The mythical metal – insights on the accuracy of metal identification in structural biology

The Protein Data Bank (PDB) contains information on more than 200,000 proteins. Some 25 - 50% of all proteins contain one or more metals or metal co-factors playing a key structural or catalytic role. Metalloproteins can be difficult targets for structural studies because the specific metals required for enzymatic activity are not always those with the highest binding affinity. To incorporate uncompetitive metals into an enzyme active site, cells have evolved sophisticated machinery, including metal transporters and chaperones, which are often bypassed during protein production in the laboratory. The problem of metal promiscuity is compounded by the difficulty of accurately identifying incorporated metals. In many cases, the small sample volumes available confound the issue. Using