Rapid and Selective Chemical Editing of Ribosomally Synthesized and Post-Translationally Modified Peptides (RiPPs) via CuII -Catalyzed β-Borylation of Dehydroamino Acids

We report the fast and selective chemical editing of ribosomally synthesized and post-translationally modified peptides (RiPPs) by β-borylation of dehydroalanine (Dha) residues. The thiopeptide thiostrepton was modified efficiently using CuII -catalysis under mild conditions and 1D/2D NMR of the purified product showed site-selective borylation of the terminal Dha residues. Using similar conditions, the thiopeptide nosiheptide, lanthipeptide nisin Z, and protein SUMO_G98Dha were also modified efficiently. Borylated thiostrepton showed an up to 84-fold increase in water solubility, and minimum inhibitory concentration (MIC) assays showed that antimicrobial activity was maintained in thiostrepton and nosiheptide. The introduced boronic-acid functionalities were shown to be valuable handles for chemical mutagenesis and in a reversible click reaction with triols for the pH-controlled labeling of RiPPs.

Cu(II)-Catalysed β-silylation of dehydroalanine residues in peptides and proteins

We report the efficient and selective Cu(ii)-catalysed β-silylation of naturally occurring dehydroalanine (Dha) residues in various ribosomally synthesized and post-translationally modified peptides (RiPPs). The method is also applicable to proteins, as was shown by the modification of a Dha residue that was chemically introduced into Small Ubiquitin-like Modifier (SUMO).

Characterization of two relacidines belonging to a novel class of circular lipopeptides that act against Gram-negative bacterial pathogens

The development of sustainable agriculture and the increasing antibiotic resistance of human pathogens call for novel antimicrobial compounds. Here, we describe the extraction and characterization of a class of cationic circular lipopeptides, for which we propose the name relacidines, from the soil bacterium Brevibacillus laterosporus MG64. Relacidines are composed of a fatty acid side chain (4‐methylhexanoic acid) and 13 amino acid residues. A lactone ring is formed by the last five amino acid residues and three positively charged ornithines are located in the linear fragment. Relacidines selectively combat Gram‐negative pathogens, including phytopathogens and human pathogens. Further investigation of the mode of action revealed that relacidine B binds to the lipopolysaccharides but does not form pores in the cell membrane. We also provide proof to show that relacidine B does not affect the biosynthesis of the cell wall and RNA. Instead, it affects the oxidative phosphorylation process of cells and diminishes the biosynthesis of ATP. Transcription of relacidines is induced by plant pathogens, which strengthens the potential of B. laterosporus MG64 to be used as a biocontrol agent. Thus, we identified a new group of potent antibiotic compounds for combating Gram‐negative pathogens of plants or animals.

A Trifunctional Linker for Palmitoylation and Peptide and Protein Localization in Biological Membranes

Attachment of lipophilic groups is an important post-translational modification of proteins, which involves the coupling of one or more anchors such as fatty acids, isoprenoids, phospholipids, or glycosylphosphatidyl inositols. To study its impact on the membrane partitioning of hydrophobic peptides or proteins, we designed a tyrosine-based trifunctional linker. The linker allows the facile incorporation of two different functionalities at a cysteine residue in a single step. We determined the effect of the lipid modification on the membrane partitioning of the synthetic α-helical model peptide WALP with or without here and in all cases below; palmitoyl groups in giant unilamellar vesicles that contain a liquid-ordered (Lo ) and liquid-disordered (Ld ) phase. Introduction of two palmitoyl groups did not alter the localization of the membrane peptides, nor did the membrane thickness or lipid composition. In all cases, the peptide was retained in the Ld phase. These data demonstrate that the Lo domain in model membranes is highly unfavorable for a single membrane-spanning peptide.

Selective Modification of Ribosomally Synthesized and Post-Translationally Modified Peptides (RiPPs) through Diels-Alder Cycloadditions on Dehydroalanine Residues

We report the late‐stage chemical modification of ribosomally synthesized and post‐translationally modified peptides (RIPPs) by Diels–Alder cycloadditions to naturally occurring dehydroalanines. The tail region of the thiopeptide thiostrepton could be modified selectively and efficiently under microwave heating and transition‐metal‐free conditions. The Diels–Alder adducts were isolated and the different site‐ and endo/exo isomers were identified by 1D/2D ¹H NMR. Via efficient modification of the thiopeptide nosiheptide and the lanthipeptide nisin Z the generality of the method was established. Minimum inhibitory concentration (MIC) assays of the purified thiostrepton Diels–Alder products against thiostrepton‐susceptible strains displayed high activities comparable to that of native thiostrepton. These Diels–Alder products were also subjected successfully to inverse‐electron‐demand Diels–Alder reactions with a variety of functionalized tetrazines, demonstrating the utility of this method for labeling of RiPPs.