Mu-conotoxin: Synthesis and Acting on Ion Channels and Transporters

General Description

The synthesis of Mu-conotoxins, bioactive peptides from marine cone snail venom with therapeutic potential, involves various methods like solid-phase peptide synthesis, native chemical ligation, and recombinant production. SPPS, utilizing Fmoc and Boc chemistry, allows for rapid and automated production, enabling structural modifications and incorporation of unnatural amino acids. For complex sequences, native chemical ligation is employed, while recombinaant production in heterologous systems is used for larger Mu-conotoxins. These methods facilitate the study of structure-activity relationships. Mu-conotoxins act on ion channels, particularly voltage-gated calcium channels, showing promise in treating chronic pain. Research focuses on developing second-generation Mu-conotoxins with improved efficacy and selectivity, considering structural variations from different species. Understanding these mechanisms is crucial for advancing pain management therapies.

Figure 1. Mu-conotoxin

Synthesis

Mu-conotoxins are bioactive peptides found in the venom of marine cone snails, with potential therapeutic applications due to their diverse biological activities. One common method for synthesizing Mu-conotoxins is through solid-phase peptide synthesis (SPPS), specifically using Fmoc and Boc chemistry. Fmoc-SPPS is favored for its simplicity in laboratory setup, while Boc-SPPS is utilized for challenging sequences or strategies incompatible with Fmoc chemistry. SPPS offers rapid and automated production of Mu-conotoxins, enabling the incorporation of unnatural amino acids, post-translational modifications (PTMs), imaging tags, and structural modifications like backbone cyclization. It also allows for the addition of fatty acids or PEG units to enhance bioavailability. In addition to SPPS, native chemical ligation can be employed for complex sequences and combinatorial studies. For larger Mu-conotoxins with multiple disulfide bonds or library screening, recombinant production in heterologous expression systems like Escherichia coli and yeast is common. This approach facilitates isotopic labeling for NMR studies and has been optimized for specific Mu-conotoxin types like α-TxIB. While Fmoc-SPPS and oxidative folding are primary methods for Mu-conotoxin synthesis, directed folding approaches using thiol-protecting groups like S-Acm and innovative strategies such as selenocysteine/cysteine combinations have emerged to simplify folding processes and enable the production of complex Mu-conotoxin structures. Ongoing advancements in folding reagents, solubility tags, and cyclization techniques contribute to the evolving landscape of Mu-conotoxin synthesis and structure-activity relationship studies. ¹

Acting on Ion Channels and Transporters

Conotoxins are bioactive peptides found in the venom of marine cone snails, with diverse biological activities that make them attractive for therapeutic applications. One significant area of research involves conotoxins acting on ion channels and transporters, particularly voltage-gated calcium channels (VGCCs), which play a crucial role in pain transmission. Notably, certain Mu-conotoxins have demonstrated selectivity as VGCC antagonists, showing promise in treating chronic pain conditions such as neuropathic pain. Among the Mu-conotoxins, ω-MVIIA (Prialt) has been a successful drug for severe chronic pain unresponsive to opioids, although its therapeutic index is limited by neurological and psychiatric side effects. To address this, efforts have been made to discover second-generation Mu-conotoxins with improved efficacy and reduced side effects. Research has focused on designing Mu-conotoxins with better selectivity and lower toxicity, aiming to enhance their therapeutic potential. While Mu-conotoxins from fish-hunting cone snails have been extensively studied, recent discoveries of mammalian active Mu-conotoxins from worm-hunting species, such as MoVIA and MoVIB, have provided new insights. These peptides exhibit different structural features, with arginine at position 13 playing a crucial role in their activity compared to tyrosine found in fish-hunting conotoxins. This discovery highlights the importance of understanding the structural requirements for high-affinity interactions of Mu-conotoxins with VGCCs, shedding light on potential variations in bioactivity based on the source species. Despite the challenges in discovering novel Mu-conotoxins, ongoing research aims to explore new sources and optimize peptide structures for enhanced therapeutic benefits. Understanding the mechanisms of action of conotoxins on ion channels and transporters remains a vital area of investigation for the development of novel pain management therapies. ²

Reference

1. Jin AH, Muttenthaler M, Dutertre S, et al. Conotoxins: Chemistry and Biology. Chem Rev. 2019;119(21):11510-11549.

2. Sanchez-Campos N, Bernaldez-Sarabia J, Licea-Navarro AF. Conotoxin Patenting Trends in Academia and Industry. Mar Drugs. 2022;20(8):531.