One strategy for understanding the origin of life is proposing simple replacements for the complex biomolecules that have developed through billions of years of evolution. Ferredoxins are small proteins that contain simple, cubic clusters of iron and sulfur atoms and act as mobile electron carriers in cells. Kim et al. designed a 12-residue peptide with alternating D and L amino acids that can replicate the placement of cysteine ligands found in many natural ferredoxins. After reconstitution with iron and sulfur, the peptides bound a single iron-sulfur cluster. The resulting minimal, artificial ferredoxin exhibited a redox potential compatible with some biological processes.