1,721,086 research outputs found
Evaluation of (acyloxy)alkyl ester linkers for antibiotic release from siderophore–antibiotic conjugates
No full textThe syntheses of five ciprofloxacin-modified (acyloxyl)alkyl esters and two siderophore–ciprofloxacin conjugates based on enterobactin that harbor such hydrolyzable linkages are reported. The hydrolytic stabilities of ciprofloxacin-modified (acyloxy)alkyl esters, evaluated at pH 7.5 and 30 °C, vary by >370-fold depending on the substituents in the vicinity of the ester linkage
High-Affinity Manganese Coordination by Human Calprotectin Is Calcium-Dependent and Requires the Histidine-Rich Site Formed at the Dimer Interface
No full textCalprotectin (CP) is a transition metal-chelating antimicrobial protein of the calcium-binding S100 family that is produced and released by neutrophils. It inhibits the growth of various pathogenic microorganisms by sequestering the transition metal ions manganese and zinc. In this work, we investigate the manganese-binding properties of CP. We demonstrate that the unusual His[subscript 4] motif (site 2) formed at the S100A8/S100A9 dimer interface is the site of high-affinity Mn(II) coordination. We identify a low-temperature Mn(II) spectroscopic signal for this site consistent with an octahedral Mn(II) coordination sphere with simulated zero-field splitting parameters D = 270 MHz and E/D = 0.30 (E = 81 MHz). This analysis, combined with studies of mutant proteins, suggests that four histidine residues (H17 and H27 of S100A8; H91 and H95 of S100A9) coordinate Mn(II) in addition to two as-yet unidentified ligands. The His[subscript 3]Asp motif (site 1), which is also formed at the S100A8/S100A9 dimer interface, does not provide a high-affinity Mn(II) binding site. Calcium binding to the EF-hand domains of CP increases the Mn(II) affinity of the His[subscript 4] site from the low-micromolar to the mid-nanomolar range. Metal-ion selectivity studies demonstrate that CP prefers to coordinate Zn(II) over Mn(II). Nevertheless, the specificity of Mn(II) for the His[subscript 4] site provides CP with the propensity to form mixed Zn:Mn:CP complexes where one Zn(II) ion occupies site 1 and one Mn(II) ion occupies site 2. These studies support the notion that CP responds to physiological calcium ion gradients to become a high-affinity transition metal ion chelator in the extracellular space where it inhibits microbial growth.Kinship Foundation. Searle Scholars ProgramMassachusetts Institute of Technology. Center for Environmental Health Sciences (NIH P30-ES002109)Massachusetts Institute of Technology. Dept. of ChemistryNational Science Foundation (U.S.) (Grant NSF-0070319)National Institutes of Health (U.S.) (Grant NIH GM68762
Defensins, lectins, mucins, and secretory immunoglobulin A: microbe-binding biomolecules that contribute to mucosal immunity in the human gut
No full textIn the intestine, the mucosal immune system plays essential roles in maintaining homeostasis between the host and microorganisms, and protecting the host from pathogenic invaders. Epithelial cells produce and release a variety of biomolecules into the mucosa and lumen that contribute to immunity. In this review, we focus on a subset of these remarkable host-defense factors–enteric α-defensins, select lectins, mucins, and secretory immunoglobulin A–that have the capacity to bind microbes and thereby contribute to barrier function in the human gut. We provide an overview of the intestinal epithelium, describe specialized secretory cells named Paneth cells, and summarize our current understanding of the biophysical and functional properties of these select microbe-binding biomolecules. We intend for this compilation to complement prior reviews on intestinal host-defense factors, highlight recent advances in the field, and motivate investigations that further illuminate molecular mechanisms as well as the interplay between these molecules and microbes.National Institutes of Health (U.S.) (Grant DP2OD007045
Siderophore-based detection of Fe(iii) and microbial pathogens
Get PDFSiderophores are low-molecular-weight iron chelators that are produced and exported by bacteria, fungi and plants during periods of nutrient deprivation. The structures, biosynthetic logic, and coordination chemistry of these molecules have fascinated chemists for decades. Studies of such fundamental phenomena guide the use of siderophores and siderophore conjugates in a variety of medicinal applications that include iron-chelation therapies and drug delivery. Sensing applications constitute another important facet of siderophore-based technologies. The high affinities of siderophores for both ferric ions and siderophore receptors, proteins expressed on the cell surface that are required for ferric siderophore import, indicate that these small molecules may be employed for the selective capture of metal ions, proteins, and live bacteria. This minireview summaries progress in methods that utilize native bacterial and fungal siderophore scaffolds for the detection of Fe(III) or microbial pathogens.Massachusetts Institute of Technology. Dept. of Chemistr
Beyond iron: non-classical biological functions of bacterial siderophores
Get PDFBacteria secrete small molecules known as siderophores to acquire iron from their surroundings. For over 60 years, investigations into the bioinorganic chemistry of these molecules, including fundamental coordination chemistry studies, have provided insight into the crucial role that siderophores play in bacterial iron homeostasis. The importance of understanding the fundamental chemistry underlying bacterial life has been highlighted evermore in recent years because of the emergence of antibiotic-resistant bacteria and the need to prevent the global rise of these superbugs. Increasing reports of siderophores functioning in capacities other than iron transport have appeared recently, but reports of “non-classical” siderophore functions have long paralleled those of iron transport. One particular non-classical function of these iron chelators, namely antibiotic activity, was documented before the role of siderophores in iron transport was established. In this Perspective, we present an exposition of past and current work into non-classical functions of siderophores and highlight the directions in which we anticipate that this research is headed. Examples include the ability of siderophores to function as zincophores, chalkophores, and metallophores for a variety of other metals, sequester heavy metal toxins, transport boron, act as signalling molecules, regulate oxidative stress, and provide antibacterial activity.National Institutes of Health (U.S.) (R21 A1101784
Targeting virulence: salmochelin modification tunes the antibacterial activity spectrum of β-lactams for pathogen-selective killing of Escherichia coli
No full textNew antibiotics are required to treat bacterial infections and counteract the emergence of antibiotic resistance. Pathogen-specific antibiotics have several advantages over broad-spectrum drugs, which include minimal perturbation to the commensal microbiota. We present a strategy for targeting antibiotics to bacterial pathogens that utilises the salmochelin-mediated iron uptake machinery of Gram-negative Escherichia coli. Salmochelins are C-glucosylated derivatives of the siderophore enterobactin. The biosynthesis and utilisation of salmochelins are important for virulence because these siderophores allow pathogens to acquire iron and evade the enterobactin-scavenging host-defense protein lipocalin-2. Inspired by the salmochelins, we report the design and chemoenzymatic preparation of glucosylated enterobactin–β-lactam conjugates that harbour the antibiotics ampicillin (Amp) and amoxicillin (Amx), hereafter GlcEnt–Amp/Amx. The GlcEnt scaffolds are based on mono- and diglucosylated Ent where one catechol moiety is functionalized at the C5 position for antibiotic attachment. We demonstrate that GlcEnt–Amp/Amx provide up to 1000-fold enhanced antimicrobial activity against uropathogenic E. coli relative to the parent β-lactams. Moreover, GlcEnt–Amp/Amx based on a diglucosylated Ent (DGE) platform selectively kill uropathogenic E. coli that express the salmochelin receptor IroN in the presence of non-pathogenic E. coli and other bacterial strains that include the commensal microbe Lactobacillus rhamnosus GG. Moreover, GlcEnt–Amp/Amx evade the host-defense protein lipocalin-2, and exhibit low toxicity to mammalian cells. Our work establishes that siderophore–antibiotic conjugates provide a strategy for targeting virulence, narrowing the activity spectrum of antibiotics in clinical use, and achieving selective delivery of antibacterial cargos to pathogenic bacteria on the basis of siderophore receptor expression.Massachusetts Institute of Technology. Department of ChemistryNational Institutes of Health (U.S.) (Pacific Southwest Research Center of Excellence for Biodefense and Emerging Infectious Disease)Kinship Foundation. Searle Scholars ProgramRoyal Thai Government (RTG) (Scholarship program
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Human α-Defensin 6: A Small Peptide That Self-Assembles and Protects the Host by Entangling Microbes
Get PDFConspectus Human α-defensin 6 (HD6) is a 32-residue cysteine-rich peptide that contributes to innate immunity by protecting the host at mucosal sites. This peptide is produced in small intestinal Paneth cells, stored as an 81-residue precursor peptide named proHD6 in granules, and released into the lumen. One unusual feature of HD6 is that it lacks the broad-spectrum antimicrobial activity observed for other human α-defensins, including the Paneth cell peptide human α-defensin 5 (HD5). HD6 exhibits unprecedented self-assembly properties, which confer an unusual host-defense function. HD6 monomers self-assemble into higher-order oligomers termed “nanonets”, which entrap microbes and prevent invasive gastrointestinal pathogens such as Salmonella enterica serovar Typhimurium and Listeria monocytogenes from entering host cells. One possible advantage of this host-defense mechanism is that HD6 helps to keep microbes in the lumen such that they can be excreted or attacked by other components of the immune system, such as recruited neutrophils. In this Account, we report our current understanding of HD6 and focus on work published since 2012 when Bevins and co-workers described the discovery of HD6 nanonets in the literature. First, we present studies that address the biosynthesis, storage, and maturation of HD6, which demonstrate that nature uses a propeptide strategy to spatially and temporally control the formation of HD6 nanonets in the small intestine. The propeptide is stored in Paneth cell granules, and proteolysis occurs during or following release into the lumen, which affords the 32-residue mature peptide that self-assembles. We subsequently highlight structure-function studies that provide a foundation for understanding the molecular basis for why HD6 exhibits unusual self-assembly properties compared with other characterized defensins. The disposition of hydrophobic residues in the HD6 primary structure differs from that of other human α-defensins and is an important structural determinant for oligomerization. Lastly, we consider functional studies that illuminate how HD6 contributes to mucosal immunity. We recently discovered that in addition to blocking bacterial invasion into host epithelial cells by Gram-negative and Gram-positive gastrointestinal pathogens, HD6 suppresses virulence traits displayed by the opportunistic human fungal pathogen Candida albicans. In particular, we found that C. albicans biofilm formation, which causes complications in the treatment of candidiasis, is inhibited by HD6. This observation suggests that HD6 may contribute to intestinal homeostasis by helping to keep C. albicans in its commensal state. We intend for this Account to inspire further biochemical, biophysical, and biological investigations that will advance our understanding of HD6 in mucosal immunity and the host-microbe interaction.National Institutes of Health (U.S.) (Grant DP2OD007045
Transition Metals at the Host–pathogen Interface: How Neisseria Exploit Human Metalloproteins for Acquiring Iron and Zinc
No full textTransition metals are essential nutrients for all organisms and important players in the host-microbe interaction. During bacterial infection, a tug-of-war between the host and microbe for nutrient metals occurs: the host innate immune system responds to the pathogen by reducing metal availability and the pathogen tries to outmaneuver this response. The outcome of this competition, which involves metal-sequestering host-defense proteins and microbial metal acquisition machinery, is an important determinant for whether infection occurs. One strategy bacterial pathogens employ to overcome metal restriction involves hijacking abundant host metalloproteins. The obligate human pathogens Neisseria meningitidis and N. gonorrhoeae express TonB-dependent transport systems that capture human metalloproteins, extract the bound metal ions, and deliver these nutrients into the bacterial cell. This review highlights structural and mechanistic investigations that provide insights into how Neisseria acquire iron from the Fe(III)-transport protein transferrin (TF), the Fe(III)-chelating host-defense protein lactoferrin (LF), and the oxygen-transport protein hemoglobin (Hb), and obtain zinc from the metal-sequestering antimicrobial protein calprotectin (CP).National Institutes of Health (U.S.) (Grant 1R01AI114625)National Institutes of Health (U.S.) (Grant 1R21AI126465)National Science Foundation (U.S.) (Grant CHE-1352132
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