Lipid II: total synthesis of the bacterial cell wall precursor and utilization as a substrate for glycosyltransfer and transpeptidation by penicillin binding protein (PBP) 1b of Escherichia coli.

An essential feature in the life cycle of both gram positive and gram negative bacteria is the production of new cell wall. Also known as murein, the cell wall is a two-dimensional polymer, consisting of a linear, repeating N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) motif, cross-linked via peptides appended to MurNAc. The final steps in the maturation of murein are catalyzed by a single, bifunctional enzyme, known as a high MW, class A penicillin binding protein (PBP). PBPs catalyze polymerization of the sugar units (glycosyltransfer), as well as peptide cross-linking (transpeptidation) utilizing Lipid II as substrate. Detailed enzymology on this enzyme has been limited, due to difficulties in obtaining sufficient amounts of Lipid II, as well as the availability of a convenient and informative assay. We report the total chemical synthesis of Lipid II, as well as the development of an appropriate assay system and the observation of both catalytic transformations.     

In Vivo Probe of Lipid II‐Interacting Proteins

β‐Lactams represent one of the most important classes of antibiotics discovered to date. These agents block Lipid II processing and cell wall biosynthesis through inactivation of penicillin‐binding proteins (PBPs). PBPs enzymatically load cell wall building blocks from Lipid II carrier molecules onto the growing cell wall scaffold during growth and division. Lipid II, a bottleneck in cell wall biosynthesis, is the target of some of the most potent antibiotics in clinical use. Despite the immense therapeutic value of this biosynthetic pathway, the PBP–Lipid II association has not been established in live cells. To determine this key interaction, we designed an unnatural d ‐amino acid dipeptide that is metabolically incorporated into Lipid II molecules. By hijacking the peptidoglycan biosynthetic machinery, photoaffinity probes were installed in combination with click partners within Lipid II, thereby allowing, for the first time, demonstration of PBP interactions in vivo with Lipid II.     

Structure of Lipid A from Pseudomonas corrugata by electrospray ionization quadrupole time-of-flight tandem mass spectrometry

The use of the electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOFMS) technique for the structural determination of Lipid A from Pseudomonas corrugata is described. This technique appears to be more sensitive with respect to other commonly used tandem mass spectrometric approaches, and was very valuable in the structural determination of the highly heterogeneous Lipid A fractions. The Lipid A fraction consists mainly of a pentaacyl component in which 3-hydroxydecanoyl [10:0(3-OH)] and 3-hydroxydodecanoyl [12:0(3-OH)] are linked as primary acyl substituents to the classical bisphosphorylated beta-(1' --> 6)-linked D-glucosamine disaccharide. Secondary substitution of N-acyl fatty acids with dodecanoyl residues [12:0] and/or its 2-OH derivatives was also observed.     

Lipid vesicles as possible intermediates in the origin of life

Lipid vesicles (liposomes) are closed structures in which (at least) one lipid bilayer separates an aqueous inner compartment from the bulk external aqueous medium, as in membranes of contemporary biological cells. Lipid vesicles have therefore been considered as possible cell precursors during the prebiological era on Earth. Recently, it has been shown that lipid vesicles form spontaneously. Furthermore, it has been demonstrated that thermodynamically controlled peptide binding to and controlled polymerization reactions on vesicles are possible, thus leading to an increase in the molecular complexity of lipid vesicles. This may have been relevant during the prebiological evolution. © 1999 Elsevier Science Ltd.     

Loosening of Lipid Packing Promotes Oligoarginine Entry into Cells

Despite extensive use of arginine‐rich cell‐penetrating peptides (CPPs)—including octaarginine (R8)—as intracellular delivery vectors, mechanisms for their internalization are still under debate. Lipid packing in live cell membranes was characterized using a polarity‐sensitive dye (di‐4‐ANEPPDHQ), and evaluated in terms of generalized polarization. Treatment with membrane curvature‐inducing peptides led to significant loosening of the lipid packing, resulting in an enhanced R8 penetration. Pyrenebutyrate (PyB) is known to facilitate R8 membrane translocation by working as a hydrophobic counteranion. Interestingly, PyB also actively induced membrane curvature and perturbed lipid packing. R8 is known to directly cross cell membranes at elevated concentrations. The sites of R8 influx were found to have looser lipid packing than surrounding areas. Lipid packing loosening is proposed as a key factor that governs the membrane translocation of CPPs.     

Ramoplanin inhibits bacterial transglycosylases by binding as a dimer to lipid II

Ramoplanin is a lipglycodepsipeptide antibiotic that inhibits peptidoglycan biosynthesis. Its mechanism of action has been the subject of debate. It was originally proposed to inhibit the MurG step of peptidoglycan synthesis by binding Lipid I. In this paper, we report that ramoplanin inhibits bacterial transglycosylases by binding to Lipid II, the substrate for these enzymes. The inhibition curves reveal that the inhibitory species has a stoichiometry of 2:1 ramoplanin:Lipid II. A Job titration confirms that ramoplanin binds as a dimer to Lipid II. The apparent dissociation constant is in the nanomolar range, which is unusually low given the nature of the interacting species. We show that Lipid II binding is coupled to the formation of a higher order species, which may explain the tight binding. We also present a testable model for the binding-competent dimeric conformation of ramoplanin.     

A Time-Resolved FRET Assay Identifies a Small Molecule that Inhibits the Essential Bacterial Cell Wall Polymerase FtsW

The peptidoglycan cell wall is essential for bacterial survival. To form the cell wall, peptidoglycan glycosyltransferases (PGTs) polymerize Lipid II to make glycan strands and then those strands are crosslinked by transpeptidases (TPs). Recently, the SEDS (for shape, elongation, division, and sporulation) proteins were identified as a new class of PGTs. The SEDS protein FtsW, which produces septal peptidoglycan during cell division, is an attractive target for novel antibiotics because it is essential in virtually all bacteria. Here, we developed a time-resolved Förster resonance energy transfer (TR-FRET) assay to monitor PGT activity and screened a Staphylococcus aureus lethal compound library for FtsW inhibitors. We identified a compound that inhibits S. aureus FtsW in vitro. Using a non-polymerizable Lipid II derivative, we showed that this compound competes with Lipid II for binding to FtsW. The assays described here will be useful for discovering and characterizing other PGT inhibitors.     

Lipid characterization of embryo zones by silica plate laser desorption ionization mass spectrometry imaging (SP-LDI-MSI)

Lipid pathways play important biological roles in mammalian embryology, directing early developmental pathways to differentiation. Phospholipids and triglycerides, among others, are the main composing lipids of zona pellucida in several embryo species. Lipid analysis in embryos by mass spectrometry usually requires sample preparation and/or matrix application. This novel approach using silica plate laser desorption/ionization mass spectrometry imaging (SP-LDI-MSI) allows direct single-cell imaging and embryo region discrimination with no matrix coating. Its application is herein described for two- and eight-cell embryos. Lipid biomarkers for blastomere and intact zona pellucida are reported and corroborated by both fragmentation reactions (MS/MS) and images. Results obtained in this work are understood to be of great use for further developments on in vitro bovine fertilization. Since much of the processes can be monitored by characteristic biomarkers, it is now possible to precisely identify cell division errors during early embryo stages, as well as evaluate pre-implantation conditions.     

Application of the Weisz Ring oven technique to the separation and identification of micro-quantities of some less familiar cations

Summary Use of the ring oven in separation and identification of mixtures of less familiar metal ions has been described. Separation of metal ions from the following mixtures has successfully been carried out: 1. UO₂(II) and Th(IV), 2. Th(IV) and Ce(IV), 3. Pd(II) and Au(III), 4. Pt(IV) and Au(III), 5. Ce(III) and Ce(IV), 6. UO₂(II), Th(IV) and Ti(IV), 7. Th(IV), Ti(IV) and Ce(IV), 8. Th(IV), Ce(IV) and Zr(IV), 9. Ti(IV), V(V) and Zr(IV), 10. Mo(VI), V(V) and W(VI) and 11. Be(II), Al(III) and Mg(II). In the case of binary mixtures, the separation was in the form of a central spot and a concentric ring; in ternary mixtures the metals were precipitated in a central spot and two concentric rings.

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Zusammenfassung Zur Trennung und Identifizierung folgender Gemische seltenerer Metallionen wurde der Ringofen mit Erfolg verwendet: 1. UO₂(II) und Th(IV), 2. Th(IV) und Ce(IV), 3. Pd(II) und Au(III), 4. Pt(IV) und Au(III), 5. Ce(III) und Ce(IV), 6. UO₂(II), Th(IV) und Ti(IV), 7. Th(IV), Ti(IV) und Ce(IV). 8. Th(IV), Ce(IV) und Zr(IV), 9. Ti(IV), V(V) und Zr(IV), 10. Mo(VI), V(V) und W(VI) und 11. Be(II), Al(III) und Mg(II). Bei binären Gemischen erfolgt die Trennung in einen zentralen Fleck und einen Ring, bei ternären Mischungen in einen Fleck und zwei konzentrische Ringe.

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Résumé On a décrit l'utilisation du four annulaire pour la séparation et l'identification de mélanges d'ions métalliques moins courants. On a effectué la séparation des ions métalliques à partir des mélanges suivants: 1. UO₂(II) et Th(IV), 2. Th(IV) et Ce(IV), 3. Pd(II) et Au(III), 4. Pt(IV) et Au(III), 5. Ce(III) et Ce(IV), 6. UO₂(II), Th(IV) et Ti(IV), 7. Th(IV), Ti(IV) et Ce(IV), 8. Th(IV), Ce(IV) et Zr(IV), 9. Ti(IV), V(V) et Zr(IV), 10. Mo(VI), V(V) et W(VI) et 11. Be(II), Al(III) et Mg(II). Dans le cas des mélanges binaires, la séparation se présentait sous forme d'une tache centrale et d'un anneau concentrique; chez les mélanges ternaires, les métaux étaient précipités en une tache centrale et deux anneaux concentriques.

     

Synthesis and structural characterization of bi- and trimetallic octacyanometalate(IV) complexes: [Delta,Lambda-MII(en)3][cis-MII(en)2(OH2)][MIV(CN)8].2H2O and [cis-MII(en)2(OH2)]2[(mu-NC)2MIV(CN)6].4H2O (MII = Mn, Co, Ni; MIV = Mo, W)

Treatment of [M(II)(en)(3)][OTs](2) or methanolic ethylenediamine solutions containing transition metal p-toluenesulfonates (M(II) = Mn, Co) with aqueous K(4)M(IV)(CN)(8).2H(2)O or Cs(3)M(V)(CN)(8) (M(IV) = Mo, W; M(V) = Mo) affords crystalline clusters of [M(II)(en)(3)][cis-M(II)(en)(2)(OH(2))(mu-NC)M(IV)(CN)(7)].2H(2)O (M(IV) = Mo; M(II) = Mn, 1; Ni, 5; M(IV) = W; M(II) = Mn, 2; Ni, 6) and [cis-M(II)(en)(2)(OH(2))](2)[(mu-NC)(2)M(IV)(CN)(6)].4H(2)O (M(IV) = Mo; M(II) = Co, 3; Ni, 7; M(IV) = W; M(II) = Co, 4) stoichiometry. Each cluster contains cis-M(II)(en)(2)(OH(2))(mu-NC)(2+) units that likely result from dissociative loss of en from [M(II)(en)(3)](2+), affording cis-M(II)(en)(2)(OH(2))(2)(2+) intermediates that are trapped by M(IV)(CN)(8)(4-).     

脂质与健脑

脂质是人类的基本营养物质之一,是最重要的健脑营养素。本文介绍了脑的发育特点与脂代谢的关系;脂质的结构和分类,以及脂质的健脑益智作用。旨在正确认识脂类,科学摄取脂类,提高智力,促进素质教育。     

An Approach to the Synthesis of Four Rhodomicrobium Vannielii Lipid a Analogues

Abstract

The preparation of four Rh. Vannielii Lipid A analogues (i.e. compounds 22, 23, 30 and 33) is described. Non-neighbouring group supported introduction of the β-glycosidic linkages was performed by coupling the mannopyranosyl bromide 2 and the 2-azido-2-deoxy-glucopyranosyl bromides 10 and 13 with the suitably protected glycosyl acceptors 3, 4 and 5 in the presence of a heterogeneous silver catalyst, to give compounds 6, 7, 14 and 24, respectively. Selective removal of the ally1 group and reduction of the azido functions followed by several O,N-acylation steps afforded, after complete deblocking, the tri-and disaccharide Rh. Vannielii Lipid A analogues 22, 23, 30 and 33.     

First electrogeneration of a platinum(IV) porphyrin: elucidation of the Pt(II/IV) and Pt(IV/II) oxidation-reduction processes in nonaqueous media

The first example for electrogeneration of a Pt(IV) porphyrin from its Pt(II) form is presented and the Pt(II/IV) and reverse Pt(IV/II) oxidation-reduction processes are elucidated by electrochemistry and thin-layer UV-visible spectroelectrochemistry. Three products, [(TPP˙(+))Pt(II)](+), [(TPP)Pt(IV)](2+) and [(TPP˙(+))Pt(IV)](3+), produced by electrooxidation of the Pt(II) porphyrin have been characterized by in situ spectroelectrochemistry and ESR measurements after controlled potential bulk electrolysis. The first definitive evidence for the electrochemical conversion of a Pt(iv) porphyrin to its Pt(II) form is also presented. The potential for this electroreduction is highly dependent upon the nature of the anion, ClO(4)(-) or Cl(-). A mechanism for the reversible conversion between Pt(II) and Pt(IV) tetraphenylporphyrins is proposed.     

Electron Transfer Studies of TIN(IV)/TIN(II) in Acid Media

Abstract

Cyclic voltammaetry of mixed tin(II)/tin(IV) solutions was investigated in 6M HCl on gold and mercury electrodes. It was found that the reduction of tin(II) to tin(iv) proceeded irreversibly while tin(II) to tin(IV) was reversible. Two forms of tin(IV) are postulated. The peak potential for the reduction of tin(IV) was a function of both tin(II) and tin(IV) while that for the oxidation of tin(II) was a function only of tin(II) concentration Potentials for all oxidations and reductions were a function of potential scan rate.     

Voltammetric determination of zirconium using azo compounds

The Optimum oconditions for zirconium complexation with azo compounds are found. The applicability of Eriochrome Red B, Calcon, and Calcion to the voltammetric determination of zirconium, total Zr(IV) and Hf(IV), and Zr(IV) in the presence of Zn(II), Cu(II), Cd(II), Ni(II), or Ti(IV) is demonstrated. The developed procedures are used to determine zirconium in a terbium alloy and in an alloy for airplane wheel drums.     

Synthesis and Metal Collecting Properties of Mono,Di, Tri and Tetramine Based on Silica Gel Matrix

Abstract

Silica gels, chemically modified with mono, di, tri and tetramine (I - IV), were synthesized. The monoamine (I) was produced directly via the reaction of silica gel with 3-aminopropyltrimethoxysilane. The diamine (II), triamine (III) and tetramine (IV) were produced through the reaction of ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA) with 3-chloropropyltrichloromethane modified silica gel, respectively. The sorption properties of the phases (I - IV) toward Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) were investigated at different pH-values based on the batch equilibrium technique, The, metal uptake capacities (mmol/g) were determined and discussed in terms of the structure of the aliphatic amines and the increasing number of nitrogen donor atoms. The metal capacity values demonstrate the higher efficiency of phases III and IV than phases I and II for preconcentration of such metal ions. Moreover, the use of phases III and IV for selective extraction of Cu(II) and Ni(II) is promising.     

Anion-exchange behavior of various metals in hydrazoic acid media

The adsorption characteristics for 43 metals on a strongly basic ion-exchange resin Bio-Rad AG1 were examined in 0.5 M hydrazoic acid solution. The distribution coefficients for V(IV), Fe(III), Cu(II), Zn, Se(IV), Mo(VI), Pd(II), Cd, In(III), Rc(VII), Hg(II) and U(VI), which showed very strong adsorption except for Cd, were measured as a function of hydrazoic acid concentration over the range 0.05–0.5 M. Favorable differences in the distribution coefficients allow useful two- and three-component separations such as Co(II)-Fe(III), As(III)-V(IV), Cd-Zn, Cd- Hg(II), Te(IV)-Se(IV), Th-U(VI), Mn(II)-Mo(VI)-Re(VII), to be achieved on a small column.     

Functional analysis of the lipoglycodepsipeptide antibiotic ramoplanin

The peptide antibiotic ramoplanin is highly effective against several drug-resistant gram-positive bacteria, including vancomycin-resistant Enterococcus faecium (VRE) and methicillin-resistant Staphylococcus aureus (MRSA), two important opportunistic human pathogens. Ramoplanin inhibits bacterial peptidoglycan (PG) biosynthesis by binding to Lipid intermediates I and II at a location different than the N-acyl-D-Ala-D-Ala dipeptide site targeted by vancomycin. Lipid I/II capture physically occludes these substrates from proper utilization by the late-stage PG biosynthesis enzymes MurG and the transglycosylases. Key structural features of ramoplanin responsible for antibiotic activity and PG molecular recognition have been discovered by antibiotic semisynthetic modification in conjunction with NMR analyses. These results help define a minimalist ramoplanin pharmacophore and introduce the possibility of generating ramoplanin-derived peptide or peptidomimetic antibiotics for use against VRE, MRSA, and related pathogens.     

Ion flotation behaviour of thirty-one metal ions in mixed hydrochloric/nitric acid solutions

The ion flotation of 31 metal ions in hydrochloric/nitric acid solution with the cationic surfactant cetylpyridinium chloride was investigated. A 25-ml portion of 0.27-2.87 x 10(-4)M metal ion and 1.8-6.0 x 10(-4)M cetylpyridinium chloride solution in 0.17-3.4M acid mixture ([HCl]:[HNO(3)] = 2.4:1) was subjected to flotation in a cell, 22.5 cm high and 4.0 cm in diameter, for 5 min, with nitrogen bubbles. Ir(IV), Pt(IV), Ge(IV), Sn(IV), Bi(III), Au(III), Tl(III), Pd(II) and Sn(II) were floated from solution in 95-100% yield; Ru(III), Rh(III), Ir(III), Hg(II), Ag(I) and Tl(I) were partly floated, while Cr(VI), Ti(IV), Zr(IV), Ga(III), In(III), Fe(III), Sb(III), Al(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), CD(II) and Pb(II) were floated with less than 20% yield. The flotation behaviour of these metal ions in the mixed acid system was compared with that in hydrochloric acid. The flotation is more efficient in the mixed acid system.