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Cover Picture: Complex Gadolinium–Oxo Clusters Formed along Concave Protein Surfaces (ChemBioChem 15/2012)
The cover picture shows the assembly of a complex gadolinium cluster (gold) along a unique, acidic surface patch of the yeast cell adhesion domain Flo5A that was formally identified as a secondary carbohydrate binding site. The step-wise formation of this heptanuclear gadolinium complex in crystals of Flo5A mimics the nucleation and deposition of iron-oxo clusters along ferritin surfaces. In the communication on p. 2187 ff., L.-O. Essen and M. Veelders show that the complex's unprecedented composite structure, which consists of a distorted Gd4O4 cubane and a trinuclear Gd3O5 cluster, requires coordination to four aspartic acid residues of the protein. Incorporation of the gadolinium cluster on the protein surface depends on the early formation of μ-oxo-bridged lanthanide cores. The observation that aspartates suitably placed on protein surfaces foster gadolinium cluster formation constitutes a paradigm for protein-based biohybrids carrying metallo-oxo clusters. This could, in future, lead to the design of protein-based templates for polynuclear gadolinium complexes and hence to site-specific and biocompatible MRI contrast agents.