Poster Presentation 10th Australian Peptide Conference 2013

Dicarba α–conotoxin Vc1.1 analogues with differential selectivity for nicotinic acetylcholine and GABAB receptors (#146)

Alessia Belgi 1 , Bianca J van Lierop 1 , Samuel D Robinson 2 , Shiva N Kompella 3 , Jeffrey R McArthur 3 , Andrew Hung 3 , Christopher MacRaild 2 , David J Adams 3 , Raymond S Norton 2 , Andrea J Robinson 1
  1. Monash University, Clayton, VIC, Australia
  2. Monash Institute of Pharmaceutical Sciences, Parkville, VIC, Australia
  3. Health Innovations Research Institute, RMIT University, Melbourne, VIC, Australia

The α-conotoxin Vc1.1 is a peptide extracted from the venom of the cone snail Conus victoriae 1. Specifically, Vc1.1 is a 16-residue peptide with an amidated C-terminus and four cysteine residues which form two cystine bridges with the connectivity CysI-CysIII, CysII-CysIV 2. It acts both as antagonist on the α9α10 subtype of nicotinic acetylcholine receptors (nAChRs) and as an agonist on γ–aminobutyric acid (GABAB) G protein-coupled receptors showing a potent analgesic activity 3,4. The mechanism by which Vc1.1 exerts its analgesic effect has not been fully elucidated yet.

In the present study, each disulfide bond of Vc1.1 was replaced with an unsaturated dicarba bond using a technique successfully developed within our group and applied to several peptidomimetic studies 5,6,7. This mutation is an invaluable tool in determining whether a disulfide bond within a peptide plays a functional or structural role. Four dicarba Vc1.1 analogues were obtained: cis-[2,8]-dicarba Vc1.1, trans-[2,8]-dicarba Vc1.1, from the substitution of the CysI-CysIII bridge, and cis-[3,16]-dicarba Vc1.1 and trans-[3,16]-dicarba Vc1.1 from the replacement of the CysII-CysIV bridge.

NMR spectroscopy showed that the structures of cis-[2,8]-dicarba Vc1.1, cis-[3,16]-dicarba Vc1.1 and trans-[3,16]-dicarba Vc1.1 are almost identical to the structure of native Vc1.13 confirming that the dicarba mutation is well tolerated by the peptide.

The activity of the dicarba analogues was assessed in vitro on α9α10 nAChRs and the GABAB receptor 3. The two [2,8]-dicarba Vc1.1 analogues were both only active on GABAB receptor, conversely the two [3,16]-dicarba Vc1.1 analogues were both only active on the α9α10 nAChRs. These findings highlight the importance of the disulfide bonds in regulating structure and function of the native Vc1.1 peptide.

 Selected dicarba analogues are currently being assessed in animal models of pain to gain further insights into their analgesic properties. These results will be presented in this paper.

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  3. van Lierop, B., Robinson, S. D., Kompella, S. N., Belgi, A., McArthur, J. R., Hung, A., MacRaild, C., Adams, D. J., Norton, R. S., and Robinson, A. J. (2013) Dicarba α-Conotoxin Vc1.1 Analogues with Differential Selectivity for Nicotinic Acetylcholine and GABAB Receptors, Chemical Biology accepted for publication June 2013.
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