Conotoxins are disulfide-rich peptides that were isolated from the venom of marine snails. Ziconotide (ω-conotoxin MVIIA) is an approved analgesic for the treatment of chronic pain. MVIIA is a highly selective voltage-gated calcium channel (CaV2.2) inhibitor. However, the need to inject it into the spinal canal and adverse effects limit its widespread use.
Cyclization could be a way to improve the pharmaceutical properties of conotoxins. Compared to linear forms, cyclic peptides are generally more stable. However, so far chemical synthesis alone has been unable to produce correctly folded backbone-cyclized analogues of MVIIA.
Thomas Durek, David J. Craik, The University of Queensland, Brisbane, Australia, and colleagues have used an asparaginyl endopeptidase (AEP)-mediated cyclization to generate backbone-cyclized analogues of MVIIA for the first time. AEPs cleave peptides C-terminally at asparagine (N) or aspartic acid (D) residues after recognition of a suitable motif. The team synthesized MVIIA analogues that incorporate a linker segment containing five to nine amino acid residues between the N-and C-termini using solid-phase peptide synthesis (SPPS). The resulting precursors were incubated with a cyclization-efficient AEP.
The team found that cyclization using six to nine-residue linkers did not perturb the overall structure of MVIIA. The best analogue showed much higher stability than native MVIIA. The cyclic analogues still inhibit the voltage-gated calcium channel CaV2.2, although they are less active than the native substrate. Overall, the work shows that AEPs can cyclize structurally complex peptides, which could be useful to further improve the therapeutic value of conotoxins.
- A Chemo‐enzymatic Approach to Produce a Cyclic Analogue of the Analgesic Drug MVIIA (Ziconotide),
Yan Zhou, Peta J. Harvey, Johannes Koehbach, Lai Yue Chan, Alun Jones, Åsa Andersson, Irina Vetter, Thomas Durek, David J. Craik,
Angew. Chem. Int. Ed. 2023.