Crystallography reveals metal-triggered restructuring of β-hairpins

Metal binding to β-sheets occurs in many metalloproteins and is also implicated in the pathology of Alzheimer's disease. De novo designed metallo-β-sheets have been pursued as models and mimics of these proteins. However, no crystal structures of canonical β-sheet metallopeptides have yet been obtained, in stark contrast to many examples for ɑ-helical metallopeptides, leading to a poor understanding for their chemistry. To address this, we have engineered tryptophan zippers, stable 12-residue β-sheet peptides, to bind Cu(II) ions and obtained crystal structures through single crystal X-ray diffraction (SC-XRD). We find that metal binding triggers several unexpected supramolecular assemblies that demonstrate the range of higher-order structures available to metallo-β-sheets. Overall, these findings underscore the importance of crystallography in elucidating the rich structural landscape of metallo-β-sheet peptides.