1,720,962 research outputs found
Azide reduction during peptide cleavage from solid support—the choice of thioscavenger?
No full textPeptide azides acquired growing impact because of application in bioconjugation via 'click chemistry' or Staudinger ligation. Furthermore, there are many methods established in organic synthesis addressing the reduction of azides to amines, but no observation of a reductive transformation of peptide azides during SPPS cleavage was yet reported. In the present study, the reduction of peptide azides during SPPS cleavage was investigated depending on the choice of thioscavenger, reacting as reductive species. First observed for short PNA/peptide conjugates the occurring extensive side reaction was also validated for one of the applied azide amino acid building blocks and was further investigated by applying different cleavage cocktails to a series of peptides varying in hydrophobicity and position of the azide moiety in the oligomer sequence. Copyright (C) 2009 European Peptide Society and John Wiley & Sons, Ltd.Deutsche Forschungsgemeinschaft [SFB 803
Membrane‐Associated Nucleobase‐Functionalized β‐Peptides (β‐PNAs) Affecting Membrane Support and Lipid Composition
No full textProtein-membrane interactions are essential to maintain membrane integrity and control membrane morphology and composition. Cytoskeletal proteins in particular are known to interact to a high degree with lipid bilayers and to line the cytoplasmic side of the plasma membrane with an extensive network structure. In order to gain a better mechanistical understanding of the protein-membrane interplay and possible membrane signaling, we started to develop a model system based on β-peptide nucleic acids (β-PNAs). These β-peptides are known to form stable hydrogen-bonded aggregates due to their helical secondary structure, which serve to pre-organize the attached nucleobases. After optimization of the β-PNA solid-phase peptide synthesis and validation of helix formation, the ability of the novel β-PNAs to dimerize and interact with lipid bilayers was investigated by both fluorescence and circular dichroism spectroscopy. It was shown that duplex formation occurs rapidly and with high specificity and could also be detected on the surfaces of the lipid bilayers. Hereby, the potential of a β-PNA-based peptide system to mimic membrane-associated protein networks could be demonstrated
N -Hydroxy pipecolic acid methyl ester is involved in Arabidopsis immunity
No full textAbstract
The biosynthesis of N-hydroxy pipecolic acid (NHP) has been intensively studied, though knowledge on its metabolic turnover is still scarce. To close this gap, we discovered three novel metabolites via metabolite fingerprinting in Arabidopsis thaliana leaves after Pseudomonas infection and UV-C treatment. Exact mass information and fragmentation by tandem mass spectrometry (MS/MS) suggest a methylated derivative of NHP (MeNHP), an NHP-OGlc-hexosyl conjugate (NHP-OGlc-Hex), and an additional NHP-OGlc-derivative. All three compounds were formed in wild-type leaves but were not present in the NHP-deficient mutant fmo1-1. The identification of these novel NHP-based molecules was possible by a dual-infiltration experiment using a mixture of authentic NHP and D9-NHP standards for leaf infiltration followed by UV-C treatment. Interestingly, the signal intensity of MeNHP and other NHP-derived metabolites increased in ugt76b1-1 mutant plants. For MeNHP, we unequivocally determined the site of methylation at the carboxylic acid moiety. MeNHP application by leaf infiltration leads to the detection of a MeNHP-OGlc as well as NHP, suggesting MeNHP hydrolysis to NHP. This is in line with the observation that MeNHP infiltration is able to rescue the fmo1-1 susceptible phenotype against Hyaloperonospora arabidopsidis Noco 2. Together, these data suggest MeNHP as an additional storage or transport form of NHP
Molecular Recognition at the Membrane-Water Interface: Controlling Integral Peptide Helices by Off-Membrane Nucleobase Pairing
No full textThe aggregation and organization of membrane proteins and transmembrane peptides is related to the interacting molecular species itself and strongly depends on the lipid environment. Because of the complexity and dynamics of these interactions, they are often hardly traceable and nearly impossible to predict. For this reason, peptide model systems are a valuable tool in studying membrane associated processes since they are synthetically accessible and can be readily modified. To control and study the aggregation of peptide transmembrane domains (TMDs) the interacting interfaces of the TMDs themselves can be altered. A second less extensively studied approach targets the TMD assembly by using interaction and recognition of domains at the membrane outside as frequently found in the membrane protein interplay and protein assembly. In the present study, double helical transmembrane domains were designed and synthesized on the basis of a recently reported D,L-alternating peptide pore motif derived from gramicidin A. The highly hydrophobic and aromatic transmembrane peptide was covalently functionalized with a short peptide nucleic acid (PNA) used as specific outer-membrane recognition unit. The PNA sequences were chosen with high polarity to ensure localization within the aqueous phase. To estimate the impact of the membrane adjacent recognition on the TMD assembly by Forster resonance energy transfer (FRET), fluorescence probes were covalently attached to the side chains of the membrane spanning peptide helices. Dimerization of the TMD-peptide/PNA conjugates within unilamellar lipid vesicles was observed. The dimer/monomer ratio of TMDs can be controlled by temperature variation
A Novel Heavy‐Atom Label for Side‐Specific Peptide Iodination: Synthesis, Membrane Incorporation and X‐ray Reflectivity
No full textStructural parameters, such as conformation, orientation and penetration depth of membrane-bound peptides and proteins that may function as channels, pores or biocatalysts, are of persistent interest and have to be probed in the native fluid state of a membrane. X-ray scattering in combination with heavy-atom labeling is a powerful and highly appropriate method to reveal the position of a certain amino acid residue within a lipid bilayer with respect to the membrane normal axis up to a resolution of several Angstrom. Herein, we report the synthesis of a new iodine-labeled amino acid building block. This building block is intended for peptide incorporation to provide high intensities for electron density difference analysis of X-ray reflectivity data and improve the labeling potential for the lipid bilayer head-group and water region. The novel building block as well as the commercially available non-iodinated analogue, required for X-ray scattering, was implemented in a transmembrane peptide motif via manual solid-phase peptide synthesis (SPPS) following the fluorenylmethyloxycarbonyl (Fmoc)-strategy. The derived peptides were reconstituted in lipid vesicles as well as in highly aligned multilamellar lipid stacks and investigated via circular dichroism (CD) and X-ray reflectivity. Thereby, it has been revealed that the bulky iodine probe neither causes conformational change of the peptide structure nor lamellar disordering of the membrane complexes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Semi‐rigid nitroxide spin label for long‐range EPR distance measurements of lipid bilayer embedded β‐peptides.
Full text linkβ‐Peptides are an interesting new class of transmembrane model peptides based on their conformationally stable and well‐defined secondary structures. Herein, we present the synthesis of the paramagnetic β‐amino acid β3‐hTOPP (4‐(3,3,5,5‐tetramethyl‐2,6‐dioxo‐4‐oxylpiperazin‐1‐yl)‐d‐β3‐homophenylglycine) that enables investigations of β‐peptides by EPR spectroscopy. This amino acid adds to the so far sparse number of β‐peptide spin labels. Its performance was evaluated by investigating the helical turn of a 314‐helical transmembrane model β‐peptide. Nanometer distances between two incorporated β3‐hTOPP labels in different environments were measured using PELDOR/DEER (pulsed electron‐electron double resonance) spectroscopy. Due to the semi‐rigid conformational design, the label delivers reliable distances and sharp (one‐peak) distance distributions even in the lipid bilayer. The results indicate that the investigated β‐peptide folds into a 3.2514 helix and maintains this conformation in the lipid bilayer
N‐(sulfonio)sulfilimine reagents: Non‐oxidizing Sources of Electrophilic Nitrogen Atom for Skeletal Editing
No full textThe one‐pot synthesis of λ4‐dibenzothiophen‐5‐imino‐N‐dibenzothiophenium triflate (1) in multigram scale is reported. This compound reacts with Rh2(esp)2 (esp = α,α,α′,α′‐tetramethyl‐1,3‐benzenedipropionic acid) generating a Rh‐coordinated sulfonitrene species, which is able to transfer the electrophilic nitrene moiety to olefins. When indenes are used as substrates, isoquinolines are obtained in good yields. We assumed that after formation of the corresponding N‐sulfonio aziridine, a ring expansion occurs via selective C‐C bond cleavage and concomitant elimination of dibenzothiophene. Unexpectedly, a similar protocol transforms 1‐arylcyclobutenes into 1‐cyano‐1‐arylcyclopropanes. Our calculations indicate that aziridination is not favored in this case; instead, sulfilimine‐substituted cyclobutyl carbocations are initially formed, and these evolve to the isolated cyclopropanes via ring contraction. Both procedures are operationally simple, tolerate a range of functional groups, including oxidation‐sensitive alcohols and aldehydes, and enable the convenient preparation of valuable 15N‐labelled products. These results demonstrate the potential of 1 to provide alternative pathways for the selective transfer of N‐atoms in organic molecules
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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