Minimal conformation of the α-conotoxin ImI for the α7 neuronal nicotinic acetylcholine receptor recognition:: correlated CD, NMR and binding studies

The alpha-ImI conotoxin, a selective potent inhibitor of the mammalian neuronal alpha 7 nicotinic acetylcholine receptor (n-AchR), was shown by point mutation or by L-alanine scanning to display two regions essential for bioactivity: the active site Asp(5)-Pro(6)-Arg(7) in the first loop and Trp(10) in the second loop. The deletion of the Cys(3),Cys(12) disulfide bond in the a-ImI scaffold, e.g. peptide II, had no effect on its binding affinity, CD spectra, NMR studies and structure calculations were carried out on the mild type alpha-ImI, the weakest analog (R7A) and peptide II (equipotent to alpha-ImI) in order to point out the conformational differences between these compounds, Then, an attempt to correlate the conformational data and the affinity results was proposed. CD and NMR data were identical for the R7A analog and alpha-ImI, revealing the crucial functional role of the Arg(7) Side chain. On the other hand, the scaffold of the first loop in peptide II was shown by NMR to represent the minimal conformation for the optimal interaction of the toxin with the neuronal alpha 7 n-AchR, Last, the beta-turn forming property of the 6th residue (Pro) in the active site of the alpha-ImI can he correlated with its affinity. (C) 1999 Federation of European Biochemical Societies.