Hydrolytically active Eu(III) and Ce(IV) EF-hand peptides.

A chimeric peptide (P4) has been designed to incorporate an EF-hand metal-binding loop into the context of the helix-turn-helix DNA binding motif of the engrailed homeodomain. This construct binds lanthanides, and in the presence of these metals, promotes the cleavage of supercoiled DNA and model phosphate esters (bisnitrophenyl phosphate). P4 binds lanthanides with moderate affinities (Eu(III), log Ka=4.85; and Ce(IV), log Ka=5.23). The structure of P4 is enhanced by metal binding, but the increase in secondary structure observed by CD is small, and suggests the metallopeptide is also quite flexible. Despite this flexibility, the efficient cleavage of DNA at low concentrations is dependent on the metallopeptide, and not on peptide or metal alone. This enhanced reactivity suggests the designed DNA-binding EF-hand peptides deliver the metal to the DNA for catalysis, even without rigid secondary structure.