Biology subjects

Koehnke, J.

Publications and source records attributed to Koehnke, J..

5 recordsLinked to original sources

bioRxiv2026

Cryo-EM Structure of a Triazole alpha-Conotoxin GI Mimetic Bound to the Muscle-Type Nicotinic Acetylcholine Receptor

Disulfide-rich peptides possess exceptional potency and selectivity but are often limited by the instability and synthetic challenges associated with native disulfide bonds. Here, we report the design, synthesis, pharmacological evaluation, and structural characterisation of triazole-based peptidomimetics of the -GI conotoxin, a selective antagonist of the muscle-type nicotinic acetylcholine receptor (nAChR). A series of 1,4- and 1,5-disubstituted triazole analogues were prepared entirely on resin using CuAAC and RuAAC chemistry to replace the native Cys3/13 disulfide bridge. Functional evaluation against human muscle nAChRs revealed that 1,5-triazole analogues retained low-nanomolar potency, with the lead mimetic exhibiting activity comparable to native -GI. Cryo-electron microscopy of the lead compound bound to the muscle-type nAChR provided the first structure of a disulfide-isostere peptidomimetic in complex with a membrane receptor. The structure demonstrates that the 1,5-triazole reproduces the native peptide fold with high fidelity while contributing receptor-facing interactions not available to the native disulfide bridge. Molecular dynamics simulations further revealed conserved hydration networks and similar conformational sampling between the native peptide and lead mimetic. Together, these findings establish triazoles as effective disulfide surrogates and provide a structural framework for the rational design of stabilised conotoxin therapeutics.

biochemistry↗

bioRxiv2026

Acyl amides derived from a bacterial symbiont control development of its nematode host

Symbiotic bacteria frequently regulate host development through small-molecule signals. In the entomopathogenic Steinernema nematode - Xenorhabdus bacterium symbiosis, which is widely used in biological pest control, the signals that trigger nematode development have remained unknown. Using a phenotypic screen of Xenorhabdus mutants, we identified bacterial acyl amides, which we named stripteamides, as signals required for efficient recovery of Steinernema infective juveniles. Stripteamides are synthesized from phenylethylamine and activated fatty acid substrates by StaS, a previously uncharacterized amide synthase. Mechanistic and structural analyses indicate that StaS evolved from the initiation module of a nonribosomal peptide synthetase (NRPS) and was repurposed to generate signaling metabolites for host development. Stripteamide signaling is conserved across Xenorhabdus species and operates in different Steinernema hosts. These findings reveal a new function for widespread bacterial acyl amides that previously have been shown as cytotoxic and affecting bacterial quorum sensing, highlighting the context dependence of microbial natural product language.

microbiology↗

bioRxiv2026

Structures of muscle-type nicotinic acetylcholine receptor with α-conotoxins reveal determinants of receptor-subtype specificity

-Conotoxins (-CTX) are disulfide-rich peptide antagonists with exceptional potency and subtype selectivity across nicotinic acetylcholine receptors (nAChRs), making them promising leads for therapeutic development. The molecular basis of their specificity has remained unresolved for decades, limiting rational drug design. Here, we present the first high-resolution cryo-EM structures of full-length muscle-type nAChR bound to three distinct -CTXs, revealing their precise binding modes at both acetylcholine binding sites. Our integrated approach, combining structural biology, pharmacological profiling, and computational hydration mapping, uncovers conserved pharmacophore features, water-mediated interactions, and subunit-specific determinants that govern potency and selectivity. These findings provide a long-sought molecular framework for -conotoxin recognition and inhibition, addressing a critical gap required to realise the full potential of conotoxins as lead compounds in drug discovery.

molecular biology↗

bioRxiv2024

A fucose-binding superlectin from Enterobacter cloacae with high Lewis and ABO blood group antigen specificity

Bacteria frequently employ carbohydrate-binding proteins, so-called lectins, to colonize and persist in a host. Thus, bacterial lectins are attractive targets for the development of new antiinfectives. To find new potential targets for antiinfectives against pathogenic bacteria, we searched for homologs of Pseudomonas aeruginosa lectins and identified homologs of LecA in Enterobacter species. Here, we recombinantly produced and biophysically characterized a homolog that comprises one LecA domain and one additional novel protein domain. This protein was termed Enterobacter cloacae lectin A (EclA) and found to bind L-fucose. Glycan array analysis revealed a high specificity for the LewisA antigen and the type II H-antigen (blood group O) for EclA, while related antigens LewisX, Y, and B as well as blood group A or B were not bound. We developed a competitive binding assay to quantify blood group antigen binding specificity in solution. Finally, the crystal structure of EclA could be solved in complex with methyl -L-selenofucoside. It revealed the unexpected binding of the carbohydrate ligand to the second domain, which comprises a novel fold that dimerizes via strand-swapping resulting in an intertwined beta sheet.

microbiology↗

bioRxiv2020

Biosynthesis of cittilins, unusual ribosomally synthesized and post-translationally modified peptides from Myxococcus xanthus

Cittilins are secondary metabolites from myxobacteria comprised of three L-tyrosines and one L-isoleucine forming a bicyclic tetrapeptide scaffold with biaryl and aryl-oxygen-aryl ether bonds. Here we reveal that cittilins belong to the ribosomally synthesized and post-translationally modified peptide (RiPP) family of natural products, for which only the crocagins have been reported from myxobacteria. A 27 amino acid precursor peptide harbors a C-terminal four amino acid core peptide, which is enzymatically modified and finally exported to yield cittilins. The small biosynthetic gene cluster responsible for cittilin biosynthesis also encodes a cytochrome P450 enzyme and a methyltransferase, whereas a gene encoding a prolyl endopeptidase for the cleavage of the precursor peptide is located outside of the cittilin biosynthetic gene cluster. We confirm the roles of the biosynthetic genes responsible for the formation of cittilins using targeted gene inactivation and heterologous expression in Streptomyces. We also report first steps towards the biochemical characterization of the proposed biosynthetic pathway in vitro. An investigation of the cellular uptake properties of cittilin A connected it to a potential biological function as an inhibitor of the prokaryotic carbon storage regulator A (CsrA). O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/114512v1_ufig1.gif" ALT="Figure 1"> View larger version (15K): org.highwire.dtl.DTLVardef@11da6b5org.highwire.dtl.DTLVardef@1abc508org.highwire.dtl.DTLVardef@14bb22org.highwire.dtl.DTLVardef@109cedd_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗