Poly-adenosine diphosphate ribose (PAR) is a branched biopolymer that occurs as a result of post-translational modification of proteins. In 1981 Miwa et al. determined the structure of... Show morePoly-adenosine diphosphate ribose (PAR) is a branched biopolymer that occurs as a result of post-translational modification of proteins. In 1981 Miwa et al. determined the structure of enzymatically prepared branched PAR. We present the first synthesis of the same branched PAR fragment and have shown by NMR that the structure proposed by Miwa is correct. Show less
A study of the kinetics of liquid phase hydrogenation of nitrobenzene, 4-nitrotoluene, 4-nitroaniline and 2-chloro-4-nitroaniline on supported palladium catalyst in aqueous solutions of 2-propanol... Show moreA study of the kinetics of liquid phase hydrogenation of nitrobenzene, 4-nitrotoluene, 4-nitroaniline and 2-chloro-4-nitroaniline on supported palladium catalyst in aqueous solutions of 2-propanol of different composition was carried out. The influence of the substituent on the value of the total amount of hydrogen absorbed during the reaction and the kinetics of the hydrogenation of substituted nitrobenzenes was discussed. It was found out that the reaction selectivity to 2-chloro-1,4-phenylenediamine decreases due to by-reaction dehalogenation. The degree of dehalogenation depends on the composition of solvent and may be approximately estimated by the values of the absorbed hydrogen volume during the reaction. Also, the presence of the donor-acceptor substituents is capable of exerting influence on the reaction rate of hydrogenation of the nitro compound. Show less
Mono-ADP-ribosylation is a dynamic posttranslational modification (PTM) with important roles in signaling. Mammalian proteins that recognize or hydrolyze mono-ADP-ribosylated proteins have been... Show moreMono-ADP-ribosylation is a dynamic posttranslational modification (PTM) with important roles in signaling. Mammalian proteins that recognize or hydrolyze mono-ADP-ribosylated proteins have been described. We report the synthesis of ADP-ribosylated peptides from the proteins histone H2B, RhoA and, HNP-1. An innovative procedure was applied that makes use of pre-phosphorylated amino acid building blocks. Binding assays revealed that the macrodomains of human MacroD2 and TARG1 exhibit distinct specificities for the different ADP-ribosylated peptides, thus showing that the sequence surrounding ADP-ribosylated residues affects the substrate selectivity of macrodomains. Show less
Chirally pure R- and S-epimers of TLR2 ligand Pam3CysSK4 were prepared and separately conjugated to an OVA model epitope, in which lysine was replaced by azidonorleucine. The azide function in the... Show moreChirally pure R- and S-epimers of TLR2 ligand Pam3CysSK4 were prepared and separately conjugated to an OVA model epitope, in which lysine was replaced by azidonorleucine. The azide function in the conjugate permitted labelling with different fluorophores by use of strain-promoted 3+2 cycloaddition. The R-epimer of the labelled conjugates induced TLR2-dependent DC maturation, while S-epimer proved to be inactive. Combining the lipophilicity of Pam3CysSK4 ligand with fluorophores influenced the solubility of the resulting conjugates in an unpredictable way and only the conjugates labelled with Cy-5 were suitable for confocal fluorescence microscopy experiments. It was shown that both epimers of the Cy-5 labelled lipopeptides were internalized equally well, indicating TLR2-independent cellular uptake. The presented results demonstrate the usefulness of strain-promoted azide-alkyne cycloaddition in the labelling of highly lipophilic lipopeptides without disturbing the in vitro activity of these conjugates with respect to activation of TLR-2. Show less
This work reports the development of highly potent and selective inhibitors of the β5c catalytic activity of human constitutive proteasomes. The work describes the design principles, large... Show moreThis work reports the development of highly potent and selective inhibitors of the β5c catalytic activity of human constitutive proteasomes. The work describes the design principles, large hydrophobic P3 residue and small hydrophobic P1 residue, that led to the synthesis of a panel of peptide epoxyketones; their evaluation and the selection of the most promising compounds for further analyses. Structure-activity relationships detail how in a logical order the β1c/i, β2c/i, and β5i activities became resistant to inhibition as compounds were diversified stepwise. The most effective compounds were obtained as a mixture of cis- and trans-biscyclohexyl isomers, and enantioselective synthesis resolved this issue. Studies on yeast proteasome structures complexed with some of the compounds provide a rationale for the potency and specificity. Substitution of the N-terminus in the most potent compound for a more soluble equivalent led to a cell-permeable molecule that selectively and efficiently blocks β5c in cells expressing both constitutive proteasomes and immunoproteasomes. Show less
Hashemi Shabestari, M.; Meeuwenoord, N.J.; Filippov, D.V.; Huber, M.I. 2016
The amyloid β (A β) peptide is important in the context of Alzheimer's disease, since it is one of the major components of the fibrils that constitute amyloid plaques. Agents that can influence... Show moreThe amyloid β (A β) peptide is important in the context of Alzheimer's disease, since it is one of the major components of the fibrils that constitute amyloid plaques. Agents that can influence fibril formation are important, and of those, membrane mimics are particularly relevant, because the hydrophobic part of A β suggests a possible membrane activity of the peptide. We employed spin-label EPR to investigate the aggregation process of A β1-40 in the presence of the sodium dodecyl sulfate (SDS) detergent as a membrane-mimicking agent. In this work, the effect of SDS on A β is studied using two positions of spin label, the N-terminus and position 26. By comparing the two label positions, the effect of local mobility of the spin label is eliminated, revealing A β aggregation in the SDS concentration regime below the critical micelle concentration (CMC). We demonstrate that, at low SDS concentrations, the N-terminus of A β participates in the solubilization, most likely by being located at the particle-water interface. At higher SDS concentrations, an SDS-solubilized state that is a precursor to the one A β/micelle state above the CMC of SDS prevails. We propose that A β is membrane active and that aggregates include SDS. This study reveals the unique potential of EPR in studying A β aggregation in the presence of detergent. Show less
