Liposomal Circular Dichroism (L-CD) of Arenoyl Derivatives of Sphingolipids. Amplification of Cotton Effects in Ordered Lipid Bilayers.

Liposomal circular dichroism (L-CD) of acyclic amino alcohols exhibit amplification of Cotton effects when measured in highly uniform, unilamellar liposomes. The effect is likely due to intermolecular associations-H-aggregates-that self-assemble spontaneously within the lipid bilayer, and persists over long time scales. L-CD spectra of N,O,O'-tri-(6'methoxy-2'-naphthoyl)-d-erythro-sphingosine, or the corresponding dihydro-derivative (sphinganine), shows ~10-fold amplification of magnitudes of Cotton effects over conventional CD spectra recorded in isotropic solution

Liposomal Circular Dichroism (L-CD) of Arenoyl Derivatives of Sphingolipids. Amplification of Cotton Effects in Ordered Lipid Bilayers

Liposomal circular dichroism (L-CD) of acyclic amino alcohols exhibit amplification of Cotton effects when measured in highly uniform, unilamellar liposomes. The effect is likely due to intermolecular associations—H-aggregates—that self-assemble spontaneously within the lipid bilayer, and persists over long time scales. L-CD spectra of N,O,O′-tri-(6′methoxy-2′-naphthoyl)-d-erythro-sphingosine, or the corresponding dihydro-derivative (sphinganine), shows ~10-fold amplification of magnitudes of Cotton effects over conventional CD spectra recorded in isotropic solution

An Orthogonal D 2 O-Based Induction System that Provides Insights into d -Amino Acid Pattern Formation by Radical S-Adenosylmethionine Peptide Epimerases

International audienceRadical S-adenosyl methionine peptide epimerases (RSPEs) are an enzyme family that accomplishes regiospecific and irreversible introduction of multiple d-configured residues into ribosomally encoded peptides. Collectively, RSPEs can generate diverse epimerization patterns in a wide range of substrates. Previously, the lack of rapid methods to localize epimerized residues has impeded efforts to investigate the function and applicative potential of RSPEs. An efficient mass spectrometry-based assay is introduced that permits characterization of products generated in E. coli. Applying this to a range of non-natural peptide-epimerase combinations, it is shown that the d-amino acid pattern is largely but not exclusively dictated by the core peptide sequence, while the epimerization order is dependent on the enzyme-leader pair. RSPEs were found to be highly promiscuous, which allowed for modular introduction of peptide segments with defined patterns

Structures and Solution Conformational Dynamics of Stylissamides G and H from the Bahamian Sponge <i>Stylissa caribica</i>

Two new peptides, stylissamides G and H, were isolated from extracts of a sample of <i>Stylissa caribica</i> collected in deep waters of the Caribbean Sea. A single sample of <i>S. caribica</i> among a collection of 10 samples that were examined by LC-MS appeared to be a different chemotype from the others in that it lacked the familiar pyrrole-2-aminoimidazole alkaloids, stevensine and oroidin, and contained peptides of the stylissamide class. The structures of the title compounds were solved by integrated analysis of the MS and NMR spectra and chemical degradation. The solution conformation of stylissamide G was briefly examined by electronic circular dichroism and temperature-dependent ¹H NMR chemical shifts of amide NH signals, which supported a conformationally rigid macrocycle

Toblerols, Cyclopropanol-Containing Modulators of Methylobacterial Antibiosis Generated by an Unusual Polyketide Synthase

ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

Symplocin A, a Linear Peptide from the Bahamian Cyanobacterium <i>Symploca</i> sp. Configurational Analysis of <i>N</i>,<i>N</i>-Dimethylamino Acids by Chiral-Phase HPLC of Naphthacyl Esters

The absolute stereostructures of the components of symplocin A (<b>3</b>), a new <i>N</i>,<i>N</i>-dimethyl-terminated peptide from the Bahamian cyanobacterium <i>Symploca</i> sp., were assigned from spectroscopic analysis, including MS, 2D NMR, and Marfey’s analysis. The complete absolute configuration of symplocin A, including the unexpected d-configurations of the terminal <i>N</i>,<i>N</i>-dimethylisoleucine and valic acid residues, was assigned by chiral-phase HPLC of the corresponding 2-naphthacyl esters, a highly sensitive, complementary strategy for assignment of N-blocked peptide residues where Marfey’s method is ineffectual or other methods fall short. Symplocin A exhibited potent activity as an inhibitor of cathepsin E (IC₅₀ 300 pM)