Lipoproteins of Gram-Positive Bacteria: Key Players in the Immune Response and Virulence

Nguyen, Minh Thu; Götz, Friedrich

doi:10.1128/mmbr.00028-16

Cited by 154 publications

(183 citation statements)

References 129 publications

(122 reference statements)

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“…In contrast to the essential role of Lnt in E. coli, lipoproteins are nonessential in many firmicutes (3,5), and there are no known phenotypes attributable to the N-terminal acylation state that could be used for direct selection in native hosts. We hypothesized that as long as lipoproteins were N-acylated, whether in triacylated or lyso form, they would be compatible substrates for the E. coli localization of lipoproteins (Lol) export machinery, since triacyl and lyso-form lipoproteins both share an ␣-amino-linked acyl chain (4).…”

Section: Resultsmentioning

confidence: 99%

“…However, there are no apparent lnt sequence orthologs in firmicute genomes, nor are there any known examples of enzymecatalyzed lipoprotein intramolecular transacylation (5). The general function of lipoprotein aminoacylation among firmicutes also remains to be seen.…”

mentioning

confidence: 99%

“…ipoproteins are bacterial cell membrane components common throughout Gramnegative and Gram-positive bacteria, constituting 2 to 5% of all cellular proteins (1)(2)(3)(4)(5). Lipoproteins invariably contain a signature acylated N-terminal cysteine residue that tethers an otherwise soluble globular protein domain to the membrane surface.…”

mentioning

confidence: 99%

“…In Escherichia coli and other Gram-negative bacteria, biosynthesis is completed by an apolipoprotein N-acyltransferase (Lnt), which transfers a fatty acid from a membrane phospholipid to form an amide linkage (10). While both Lgt and Lsp are highly conserved across genera, lnt sequence orthologs are confined to Gram-negative bacteria and mycobacteria, which also make triacylated lipoproteins (5,11). However, lipoprotein N-terminal modification in other Gram-positive bacteria still occurs and, in low-GC firmicutes in particular, is more complex and varied than previously appreciated (2).…”

mentioning

confidence: 99%

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Identification of the Lyso-Form N -Acyl Intramolecular Transferase in Low-GC Firmicutes

Armbruster

Meredith

2017

J Bacteriol

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Bacterial lipoproteins are embedded in the cell membrane of both Gram-positive and Gram-negative bacteria, where they serve numerous functions central to cell envelope physiology. Lipoproteins are tethered to the membrane by an N-acyl-S-(mono/di)-acyl-glyceryl-cysteine anchor that is variously acylated depending on the genus. In several low-GC, Gram-positive firmicutes, a monoacyl-glycerylcysteine with an N-terminal fatty acid (known as the lyso form) has been reported, though how it is formed is unknown. Here, through an intergenic complementation rescue assay in Escherichia coli, we report the identification of a common orthologous transmembrane protein in both Enterococcus faecalis and Bacillus cereus that is capable of forming lyso-form lipoproteins. When deleted from the native host, lipoproteins remain diacylated with a free N terminus, as maturation to the N-acylated lyso form is abolished. Evidence is presented suggesting that the previously unknown gene product functions through a novel intramolecular transacylation mechanism, transferring a fatty acid from the diacylglycerol moiety to the ␣-amino group of the lipidated cysteine. As such, the discovered gene has been named lipoprotein intramolecular transacylase (lit), to differentiate it from the gene for the intermolecular N-acyltransferase (lnt) involved in triacyl lipoprotein biosynthesis in Gram-negative organisms.IMPORTANCE This study identifies a new enzyme, conserved among low-GC, Grampositive bacteria, that is involved in bacterial lipoprotein biosynthesis and synthesizes lyso-form lipoproteins. Its discovery is an essential first step in determining the physiological role of N-terminal lipoprotein acylation in Gram-positive bacteria and how these modifications impact bacterial cell envelope function.KEYWORDS firmicutes, acyl transferase, lipoproteins L ipoproteins are bacterial cell membrane components common throughout Gramnegative and Gram-positive bacteria, constituting 2 to 5% of all cellular proteins (1-5). Lipoproteins invariably contain a signature acylated N-terminal cysteine residue that tethers an otherwise soluble globular protein domain to the membrane surface. Positioned at the membrane-environment interface, lipoproteins play critical roles in ion and nutrient capture, solute transport, cell adhesion, and assembly of protein complexes and as protein-folding chaperones.All lipoproteins are initially translated as precursors containing an N-terminal signal peptide harboring a conserved amino acid lipobox motif sequence preceding an invariant cysteine residue (6, 7). Once transported to the outer face of the membrane, prolipoprotein diacylglycerol transferase (Lgt) attaches a diacylglycerol residue from a phospholipid donor through a thioether bond (8). Signal peptidase II (Lsp) then cleaves the leader peptide immediately upstream from the cysteine to liberate the ␣-amino group (9). In Escherichia coli and other Gram-negative bacteria, biosynthesis is completed by an apolipoprotein N-acyltransferase (Lnt), which transfers a...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Identification of the Lyso-Form N -Acyl Intramolecular Transferase in Low-GC Firmicutes

Armbruster

Meredith

2017

J Bacteriol

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“…38 Since LTA are also amphiphile, complete separation of lipoproteins and LTA is impossible in most bacteria. However, the lipoproteins in Gram-positive bacteria can be depleted by deletion of lgt in the genome.…”

Section: Discussionmentioning

confidence: 99%

TLR2-stimulating contaminants in glycoconjugate fractions prepared from Bacteroides fragilis

et al. 2017

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Bacteroides fragilis is a member of the normal intestinal flora and is involved in host immunostimulation via TLR2. On the bacterial cell surface, glycoconjugates, such as LPS and capsular polysaccharide A (PSA), have been reported to participate in host immunostimulation via TLR2. Previously, we identified a TLR2-stimulating lipoprotein in B. fragilis cells. In this study, we demonstrated that TLR2-stimulating principal molecules in glycoconjugate fractions prepared from B. fragilis are contaminating proteinous molecules, which may also be lipoproteins. The glycoconjugate fractions were prepared by phenol-hot water extraction of B. fragilis wild type and PSA-deficient strains, followed by hydrophobic interaction chromatography. TLR2-stimilating activities of the fractions were not affected by PSA deficiency. By in-gel TLR2-stimulation assay, molecules in high-molecular-mass area, where capsular polysaccharides were migrated, were found not to stimulate TLR2, but those in the range of 15-40 kDa were active. Further, proteinase K could digest the latter molecules and the TLR2-stimulating activities were migrated to the area of below 15 kDa. These results support that proteinous molecules, which are estimated to be lipoproteins, are responsible for almost all TLR2-stimulating activity in the glycoconjugate fractions prepared from B. fragilis.

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Demonstrating the immunostimulatory and cytokine‐augmentation effects of bacterial ghosts on natural killer cells and Caenorhabditis Elegans

Narayanan,

Baburajan,

Muhammad

et al. 2023

Biotech & Bioengineering

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The potential of bacteria‐based immunotherapy lies in its ability to inherently enhance immune responses. However, the “liveness” of bacteria poses risks of bacterial escape, nonspecific immuno‐stimulation, and ethical concerns, limiting their acceptability in immunotherapy. In this scenario, nonliving empty bacterial‐cell envelopes, named bacterial ghosts (BGs), have emerged as immuno‐stimulants with the potential to side‐step the limitations of live bacterial therapies. This study demonstrates the capability of BGs in modulating the functionality of NK‐92 cells and Caenorhabditis elegans (C. elegans), as well as perform as cytokine‐therapy adjuvants. BGs were obtained through a pH‐driven culture method, and were validated for their structural and chemical integrity via electron microscopy and spectroscopy. In NK‐92 cells, BGs have shown significant immuno‐stimulation by boosting the gene‐expression of perforin, granzyme‐B, Fas‐L, and interferon‐gamma by factors of 3.5‐, 1.5‐, 12.5‐, and 8.6‐folds, respectively. Combined BG and IL‐12 treatment yielded a notable 10.2‐fold increase in interferon‐gamma protein expression in 24 h. The BGs also significantly influenced the innate immune response in C. elegans through the upregulation of lysozyme genes viz., ilys‐3 (8.8‐fold) and lys‐2 (3.1‐fold). Our investigation into the impact of BGs on natural killer cells and C. elegans highlights its potential as a valid alternative approach for new‐age immunotherapy and cytokine augmentation.

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Lipoproteins of Gram-Positive Bacteria: Key Players in the Immune Response and Virulence

Cited by 154 publications

References 129 publications

Identification of the Lyso-Form N -Acyl Intramolecular Transferase in Low-GC Firmicutes

Identification of the Lyso-Form N -Acyl Intramolecular Transferase in Low-GC Firmicutes

TLR2-stimulating contaminants in glycoconjugate fractions prepared from Bacteroides fragilis

Demonstrating the immunostimulatory and cytokine‐augmentation effects of bacterial ghosts on natural killer cells and Caenorhabditis Elegans

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