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Ruthenium‐catalysed azide–alkyne cycloaddition (RuAAC) provides access to 1,5‐disubstituted 1,2,3‐triazole motifs in peptide engineering applications. However, investigation of this motif as a disulfide mimetic in cyclic peptides has been limited, and the structural consequences remain to be studied. We report synthetic strategies to install various triazole linkages into cyclic peptides through backbone cyclisation and RuAAC cross‐linking reactions. These linkages were evaluated in four serine protease inhibitors based on sunflower trypsin inhibitor‐1. NMR and X‐ray crystallography revealed exceptional consensus of bridging distance and backbone conformations (RMSD<0.5 Å) of the triazole linkages compared to the parent disulfide molecules. The triazole‐bridged peptides also displayed superior half‐lives in liver S9 stability assays compared to disulfide‐bridged peptides. This work establishes a foundation for the application of 1,5‐disubstituted 1,2,3‐triazoles as disulfide mimetics. [ABSTRACT FROM AUTHOR]

ABSTRACT The cyclotides are a family of small head-to-tail cyclic plant defense proteins. In addition to their cyclic backbone, cyclotides comprise three disulfide bonds in a knotted arrangement, resulting in a highly cross-braced structure that provides exceptional chemical and proteolytic stability. A number of bioactivities have been associated with cyclotides, including insecticidal, antimicrobial, anti-viral and cytotoxic, and these activities are related to an ability to target and disrupt biological membranes. Kalata B2 and to a lesser extent kalata B1, isolated from Oldenlandia affinis, self-associate to tetramers and octamers in aqueous buffers, and this oligomerization has been suggested to be relevant for their ability to form pores in membranes. Here we demonstrate by solution NMR spectroscopy analysis that the oligomerization of kalata B2 is concentration dependent and that it involves the packing of hydrophobic residues normally exposed on the surface of kalata B2 into a multimeric hydrophobic core. Interestingly, the hydrophobic surface that is 'quenched' has previously been shown to be responsible for the ability of kalata B2 to insert into membranes. Thus, it seems unlikely that the oligomers observed in aqueous solution are related to any multimeric state present in a membrane environment, and responsible for the formation of pores. The ability to self-associate might alternatively provide a mechanism for preventing self-toxicity when stored at high concentrations in intracellular compartments. © 2013 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 453-460, 2013. [ABSTRACT FROM AUTHOR]

Innentitelbild: Application and Structural Analysis of Triazole-Bridged Disulfide Mimetics in Cyclic Peptides (Angew. Keywords: disulfide mimetics; inhibitors; peptides; peptidomimetics; triazole bridges EN disulfide mimetics inhibitors peptides peptidomimetics triazole bridges 11258 11258 1 07/03/20 20200706 NES 200706 B 1,5-Disubstituierte 1,2,3-Triazole b können als Mimetika von Disulfidbindungen genutzt werden. Disulfide mimetics, inhibitors, peptides, peptidomimetics, triazole bridges. [Extracted from the article]

The θ-defensins are, to date, the only known ribosomally synthesized cyclic peptides in mammals, and they have promising antimicrobial bioactivities. The characteristic structural motif of the θ-defensins is the cyclic cystine ladder, comprising a cyclic peptide backbone and three parallel disulfide bonds. In contrast to the cyclic cystine knot, which characterizes the plant cyclotides, the cyclic cystine ladder has not been as well described as a structural motif. Here we report the solution structures and nuclear magnetic resonance relaxation properties in aqueous solution of three representative θ-defensins from different species. Our data suggest that the θ-defensins are more rigid and structurally defined than previously thought. In addition, all three θ-defensins were found to self-associate in aqueous solution in a concentration-dependent and reversible manner, a property that might have a role in their mechanism of action. The structural definition of the θ-defensins and the cyclic cystine ladder will help to guide exploitation of these molecules as structural frameworks for the design of peptide drugs. [ABSTRACT FROM AUTHOR]

Cyclic peptides are increasinglybeing recognized as valuable templatesfor drug discovery or design. To facilitate efforts in the structuralcharacterization of cyclic peptides, we explore the use of pulse-fieldgradient experiments as a convenient and noninvasive approach forcharacterizing their diffusion properties in solution. We presentdiffusion coefficient measurements of five cyclic peptides, includingdichC, SFTI-1, cVc1.1, kB1, and kB2. These peptides range in sizefrom six to 29 amino acids and have various therapeutically interestingactivities. We explore the use of internal standards, such as dioxaneand acetonitrile, to evaluate the hydrodynamic radius from the diffusioncoefficient, and show that 2,2-dimethyl-2-silapentane-5-sulfonic acid,a commonly used chemical shift reference, can be used as an internalstandard to avoid spectral overlap issues and simplify data analysis.The experimentally measured hydrodynamic radii correlate with increasingmolecular weight and in silicopredictions. We furtherapplied diffusion measurements to characterize the self-associationof kB2 and showed that it forms oligomers in a concentration-dependentmanner, which may be relevant to its mechanism of action. Diffusioncoefficient measurements appear to have broad utility in cyclic peptidestructural biology, allowing for the rapid characterization of theirmolecular shape in solution. [ABSTRACT FROM AUTHOR]

Small macrocyclic peptides are promising candidates for new anti-infective drugs. To date, such peptides have been poorly studied in the context of anti-virulence targets. Using phage display and a self-designed peptide library, we identified a cyclic heptapeptide that can bind the carbon storage regulator A (CsrA) from Yersinia pseudotuberculosis and displace bound RNA. This disulfide-bridged peptide, showed an IC50 value in the low micromolar range. Upon further characterization, cyclisation was found to be essential for its activity. To increase metabolic stability, a series of disulfide mimetics were designed and a redox-stable 1,4-disubstituted 1,2,3-triazole analogue displayed activity in the double-digit micromolar range. Further experiments revealed that this triazole peptidomimetic is also active against CsrA from Escherichia coli and RsmA from Pseudomonas aeruginosa. This study provides an ideal starting point for medicinal chemistry optimization of this macrocyclic peptide and might pave the way towards broad-acting virulence modulators. [Display omitted] • Screening of self-designed phage library yielded very short macrocyclic peptide hits. • Identification of single-digit micromolar CsrA-RNA interaction inhibitor. • Synthesis of Triazole peptide as redox stable disulfide mimic. • NMR derived solution structure + docking experiments. • Activity on CsrA/RsmA from several species holds promise for broader acting antivirulence agents against Gram-negatives. [ABSTRACT FROM AUTHOR]