Modulation of cluster incorporation specificity in a de novo iron-sulfur cluster binding peptide

iron-sulfur cluster binding proteins perform an astounding variety of functions, and represent one of the most abundant classes of metalloproteins. Most often, they constitute pairs or chains and act as electron transfer modules either within complex redox enzymes or within small diffusible proteins. We have previously described the design of a three-helix bundle that can bind two clusters within its hydrophobic core. Here, we use single-point mutations to exchange one of the Cys ligands coordinating the cluster to either Leu or Ser. We show that the mutants modulate the redox potential of the clusters and stabilize the [3Fe-4S] form over the [4Fe-4S] form, supporting the use of model iron-sulfur cluster proteins as modules in the design of complex redox enzymes.