and archaeal proteins requiring the invariant lipobox cysteine for proper surface attachment have been identified (30), this is the first report to present evidence consistent with protein anchoring of secreted prokaryotic proteins that is mediated through the covalent attachment of a cell membrane lipid to the C terminus. Our findings provide a sound foundation for future biochemical and molecular biological studies that will allow us to fully understand the mechanisms underpinning the ArtA-dependent processing and lipidation of the C terminus of the SLG.…”

Section: Figmentioning

confidence: 99%

“…However, as cell membranes became densely packed with protein complexes, protein-anchoring mechanisms that allowed more economic use of membrane surface area emerged (5). One such mechanism anchors proteins through covalent attachment of their N-terminal cysteine to the lipid bilayer (6)(7)(8). In many Gram-positive bacteria, a subset of proteins are processed and anchored to the cell wall via the carboxy terminus (C terminus) by an enzyme known as sortase, a transpeptidase that recognizes a conserved tripartite structure at the C terminus consisting of a signature motif, a TM alpha-helical domain, and a cluster of basic residues (9).…”

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Permuting the PGF Signature Motif Blocks both Archaeosortase-Dependent C-Terminal Cleavage and Prenyl Lipid Attachment for the Haloferax volcanii S-Layer Glycoprotein

et al. 2016

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For years, the S-layer glycoprotein (SLG), the sole component of many archaeal cell walls, was thought to be anchored to the cell surface by a C-terminal transmembrane segment. Recently, however, we demonstrated that the Haloferax volcanii SLG C terminus is removed by an archaeosortase (ArtA), a novel peptidase. SLG, which was previously shown to be lipid modified, contains a C-terminal tripartite structure, including a highly conserved proline-glycine-phenylalanine (PGF) motif. Here, we demonstrate that ArtA does not process an SLG variant where the PGF motif is replaced with a PFG motif (slg G796F,F797G ). Furthermore, using radiolabeling, we show that SLG lipid modification requires the PGF motif and is ArtA dependent, lending confirmation to the use of a novel C-terminal lipid-mediated protein-anchoring mechanism by prokaryotes. Similar to the case for the ⌬artA strain, the growth, cellular morphology, and cell wall of the slg G796F,F797G strain, in which modifications of additional H. volcanii ArtA substrates should not be altered, are adversely affected, demonstrating the importance of these posttranslational SLG modifications. Our data suggest that ArtA is either directly or indirectly involved in a novel proteolysis-coupled, covalent lipid-mediated anchoring mechanism. Given that archaeosortase homologs are encoded by a broad range of prokaryotes, it is likely that this anchoring mechanism is widely conserved. IMPORTANCEProkaryotic proteins bound to cell surfaces through intercalation, covalent attachment, or protein-protein interactions play critical roles in essential cellular processes. Unfortunately, the molecular mechanisms that anchor proteins to archaeal cell surfaces remain poorly characterized. Here, using the archaeon H. volcanii as a model system, we report the first in vivo studies of a novel protein-anchoring pathway involving lipid modification of a peptidase-processed C terminus. Our findings not only yield important insights into poorly understood aspects of archaeal biology but also have important implications for key bacterial species, including those of the human microbiome. Additionally, insights may facilitate industrial applications, given that photosynthetic cyanobacteria encode uncharacterized homologs of this evolutionarily conserved enzyme, or may spur development of unique drug delivery systems.A variety of protein complexes decorate cell surfaces, where they support cell stability and facilitate interactions between the cell and the extracellular environment (1-3). Determining the mechanisms that allow these proteins to remain associated with the cell envelope is critical for developing a comprehensive understanding of the biosynthesis of cell surface structures. Protein anchoring to the cell membrane was likely first accomplished by means of transmembrane (TM) segments (4). However, as cell membranes became densely packed with protein complexes, protein-anchoring mechanisms that allowed more economic use of membrane surface area emerged (5). One such mechanism anchors...

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Mycobacterium tuberculosis lipoproteins in virulence and immunity – fighting with a double‐edged sword

Becker

Sander

2016

FEBS Letters

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Bacterial lipoproteins are secreted membrane‐anchored proteins characterized by a lipobox motif. This lipobox motif directs post‐translational modifications at the conserved cysteine through the consecutive action of three enzymes: Lgt, LspA and Lnt, which results in di‐ or triacylated forms. Lipoproteins are abundant in all bacteria including Mycobacterium tuberculosis and often involved in virulence and immunoregulatory processes. On the one hand, disruption of the biosynthesis pathway of lipoproteins leads to attenuation of M. tuberculosis in vivo, and mycobacteria deficient for certain lipoproteins have been assessed as attenuated live vaccine candidates. On the other hand, several mycobacterial lipoproteins form immunodominant antigens which promote an immune response. Some of these have been explored in DNA or subunit vaccination approaches against tuberculosis. The immune recognition of specific lipoproteins, however, might also benefit long‐term survival of M. tuberculosis through immune modulation, while others induce protective responses. Exploiting lipoproteins as vaccines is thus a complex matter which requires deliberative investigation. The dual role of lipoproteins in the immunity to and pathogenicity of mycobacteria is discussed here.

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Secretion of Bacterial Lipoproteins: Through the Cytoplasmic Membrane, the Periplasm and Beyond

Cited by 184 publications

References 135 publications

Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

Permuting the PGF Signature Motif Blocks both Archaeosortase-Dependent C-Terminal Cleavage and Prenyl Lipid Attachment for the Haloferax volcanii S-Layer Glycoprotein

Mycobacterium tuberculosis lipoproteins in virulence and immunity – fighting with a double‐edged sword

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