The peptide alkaloid Anachelin: NMR spectroscopic evidence for β-Turn formation in aqueous solution

Anachelin, a complex secondary metabolite isolated from Anabaena cylindrica, possesses an unusual structure combining polyketide, peptide and alkaloid building blocks. This natural product was postulated to act as siderophore with catecholate and salicylate groups for putative iron binding with the three-dimensional solution structure of anachelin remaining unknown. In this preliminary communication, the conformation of anachelin in aqueous solution is investigated. ROESY experiments revealed several interresidual NOEs characteristic of a compact,folded structure. A β-turn type structure of the central tripeptide sequence L-Thr-D-Ser-L-Ser structure involving D-Ser at position (i+1) and L-Ser at position (i+2) would be in agreement with the observed experimental data. In particular, this conformation of the free ligand would align the putative metal binding groups (structural preorganization)and thus lower the free energy for Fe binding. As it is highly unusual to see such a small tripeptide fragment folding into a compact structure, it appears reasonable to assume that both the cationic tetrahydroquinolinium ring as well as the trihydroxylated ε-amino acid contribute to the stabilization of the folded structure

Impaired maturation of the siderophore pyoverdine chromophore in Pseudomonas fluorescens ATCC 17400 deficient for the cytochrome c biogenesis protein CcmC

AbstractPyoverdines are the main siderophores of fluorescent pseudomonads. They comprise a quinoline chromophore, a peptide chain, and a dicarboxylic acid or a dicarboxylic acid amide side chain. Each Pseudomonas species produces a pyoverdine with a different peptide chain. A cytochrome c biogenesis ΔccmC mutant of Pseudomonas fluorescens ATCC 17400 produces multiple pyoverdine forms, showing differences at the level of the chromophore or the side chain. When grown in the presence of L-cysteine, ΔccmC produces only ferribactin, a non-fluorescent precursor of pyoverdine, while addition of oxidized glutathione improves pyoverdine production. We suggest that the conversion of ferribactin to pyoverdine does not take place in the ΔccmC mutant because of lack of oxidizing power in the periplasm

Gas phase kinetics of metal ion ligation by pyrene

Investigation of simple ligation reactions of metal M+ ions with pyrene (Py) within the ICR FT mass spectrometer indicates relatively fast consecutive formation of MPy+ and MPy2+ ions, and if E-i(M+) > E-i(Py) accompanied also by formation of Py+ due to charge exchange. The much slower reaction and equilibrium Py+ + Py reversible arrow Py-2(+), for which the thermodynamic parameters are known, makes it possible to determine the concentration of Py during the ligation reactions and to calculate the second order rate constants from the set of pseudo first order constants obtained by iterative nonlinear least square fitting of experimental snapshot mass spectral data with the proposed kinetic scheme

Genomic, genetic and structural analysis of pyoverdine-mediated iron acquisition in the plant growth-promoting bacterium Pseudomonas fluorescens SBW25

<p>Abstract</p> <p>Background</p> <p>Pyoverdines (PVDs) are high affinity siderophores, for which the molecular mechanisms of biosynthesis, uptake and regulation have been extensively studied in <it>Pseudomonas aeruginosa </it>PAO1. However, the extent to which this regulatory model applies to other pseudomonads is unknown. Here, we describe the results of a genomic, genetic and structural analysis of pyoverdine-mediated iron uptake by the plant growth-promoting bacterium <it>P. fluorescens </it>SBW25.</p> <p>Results</p> <p><it>In silico </it>analysis of the complete, but un-annotated, SBW25 genome sequence identified 31 genes putatively involved in PVD biosynthesis, transport or regulation, which are distributed across seven different regions of the genome. PVD gene iron-responsiveness was tested using '<it>lacZ </it>fusions to five PVD loci, representative of structural and regulatory genes. Transcription of all fusions increased in response to iron starvation. <it>In silico </it>analyses suggested that regulation of <it>fpvR </it>(which is predicted to encode a cytoplasmic membrane-spanning anti-sigma factor) may be unique. Transcriptional assays using gene expression constructs showed that <it>fpvR </it>is positively regulated by FpvI (an extracytoplasmic family (ECF) sigma factor), and not directly by the ferric uptake regulator (Fur) as for PAO1. Deletion of <it>pvdL</it>, encoding a predicted non-ribosomal peptide synthetase (NRPS) involved in PVD chromophore biosynthesis confirmed the necessity of PvdL for PVD production and for normal growth in iron-limited media. Structural analysis of the SBW25 PVD shows a partly cyclic seven residue peptide backbone, identical to that of <it>P. fluorescens </it>ATCC13525. At least 24 putative siderophore receptor genes are present in the SBW25 genome enabling the bacterium to utilize 19 structurally distinct PVDs from 25 different <it>Pseudomonas </it>isolates.</p> <p>Conclusion</p> <p>The genome of <it>P. fluorescens </it>SBW25 contains an extensively dispersed set of PVD genes in comparison to other sequenced <it>Pseudomonas </it>strains. The PAO1 PVD regulatory model, which involves a branched Fpv signaling pathway, is generally conserved in SBW25, however there is a significant difference in <it>fpvR </it>regulation. SBW25 produces PVD with a partly cyclic seven amino acid residue backbone, and is able to utilize a wide variety of exogenous PVDs.</p

The ortho-quinol acetates (die ortho-Chinolacetate): 20 years of dedicated research in Vienna and what happened then?

o-Quinol acetates (o-Chinolacetate) were the main research field of the Organic Chemistry Institute in Vienna (Austria) for two decades beginning in 1950. The possibility to react them with various kinds of compounds was exploited for the synthesis of structural types not easily accessible on other ways. They became the basis for investigations, e.g. in photochemistry, in reaction mechanistic studies of various rearrangement reactions, or the Diels-Alder reaction. Even in the natural products chemistry o-quinol structures can be found comprising Diels-Alder dimeric terpenes. Most of the original publications had appeared in Monatshefte fur Chemie written in German. This might explain a statement from the year 2000 that These findings add to our knowledge of the largely unexplored chemistry of o-quinolsaEuro broken vertical bar. (Nicolaou et al. in J Am Chem Soc 122:3071, 2000). This review is intended to wake up slumbering knowledge

Structure clucidation of natural products by mass spectrometry

xi, 233 p.; 26 cm

The Peptide Alkaloid Anachelin: NMR Spectroscopic Evidence for ?-Turn Formation in Aqueous Solution

Anachelin, a complex secondary metabolite isolated from Anabaena cylindrica, possesses an unusual structure combining polyketide, peptide and alkaloid building blocks. This natural product was postulated to act as siderophore with catecholate and salicylate groups for putative iron binding with the three-dimensional solution structure of anachelin remaining unknown. In this preliminary communication, the conformation of anachelin in aqueous solution is investigated. ROESY experiments revealed several interresidual NOEs characteristic of a compact, folded structure. A ? -turn type structure of the central tripeptide sequence L-Thr-D-Ser-L-Ser structure involving D-Ser at position (i+1) and L-Ser at position (i+2) would be in agreement with the observed experimental data. In particular, this conformation of the free ligand would align the putative metal binding groups (structural preorganization) and thus lower the free energy for Fe binding. As it is highly unusual to see such a small tripeptide fragment folding into a compact structure, it appears reasonable to assume that both the cationic tetrahydroquinolinium ring as well as the trihydroxylated ?-amino acid contribute to the stabilization of the folded structure