Angewandte Chemie Communications DOI: 10.1002/anie.200504548 2864 # 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2006, 45, 2864 – 2868 Controlling the coordination geometry of a metal center is the first step in preparing proteins capable of catalysis. Substitution of a single amino acid can shift an equilibrium of 3- and 4-coordinate Cd II – peptide complexes to proteins containing exclusively 3- or 4-coordinate metal sites. For details, see the communication by V. L. Pecoraro and co-workers on the following pages.