Lipopolysaccharide Transport Research Articles

Mutations in genes lpxL1, bamA, and pmrB impair the susceptibility of cystic fibrosis strains of Pseudomonas aeruginosa to murepavadin.

Murepavadin is a peptidomimetic exhibiting specific inhibitory activity against Pseudomonas species. In the present study, its in vitro activity was assessed on 230 cystic fibrosis (CF) strains of Pseudomonas aeruginosa isolated from 12 French hospitals, in comparison with 12 other antipseudomonal antibiotics. Although murepavadin is still in preclinical stage of development, 9.1% (n = 21) of strains had a minimum inhibitory concentration (MIC) >4 mg/L, a level at least 128-fold higher than the modal MIC value of the whole collection (≤0.06 mg/L). Whole-genome sequencing of these 21 strains along with more susceptible isogenic counterparts coexisting in the same patients revealed diverse mutations in genes involved in the synthesis (lpxL1 and lpxL2) or transport of lipopolysaccharides (bamA, lptD, and msbA), or encoding histidine kinases of two-component systems (pmrB and cbrA). Allelic replacement experiments with wild-type reference strain PAO1 confirmed that alteration of genes lpxL1, bamA, and/or pmrB can decrease the murepavadin susceptibility from 8- to 32-fold. Furthermore, we found that specific amino acid substitutions in histidine kinase PmrB (G188D, Q105P, and D45E) reduce the susceptibility of P. aeruginosa to murepavadin, colistin, and tobramycin, three antibiotics used or intended to be used (murepavadin) in aerosols to treat colonized CF patients. Whether colistin or tobramycin may select mutants resistant to murepavadin or the opposite needs to be addressed by clinical studies.

Physiological and transcriptomic changes drive robust responses in Paenarthrobacter sp. AT5 to co-exposure of sulfamethoxazole and atrazine

Agricultural waterways are often contaminated with herbicide and antibiotic residues due to the widespread use of these chemicals in modern agriculture. The search for resistant bacterial strains that can adapt to and degrade these mixed contaminants is essential for effective in situ bioremediation. Herein, by integrating chemical and transcriptomic analyses, we shed light on mechanisms through which Paenarthrobacter sp. AT5, a well-known atrazine-degrading bacterial strain, can adapt to sulfamethoxazole (SMX) while degrading atrazine. When exposed to SMX and/or atrazine, strain AT5 increased the production of extracellular polymeric substances and reactive oxygen species, as well as the rate of activity of antioxidant enzymes. Atrazine and SMX, either alone or combined, increased the expression of genes involved in antioxidant responses, multidrug resistance, DNA repair, and membrane transport of lipopolysaccharides. Unlike atrazine alone, co-exposure with SMX reduced the expression of genes encoding enzymes involved in the lower part of the atrazine degradation pathway. Overall, these findings emphasize the complexity of bacterial adaptation to mixed herbicide and antibiotic residues and highlight the potential of strain AT5 in bioremediation efforts.

Murepavadin induces envelope stress response and enhances the killing efficacies of β-lactam antibiotics by impairing the outer membrane integrity of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that can cause a variety of acute and chronic infections. The bacterium is highly resistant to numerous antibiotics. Murepavadin is a peptidomimetic antibiotic that blocks the function of P. aeruginosa lipopolysaccharide (LPS) transport protein D (LptD), thus inhibiting the insertion of LPS into the outer membrane. In this study, we demonstrated that sublethal concentrations of murepavadin enhance the bacterial outer membrane permeability. Proteomic analyses revealed the alteration of protein composition in bacterial inner and outer membranes following murepavadin treatment. The antisigma factor MucA was upregulated by murepavadin. In addition, the expression of the sigma E factor gene algU and the alginate synthesis gene algD was induced by murepavadin. Deletion of the algU gene reduces bacterial survival following murepavadin treatment, indicating a role of the envelope stress response in bacterial tolerance. We further demonstrated that murepavadin enhances the bactericidal activities of β-lactam antibiotics by promoting drug influx across the outer membrane. In a mouse model of acute pneumonia, the murepavadin-ceftazidime/avibactam combination showed synergistic therapeutic effect against P. aeruginosa infection. In addition, the combination of murepavadin with ceftazidime/avibactam slowed down the resistance development. In conclusion, our results reveal the response mechanism of P. aeruginosa to murepavadin and provide a promising antibiotic combination for the treatment of P. aeruginosa infections.IMPORTANCEThe ever increasing resistance of bacteria to antibiotics poses a serious threat to global public health. Novel antibiotics and treatment strategies are urgently needed. Murepavadin is a novel antibiotic that blocks the assembly of lipopolysaccharide (LPS) into the Pseudomonas aeruginosa outer membrane by inhibiting LPS transport protein D (LptD). Here, we demonstrated that murepavadin impairs bacterial outer membrane integrity, which induces the envelope stress response. We further found that the impaired outer membrane integrity increases the influx of β-lactam antibiotics, resulting in enhanced bactericidal effects. In addition, the combination of murepavadin and a β-lactam/β-lactamase inhibitor mixture (ceftazidime/avibactam) slowed down the resistance development of P. aeruginosa. Overall, this study demonstrates the bacterial response to murepavadin and provides a new combination strategy for effective treatment.

Single-Cell Detection of Erwinia amylovora Using Bio-Functionalized SIS Sensor.

Herein, we developed a bio-functionalized solution-immersed silicon (SIS) sensor at the single-cell level to identify Erwinia amylovora (E. amylovora), a highly infectious bacterial pathogen responsible for fire blight, which is notorious for its rapid spread and destructive impact on apple and pear orchards. This method allows for ultra-sensitive measurements without pre-amplification or labeling compared to conventional methods. To detect a single cell of E. amylovora, we used Lipopolysaccharide Transporter E (LptE), which is involved in the assembly of lipopolysaccharide (LPS) at the surface of the outer membrane of E. amylovora, as a capture agent. We confirmed that LptE interacts with E. amylovora via LPS through in-house ELISA analysis, then used it to construct the sensor chip by immobilizing the capture molecule on the sensor surface modified with 3'-Aminopropyl triethoxysilane (APTES) and glutaraldehyde (GA). The LptE-based SIS sensor exhibited the sensitive and specific detection of the target bacterial cell in real time. The dose-response curve shows a linearity (R2 > 0.992) with wide dynamic ranges from 1 to 107 cells/mL for the target bacterial pathogen. The sensor showed the value change (dΨ) of approximately 0.008° for growing overlayer thickness induced from a single-cell E. amylovora, while no change in the control bacterial cell (Bacillus subtilis) was observed, or negligible change, if any. Furthermore, the bacterial sensor demonstrated a potential for the continuous detection of E. amylovora through simple surface regeneration, enabling its reusability. Taken together, our system has the potential to be applied in fields where early symptoms are not observed and where single-cell or ultra-sensitive detection is required, such as plant bacterial pathogen detection, foodborne pathogen monitoring and analysis, and pathogenic microbial diagnosis.

Conformational investigation of the asymmetric periplasmic domains of E. coli LptB2FGC using SDSL CW EPR spectroscopy.

The majority of pathogenic Gram-negative bacteria benefit from intrinsic antibiotic resistance, attributed primarily to the lipopolysaccharide (LPS) coating of the bacterial envelope. To effectively coat the bacterial cell envelope, LPS is transported from the inner membrane by the LPS transport (Lpt) system, which comprises seven distinct Lpt proteins, LptA-G, that form a stable protein bridge spanning the periplasm to connect the inner and outer membranes. The driving force of this process, LptB2FG, is an asymmetric ATP binding cassette (ABC) transporter with a novel architecture and function that ejects LPS from the inner membrane and facilitates transfer to the periplasmic bridge. Here, we utilize site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy to probe conformational differences between the periplasmic domains of LptF and LptG. We show that LptC solely interacts with the edge β-strand of LptF and does not directly interact with LptG. We also quantify the interaction of periplasmic LptC with LptF. Additionally, we show that LPS cannot enter the protein complex externally, supporting the unidirectional LPS transport model. Furthermore, we present our findings that the presence of LPS within the LptB2FGC binding cavity and the membrane reconstitution environment affect the structural orientation of the periplasmic domains of LptF and LptG, but overall are relatively fixed with respect to one another. This study will provide insight into the structural asymmetry associated with the newly defined type VI ABC transporter class.

Role of efflux pumps, their inhibitors, and regulators in colistin resistance.

Colistin is highly promising against multidrug-resistant and extensively drug-resistant bacteria clinically. Bacteria are resistant to colistin mainly through mcr and chromosome-mediated lipopolysaccharide (LPS) synthesis-related locus variation. However, the current understanding cannot fully explain the resistance mechanism in mcr-negative colistin-resistant strains. Significantly, the contribution of efflux pumps to colistin resistance remains to be clarified. This review aims to discuss the contribution of efflux pumps and their related transcriptional regulators to colistin resistance in various bacteria and the reversal effect of efflux pump inhibitors on colistin resistance. Previous studies suggested a complex regulatory relationship between the efflux pumps and their transcriptional regulators and LPS synthesis, transport, and modification. Carbonyl cyanide 3-chlorophenylhydrazone (CCCP), 1-(1-naphthylmethyl)-piperazine (NMP), and Phe-Arg-β-naphthylamide (PAβN) all achieved the reversal of colistin resistance, highlighting the role of efflux pumps in colistin resistance and their potential for adjuvant development. The contribution of the efflux pumps to colistin resistance might also be related to specific genetic backgrounds. They can participate in colistin tolerance and heterogeneous resistance to affect the treatment efficacy of colistin. These findings help understand the development of resistance in mcr-negative colistin-resistant strains.

Binding and transport of LPS occurs through the coordinated combination of an array of sites across the entire Escherichia coli LPS transport protein LptA.

The outer leaflet of the outer membrane (OM) of bacteria such as Escherichia coli, Pseudomonas aeruginosa, and other important pathogens is largely composed of lipopolysaccharide (LPS), which is essential to nearly all Gram-negative bacteria. LPS is transported to the outer leaflet of the OM through a yet unknown mechanism by seven proteins that comprise the LPS transport system. LptA, the only entirely periplasmic Lpt protein, bridges the periplasmic space between the IM LptB2 FGC and the OM LptDE complexes. LptA is postulated to protect the hydrophobic acyl chains of LPS as it crosses the hydrophilic periplasm, is essential to cell viability, and contains many conserved residues distributed across the protein. To identify which side chains are required for function of E. coli LptA in vivo, we performed a systematic, unbiased, high-throughput screen of the effect of 172 single alanine substitutions on cell viability utilizing an engineered BL21 derivative with a chromosomal knockout of the lptA gene. Remarkably, LptA is highly tolerant to amino acid substitution with alanine. Only four alanine mutants could not complement the chromosomal knockout; CD spectroscopy showed that these substitutions resulted in proteins with significantly altered secondary structure. In addition, 29 partial loss-of-function mutants were identified that led to OM permeability defects; interestingly, these sites were solely located within β-strands of the central core of the protein and each resulted in misfolding of the protein. Therefore, no single residue within LptA is responsible for LPS binding, supporting previous EPR spectroscopy data indicating that sites across the entire protein work in concert to bind and transport LPS.

Lipopolysaccharide transport regulates bacterial sensitivity to a cell wall-degrading intermicrobial toxin.

Gram-negative bacteria can antagonize neighboring microbes using a type VI secretion system (T6SS) to deliver toxins that target different essential cellular features. Despite the conserved nature of these targets, T6SS potency can vary across recipient species. To understand the functional basis of intrinsic T6SS susceptibility, we screened for essential Escherichia coli (Eco) genes that affect its survival when antagonized by a cell wall-degrading T6SS toxin from Pseudomonas aeruginosa, Tae1. We revealed genes associated with both the cell wall and a separate layer of the cell envelope, lipopolysaccharide, that modulate Tae1 toxicity in vivo. Disruption of genes in early lipopolysaccharide biosynthesis provided Eco with novel resistance to Tae1, despite significant cell wall degradation. These data suggest that Tae1 toxicity is determined not only by direct substrate damage, but also by indirect cell envelope homeostasis activities. We also found that Tae1-resistant Eco exhibited reduced cell wall synthesis and overall slowed growth, suggesting that reactive cell envelope maintenance pathways could promote, not prevent, self-lysis. Together, our study reveals the complex functional underpinnings of susceptibility to Tae1 and T6SS which regulate the impact of toxin-substrate interactions in vivo.

Discovery, characterization, and redesign of potent antimicrobial thanatin orthologs from Chinavia ubica and Murgantia histrionica targeting E. coli LptA

Podisus maculiventris thanatin has been reported as a potent antimicrobial peptide with antibacterial and antifungal activity. Its antibiotic activity has been most thoroughly characterized against E. coli and shown to interfere with multiple pathways, such as the lipopolysaccharide transport (LPT) pathway comprised of seven different Lpt proteins. Thanatin binds to E. coli LptA and LptD, thus disrupting the LPT complex formation and inhibiting cell wall synthesis and microbial growth. Here, we performed a genomic database search to uncover novel thanatin orthologs, characterized their binding to E. coli LptA using bio-layer interferometry, and assessed their antimicrobial activity against E. coli. We found that thanatins from Chinavia ubica and Murgantia histrionica bound tighter (by 3.6- and 2.2-fold respectively) to LptA and exhibited more potent antibiotic activity (by 2.1- and 2.8-fold respectively) than the canonical thanatin from P. maculiventris. We crystallized and determined the LptA-bound complex structures of thanatins from C. ubica (1.90 Å resolution), M. histrionica (1.80 Å resolution), and P. maculiventris (2.43 Å resolution) to better understand their mechanism of action. Our structural analysis revealed that residues A10 and I21 in C. ubica and M. histrionica thanatin are important for improving the binding interface with LptA, thus overall improving the potency of thanatin against E. coli. We also designed a stapled variant of thanatin that removes the need for a disulfide bond but retains the ability to bind LptA and antibiotic activity. Our discovery presents a library of novel thanatin sequences to serve as starting scaffolds for designing more potent antimicrobial therapeutics.

Lipopolysaccharide as an antibiotic target

Gram-negative bacteria, including Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii are amongst the highest priority drug-resistant pathogens, for which new antibiotics are urgently needed. Whilst antibiotic drug development is inherently challenging, this is particularly true for Gram-negative bacteria due to the presence of the outer membrane, a highly selective permeability barrier that prevents the ingress of several classes of antibiotic. This selectivity is largely due to an outer leaflet composed of the glycolipid lipopolysaccharide (LPS), which is essential for the viability of almost all Gram-negative bacteria. This essentiality, coupled with the conservation of the synthetic pathway across species and recent breakthroughs in our understanding of transport and membrane homeostasis has made LPS an attractive target for novel antibiotic drug development. Several different targets have been explored and small molecules developed that show promising activity in vitro. However, these endeavours have met limited success in clinical testing and the polymyxins, discovered more than 70 years ago, remain the only LPS-targeting drugs to enter the clinic thus far. In this review, we will discuss efforts to develop therapeutic inhibitors of LPS synthesis and transport and the reasons for limited success, and explore new developments in understanding polymyxin mode of action and the identification of new analogues with reduced toxicity and enhanced activity.

Peptidomimetic antibiotics disrupt the lipopolysaccharide transport bridge of drug-resistant Enterobacteriaceae.

The rise of antimicrobial resistance poses a substantial threat to our health system, and, hence, development of drugs against novel targets is urgently needed. The natural peptide thanatin kills Gram-negative bacteria by targeting proteins of the lipopolysaccharide transport (Lpt) machinery. Using the thanatin scaffold together with phenotypic medicinal chemistry, structural data, and a target-focused approach, we developed antimicrobial peptides with drug-like properties. They exhibit potent activity against Enterobacteriaceae both in vitro and in vivo while eliciting low frequencies of resistance. We show that the peptides bind LptA of both wild-type and thanatin-resistant Escherichia coli and Klebsiella pneumoniae strains with low-nanomolar affinities. Mode of action studies revealed that the antimicrobial activity involves the specific disruption of the Lpt periplasmic protein bridge.

Lipopolysaccharide biosynthesis and traffic in the envelope of the pathogen Brucella abortus

Lipopolysaccharide is essential for most Gram-negative bacteria as it is a main component of the outer membrane. In the pathogen Brucella abortus, smooth lipopolysaccharide containing the O-antigen is required for virulence. Being part of the Rhizobiales, Brucella spp. display unipolar growth and lipopolysaccharide was shown to be incorporated at the active growth sites, i.e. the new pole and the division site. By localizing proteins involved in the lipopolysaccharide transport across the cell envelope, from the inner to the outer membrane, we show that the lipopolysaccharide incorporation sites are determined by the inner membrane complex of the lipopolysaccharide transport system. Moreover, we identify the main O-antigen ligase of Brucella spp. involved in smooth lipopolysaccharide synthesis. Altogether, our data highlight a layer of spatiotemporal organization of the lipopolysaccharide biosynthesis pathway and identify an original class of bifunctional O-antigen ligases.

Characterizing the interactions between the LPS transport protein LptC and the ABC transporter LptB2FG.

Synthesis of the essential glycolipid lipopolysaccharide (LPS) in Gram-negative bacteria is completed at the outer leaflet of the inner membrane (IM). Following this process, seven LPS transport (Lpt) proteins facilitate the movement of LPS to the outer membrane (OM). LPS transport to the OM is an essential process and disruption at any stage has detrimental effects on bacterial viability. LptB2FG, the first component of the Lpt system, is a type IV ABC transporter that provides the driving force for LPS extraction from the IM and subsequent transport across a stable protein bridge to the outer leaflet of the OM. LptC is a periplasmic protein anchored to the IM by a single transmembrane helix, which intercalates between the LptF and LptG transmembrane domains, and has been shown to regulate the ATPase activity of LptB2FG. Despite a high level of structural homology between the periplasmic domains of LptF and LptG, the crystal and cryo-EM structures of LptB2FG in complex with LptC show preferential binding of the periplasmic domain of LptC to the periplasmic domain of LptF. Therefore, the role of LptG in this transport process remains unknown. Additionally, we identified six partial loss of function LptC mutations during an in vivo exploratory mutagenesis study. To further investigate the LptB2FGC complex, site-directed spin labeling electron paramagnetic resonance (EPR) spectroscopy, microscale thermophoresis (MST), and an in vitro ATPase assay were employed to characterize differences between the binding partners of periplasmic LptF and LptG along with the mechanistic effects of the LptC loss of function mutants on partner binding and ATPase function or regulation. This work provides evidence suggesting a previously undefined interaction between LptC and LptG while also exploring the role of partial loss of function LptC mutants.

Interactions of polymyxin B1 with the gram-negative inner membrane: A simulation study.

The rise of drug resistant Gram-negative bacterial infections in recent decades has led to increased use of polymyxins, a class of antimicrobial peptides, as a ‘last resort’ treatment. In addition, the recent emergence of polymyxin-resistant strains threatens to bring about an era in which bacteria are resistant to all known antibiotics. It is thus necessary to develop new polymyxin-based antibiotics, but a lack of understanding of how polymyxins work at the molecular level may hinder such efforts. One question that remains open is how do polymyxins interact with the Gram-negative inner membrane to cause cell lysis? It has recently been suggested that polymyxins may target small quantities of the complex glycolipid lipopolysaccharide (LPS) that are present in the inner membrane prior to LPS transport to the outer membrane. In this work, we used a multiscale molecular dynamics (MD) approach including long-timescale, coarse-grained (CG) and atomistic simulations to investigate the interactions of polymyxin B1 (PMB1) with bacterial inner membrane models in the presence of small quantities of LPS. We observed that PMB1 is inserted into the inner membrane and localises at the LPS-phospholipid interface, sampling a wide range of interfacial environments. Our CG simulations also indicate that PMB1-LPS interactions are long-lived and numerous. In the presence of membrane proteins, a small number of PMB1 molecules were observed to form interactions with native inner membrane proteins, reducing the overall probability of PMB1 molecules remaining bound to LPS. Overall, this work indicates that PMB1 can target LPS molecules in the inner membrane, supporting recent hypotheses on its mode of action, while also providing new insights into the effect of membrane proteins upon PMB1-inner membrane interactions.

Identification of a novel transport system in Borrelia burgdorferi that links the inner and outer membranes.

Borrelia burgdorferi, the spirochete that causes Lyme disease, is a diderm organism that is similar to Gram-negative organisms in that it contains both an inner and outer membrane. Unlike typical Gram-negative organisms, however, B. burgdorferi lacks lipopolysaccharide (LPS). Using computational genome analyses and structural modeling, we identified a transport system containing six proteins in B. burgdorferi that are all orthologs to proteins found in the lipopolysaccharide transport (LPT) system that links the inner and outer membranes of Gram-negative organisms and is responsible for placing LPS on the surface of these organisms. While B. burgdorferi does not contain LPS, it does encode over 100 different surface-exposed lipoproteins and several major glycolipids, which like LPS are also highly amphiphilic molecules, though no system to transport these molecules to the borrelial surface is known. Accordingly, experiments supplemented by molecular modeling were undertaken to determine whether the orthologous LPT system identified in B. burgdorferi could transport lipoproteins and/or glycolipids to the borrelial outer membrane. Our combined observations strongly suggest that the LPT transport system does not transport lipoproteins to the surface. Molecular dynamic modeling, however, suggests that the borrelial LPT system could transport borrelial glycolipids to the outer membrane.

Targeting LPS biosynthesis and transport in gram-negative bacteria in the era of multi-drug resistance

Gram-negative bacteria pose a major threat to human health in an era fraught with multi-drug resistant bacterial infections. Despite extensive drug discovery campaigns over the past decades, no new antibiotic target class effective against gram-negative bacteria has become available to patients since the advent of the carbapenems in 1985. Antibiotic discovery efforts against gram-negative bacteria have been hampered by limited intracellular accumulation of xenobiotics, in large part due to the impermeable cell envelope comprising lipopolysaccharide (LPS) in the outer leaflet of the outer membrane, as well as a panoply of efflux pumps. The biosynthesis and transport of LPS are essential to the viability and virulence of most gram-negative bacteria. Thus, both LPS biosynthesis and transport are attractive pathways to target therapeutically. In this review, we summarize the LPS biosynthesis and transport pathways and discuss efforts to find small molecule inhibitors against targets within these pathways.

Melatonin alleviates lead-induced fatty liver in the common carps (Cyprinus carpio) via gut-liver axis

As a widespread aquatic environmental contaminant, Lead (Pb) can provoke hepatic injury in various animals. Melatonin (MT) plays a crucial role in the regulation of inflammatory response. Accumulating evidence elucidates exogenous toxins can elicit hepatic lipid metabolic disorders by influencing the gut microbiome. Nevertheless, the effects of Pb on gut microbiota and hepatic lipid metabolism of the common carps, and whether MT can prevent and cure Pb-induced toxicity via regulating microbiome remains unknown. Here, metagenomic and transcriptomic analysis were subsequently implemented to identify the Pb exposure-triggered prominent alternation of gut-liver signal. In the present study the severe intestinal injury and fatty liver formation caused by Pb in common carp were preliminarily determined. Metagenomic analysis confirmed that the gut microbiome dominant phyla, family and genus of the common carps were Fusobacteria, Fusobacteriaceae and Cetobacterium. Meanwhile, lipopolysaccharide (LPS) biosynthesis pathway was regarded as one of the main responsible for Pb exposure. Subsequently, LPS was demonstrated as the Pb-triggered microbial-derived signal of the common carps by ELISA analysis, and involves in the hepatic metabolic disorders via deteriorating the intestinal barrier. Additionally, it confirmed that hepatocytes ferroptosis associated with Pb-evoked fatty liver of the common carps, and the aggravation of lysosomal dyshomeostasis as well as inhibition of AMPK phosphorylation were referred to lipid metabolic disorders. The results of the present study demonstrated microbial-derived signal induced by aquatic Pb contaminant cause fatty liver formation in the common carps, and the protective effects of MT on Pb toxicity were performed by receding LPS over-synthesis, restraining microbiota-sourced LPS transport, along with attenuation of hepatocytes ferroptosis.

Clinical Significance of Lipid Transport Function of ABC Transporters in the Innate Immune System.

ABC transporters are a large family of proteins that transport a variety of substrates across cell plasma membranes. Because of this, they are involved in many physiological processes. It is of interest to note that many ABC transporters are involved in the transport of various lipids. In addition, this function may be related to the innate immune system. The evidence that ABC transporters are involved in the regulation of the innate immune system through the transport of various substances greatly enhances the understanding of their clinical significance. ABC transporters are involved in the cellular homeostasis of cholesterol as well as in the regulation of its content in lipid rafts. Through these mechanisms, they can regulate the function of membrane proteins, including receptors of the innate immune system. By regulating lipid transport, some members of ABC transporters are involved in phagocytosis. In addition, ABC transporters are involved in the transport of lipopolysaccharide, lipid mediators of inflammation, and perform other functions in the innate immune system.

Impact of High-Density Lipoproteins on Sepsis.

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Here, we review the impact of high-density lipoproteins (HDL) on sepsis from the perspective of biochemistry and pathophysiology, epidemiological research, and intervention studies in animals. Pathogen lipid moieties are major ligands for innate immunity receptors, such as toll-like receptors. The binding of pathogen-associated lipids to lipoproteins leads to sequestration, neutralization, and inactivation of their pro-inflammatory effects. Lipoproteins constitute an arm of the innate immune system. Pathogen-associated lipids can be removed from the body via the reverse lipopolysaccharide transport pathway in which HDL play a key role. Independent of the capacity for sequestration, the direct anti-inflammatory effects of HDL may counteract the development of sepsis. Mendelian randomization research using genetic variants associated with HDL cholesterol as an instrumental variable was consistent with a probable causal relationship between increased HDL cholesterol levels and decreased risk of infectious hospitalizations. Low HDL cholesterol independently predicts an adverse prognosis in sepsis both in observational epidemiology and in Mendelian randomization studies. Several HDL-associated enzymes, including phospholipid transfer protein (PLTP) and cholesterol ester transfer protein (CETP), undergo profound changes during sepsis. Potential HDL-directed interventions for treatment of sepsis include apolipoprotein A-I-based therapies, recombinant PLTP, and CETP inhibition.

Crystal structure of Campylobacter jejuni lipoprotein Cj1090c.

In Gram-negative bacteria, lipopolysaccharide (LPS) is an essential component of the asymmetric outer membrane (OM). LptE is an OM lipoprotein that forms a complex with the β-barrel OM protein, LptD. Incorporation of LPS into the OM outer leaflet is essential for bacterial viability, and mediated by the LptD/E complex. The genome of Campylobacter jejuni, a major foodborne pathogen, contains over 20 putative lipoproteins including Cj1090c. Here, we report the crystal structure of Cj1090c at 2.4 Å resolution, revealing structural evidence for LptE in C. jejuni. The analysis of this crystal structure, along with the genomic context, allows us to propose the C. jejuni LPS transport system for the first time, and permits for discussion of the features of the LptD/E complex of C. jejuni.