CRYSTAL-STRUCTURE OF THE CHANNEL-FORMING POLYPEPTIDE ANTIAMEBIN IN A MEMBRANE-MIMETIC ENVIRONMENT

Crystals of an ion-channel-forming peptaibol peptide in a partial memb rane environment have been obtained by cocrystallizing antiamoebin wit h n-octanol, The antiamoebin molecule has a bent helical conformation very similar to that established for Leu-zervamicin, despite a signifi cantly 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 co mparable to that of Leu-zervamicin. The molecules of cocrystallized oc tanol are found in two different areas with respect to the assembly of peptide molecules. One octanol molecule mimics a membrane segment alo ng the hydrophobic exterior of the channel assembly. The other octanol molecules fill the channel in such a way that their OH termini satisf y the C=O moieties directed into the interior of the channel. Structur e parameters for C82H27N17O20. 3C(8)H(18)O are space group P2(1)2(1)2( 1), a = 9.143(2) Angstrom, b = 28.590(8) Angstrom, c = 44.289(8) Angst rom, Z = 4, agreement factor R-1 = 11.95% for 4,113 observed reflectio ns [>4 sigma(F)], resolution similar to 1.0 Angstrom.