Conformational and ion-binding properties of cyclolinopeptide A isolated from linseed.

ABSTRACT

The conformation of the cyclic nonapeptide from linseed, cyclolinopeptide A in methanol and in acetonitrile has been elucidated by one- and two-dimensional nuclear magnetic resonance. The molecule is folded in a ß-turn conformation. Cyclolinopeptide A interacts and weakly complexes with Tb3+ (a Ca2+ mimic ion) with the metal ion positioned proximally to the Phe residue, but with no substantial structural alteration upon metal binding. Cyclolinopeptide A is also seen to aid the translocation of Pr3+ (another Ca2+ mimic) across unilamellar liposomes. However, cyclolinopeptide A does not phase transfer or act as an ionophore of calcium ion myself. Experiments using lanthanide ions thus do not necessarily indicate any ionophoretic ability of the complexone towards calcium ions.