Exploring Function With De Novo Proteins

A synthetic metalloprotein can be altered slightly to perform an entirely new function, illustrating the potential of these de novo proteins to serve as templates for studying metalloprotein activity (Nat. Chem., DOI: 10.1038/nchem.1454). William F. DeGrado of the University of California, San Francisco, and colleagues started with the di-iron carboxylate protein DFsc, which catalyzes O₂-dependent, two-electron oxidation of hydroquinones. Guided by computations, the group made small changes to the binding site of the original protein, substituting four alanines for glycines. The change widened the channel leading to the site, allowing a substrate easier access to the di-iron core. The resulting metalloprotein, G4DFsc, was better able to bind and oxidize 4-aminophenol to its corresponding quinone imine. The group also added a third metal-binding histidine residue to the binding site. This protein, dubbed 3His-G4Dfsc, catalyzed the selective N-hydroxylation of arylamines. In comparing the original and new proteins, the authors write, “we can begin to delineate the roles (geometric and electronic) of individual amino acids in endowing catalytic activities.”