Crystal structure of the channel-forming polypeptide antiamoebin in a membrane-mimetic environment

Abstract

Crystals of an ion-channel-forming peptaibol peptide in a partial membrane environment have been obtained by cocrystallizing antiamoebin with n-octanol. The antiamoebin molecule has a bent helical conformation very similar to that established for Leu-zervamicin, despite a significantly different sequence for residues 1-8. The bent helices assemble to form a polar channel in the shape of an hour glass that is quite comparable to that of Leu-zervamicin. The molecules of cocrystallized octanol are found in two different areas with respect to the assembly of peptide molecules. One octanol molecule mimics a membrane segment along the hydrophobic exterior of the channel assembly. The other octanol molecules fill the channel in such a way that their OH termini satisfy the C=O moieties directed into the interior of the channel. Structure parameters for C₈₂H₂₇N₁₇O₂₀.3C₈H₁₈O are space group P2₁2₁2₁, a = 9.143(2) Å, b = 28.590(8) Å, c = 44.289(8) Å, Z = 4, agreement factor R₁ = 11.95% for 4,113 observed ref lections [>4σ(F)], resolution ~ 1.0 Å.