Phalloidin synthetic analogues: Structural requirements in the interactionwith F-actin

Synthetic derivatives of phalloidin have been investigated in solution by c ircular dichroism (CD) and NMR spectroscopy. They differ from natural phall oidin (PHD), bicyclo(Ala(1)-D-Thr(2)-Cys(3)-cis-4-hydroxy-Pro(4)-Ala(5)-2-m ereap-to-Trp(6)-(OH)(2)Leu(7))(S-3 --> 6), in that they are modified at pos itions 2, 3, and 7. Among these synthetic analogues, structural differences and varying degrees of atropisomerism are found. By comparing the respecti ve molecular models obtained by restrained molecular dynamics (RMD) simulat ions based on experimental NMR data, structural features that may be respon sible for the different biological behavior become apparent. Our results in dicate that the structural changes that result from an inversion of chirali ty of residue 3 lead to a complete loss of toxicity. Conversely, toxicity i s less affected by the structural changes that stem from an inversion of ch irality of residue 2. Moreover, unlike the other phallotoxins, when the thi oether unit bridges to the opposite face of the main peptide ring, in contr ast to the situation in other phallotoxins, large structural changes are ob served as well as a total loss of activity. Molecular models of the synthet ic phalloidin analogues have been used to investigate the necessary structu ral requirements for the interaction with F-actin. To this end, the F-actin /PHD model of M. Lorenz et al. was employed; docking experiments of our mol ecular models in the PHD binding site are presented.