Conformational change during the binding of Cu2+ and Zn2+ to the thiazole and oxazoline containing cyclic octapeptides, the patellamides, is examined by a combination of experimental and theoretical methods. Circular dichroism and NOE-restrained molecular dynamics studies indicate that upon complexing with one equivalent of Cu2+, patellamide C undergoes a change in conformation which pre-organises a second Cu2+ binding site, and that the binding of a second Cu2+ induces no further conformational change. The binding of Zn2+ induces little conformational change in patellamide C. A restrained conformational search shows that the conformational change induced by the addition of one equivalent of Cu2+ to patellamide C is an intrinsic design feature of the system. Electronic structure calculations indicate that the patellamides provide an ideal coordination environment for Cu2+. On the basis of the evidence gathered, it can be proposed that Cu2+ is the biologically relevant metal for the patellamides.

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