title: The cyclic contryphan motif CPxXPXC, a robust scaffold potentially useful as an omega-conotoxin mimic.
abstract: Contryphan-R, from venom of the cone-shell Conus radiatus, represents a novel cyclic peptide scaffold onto which residues may be grafted to mimic unrelated protein surfaces. Three substitutions were made at the x and X positions of the disulfide-bridged motif CPxXPXC, where X and x represent any L- and D-handed residues, respectively, P represents proline or hydroxyproline, and C a half-cystine. These substitutions were designed to mimic part of the pharmacophore of the unrelated globular polypeptide omega-conotoxin GVIA, which blocks N-type calcium channels. The structure of this engineered contryphan, YNK-contryphan-R ([D-Tyr4, Asn5, Lys7]contryphan-R), is shown to be similar to that of native contryphan-R (Pallaghy et al., Biochemistry, 1999, Vol. 38, pp. 13553-13559), confirming that the scaffold is robust with respect to the multiple substitutions. In particular, the alpha-beta bond vectors characterising the orientation of the side chains relative to the backbone are similar in contryphan-R, YNK-contryphan-R, and omega-conotoxin GVIA, which is the required result for a scaffold-based approach to molecular design. The solution structure of YNK-contryphan-R has an N-terminal, nonhydrogen-bonded, chain reversal centered on Hyp3-D-Trp4, and a C-terminal type I beta-turn. A minor form due to cis-trans isomerism of the Hyp2-Cys3 peptide bond is present in YNK-contryphan-R in a larger proportion than in contryphan-R. It is evident, particularly from the (3)J(HalphaHN) coupling constants, that YNK-contryphan-R is more flexible than contryphan-R, probably due to the absence in YNK-contryphan-R of the Pro-Trp packing present in the native molecule. Nevertheless, the structure confirms that cyclic peptide molecular designs can achieve the intended conformations.
authors.affiliation: Biomolecular Research Institute, 343 Royal Parade, Parkville 3052, Australia. Paul.Pallaghy@bioresi.com.au
authors.forename: P K
authors.initials: PK
authors.lastname: Pallaghy
authors.forename: R S
authors.initials: RS
authors.lastname: Norton
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry; D015195:Drug Design; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D018716:Molecular Mimicry; D008978:Mollusk Venoms / Q000737:chemistry; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D020866:omega-Conotoxin GVIA / Q000737:chemistry*
chemical_list: D002121:Calcium Channel Blockers; D008978:Mollusk Venoms; D010456:Peptides, Cyclic; C102355:contryphan; D020866:omega-Conotoxin GVIA