3-DIMENSIONAL SOLUTION STRUCTURE OF CONOTOXIN PSI-PIIIE, AN ACETYLCHOLINE GATED ION-CHANNEL ANTAGONIST

The three-dimensional structure of conotoxin psi-PIIIE, a 24-amino aci d peptide from Conus purpurascens, has been solved using two-dimension al (2D) H-1 NMR spectroscopy. Conotoxin psi-PIIIE contains the same di sulfide bending pattern as the mu-conotoxins, which target skeletal mu scle sodium channels, but has been shown to antagonize the acetylcholi ne gated cation channel through a noncompetitive mechanism. Structural information was obtained by the analysis of a series of 2D NOESY spec tra as well as measurement of coupling constants from 1D H-1 and PE-CO SY NMR experiments. Molecular modeling calculations included the use o f the distance geometry (DG) algorithm, simulated annealing techniques , and the restrained molecular dynamics method. The resulting structur es are considerably similar to the previously published structures for the mu-conotoxins GIIIA and GIIIB, despite the lack of sequence conse rvation between conotoxin psi-PIIIE and the mu-conotoxins. The structu re consists of a series of tight turns, each turn occurring in the pos ition analogous to those of turns described in mu-GIIIA and mu-GIIIB. This suggests the disulfide bonding pattern is able to largely direct the structure of the peptides, creating a stable structural motif whic h allows extensive sequence substitution of non-cystine residues.