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The application of selenocysteine in a supported phase method to direct native folding and produce [alpha]-conotoxins efficiently with improved biophysical properties is reported. The results obtained provide insight into the development of more stable and potent nicotinic antagonists suitable for new drug therapies, and highlight the application of selenocysteine technology more broadly to disulfide-bonded peptides and proteins.

The article describes conotoxin diversity at the sequence and structural level and offers critical information for chemists wanting to engineering conotoxins. Topics discussed include the idea that the conotoxin gene family is one of the fastest evolving gene families of the animal kingdom and studies on truncation muta-genesis conotoxins undertaken to define the relationship between loop size and conotoxin structure and function.

Disulfide bond engineering is an important approach to improve the metabolic half-life of cysteine-containing peptides. Eleven analogues of oxytocin were synthesized including disulfide bond replacements by thioether, selenylsulfide, diselenide, and ditelluride bridges, and their stabilities in human plasma and activity at the human oxytocin receptor were assessed. The cystathionine (Ki = 1.5 nM, and EC50 = 32 nM), selenylsulfide (Ki = 0.29/0.72 nM, and EC50 = 2.6/154 nM), diselenide (Ki = 11.8 nM, and EC50 = 18 nM), and ditelluride analogues (Ki = 7.6 nM, and EC50 = 27.3 nM) retained considerable affinity and functional potency as compared to oxytocin (Ki = 0.79 nM, and EC50 = 15 nM), while shortening the disulfide bridge abolished binding and functional activity. The mimetics showed a 1.5−3-fold enhancement of plasma stability as compared to oxytocin (t1/2 = 12 h). By contrast, the all-d-oxytocin and head to tail cyclic oxytocin analogues, while significantly more stable with half-lives greater than 48 h, had little or no detectable binding or functional activity. [ABSTRACT FROM AUTHOR]

α-Conotoxins are tightly folded miniproteins that antagonize nicotinic acetyicholine receptors (nAChR) with high specificity for diverse subtypes. Here we report the use of selenocysteine in a supported phase method to direct native folding and produce α-conotoxins efficiently with improved biophysical properties. By replacing complementary cysteine pairs with selenocysteine pairs on an amphiphilic resin, we were able to chemically direct all five structural subclasses of α-conotoxins exclusively into their native folds. X-ray analysis at 1.4 Å resolution of α-selenoconotoxin PnlA confirmed the isosteric character of the diselenide bond and the integrity of the a-conotoxin fold. The α-selenoconotoxins exhibited similar or improved potency at rat diaphragm muscle and α3β4, α7, and α1β1δγ nAChRs expressed in Xenopus oocytes plus improved disulfide bond scrambling stability in plasma. Together, these results underpin the development of more stable and potent nicotinic antagonists suitable for new drug therapies, and highlight the application of selenocysteine technology more broadly to disulfide-bonded peptides and proteins. [ABSTRACT FROM AUTHOR]

Visceral leishmaniasis is a neglected tropical disease with the highest mortality among different forms of leishmaniasis manifestation in humans. The disease is caused by the parasitic protists Leishmania donovani and Leishmania infantum , and treatments remain unsuitable due to high costs, complicated administration, lack of efficacy, variable patient susceptibility, toxic side effects, and rising parasitic resistance. Herein, we report a structure-activity relationship (SAR) exploration of the diacyl-hydrazide scaffold identified to have antiparasitic activity from a high-throughput screen against L. donovani , Trypanosoma cruzi , and Trypanosoma brucei . This SAR study revealed new structural insights into this scaffold related to bioactivity resulting in a new series of lead compounds with nanomolar activity against L. donovani and no toxicity against human THP-1 macrophages. These optimized diacyl-hydrazide compounds set the stage for future drug development and hold promise for a new treatment avenue for visceral leishmaniasis., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

TFF3 regulates essential gastro- and neuroprotective functions, but its molecular mode of action remains poorly understood. Synthetic intractability and lack of reliable bioassays and validated receptors are bottlenecks for mechanistic and structure-activity relationship studies. Here, we report the chemical synthesis of TFF3 and its homodimer via native chemical ligation followed by oxidative folding. Correct folding was confirmed by NMR and circular dichroism, and TFF3 and its homodimer were not cytotoxic or hemolytic. TFF3, its homodimer, and the trefoil domain (TFF3 10-50 ) were susceptible to gastrointestinal degradation, revealing a gut-stable metabolite (TFF3 7-54 ; t 1/2 > 24 h) that retained its trefoil structure and antiapoptotic bioactivity. We tried to validate the putative TFF3 receptors CXCR4 and LINGO2, but neither TFF3 nor its homodimer displayed any activity up to 10 μM. The discovery of a gut-stable bioactive metabolite and reliable synthetic accessibility to TFF3 and its analogues are cornerstones for future molecular probe development and structure-activity relationship studies.

High susceptibility to proteolytic degradation in the gastrointestinal tract limits the therapeutic application of peptide drugs in gastrointestinal disorders. Linaclotide is an orally administered peptide drug for the treatment of irritable bowel syndrome with constipation (IBS-C) and abdominal pain. Linaclotide is however degraded in the intestinal environment within 1 h, and improvements in gastrointestinal stability might enhance its therapeutic application. We therefore designed and synthesized a series of linaclotide analogues employing a variety of strategic modifications and evaluated their gastrointestinal stability and pharmacological activity at its target receptor guanylate cyclase-C. All analogues had substantial improvements in gastrointestinal half-lives (>8 h vs linaclotide 48 min), and most remained active at low nanomolar concentrations. This work highlights strategic approaches for the development of gut-stable peptides toward the next generation of orally administered peptide drugs for the treatment of gastrointestinal disorders.