Bipartite tetracysteine display requires site flexibility for ReAsH coordination.

Flexibility required: We designed intramolecular bipartite tetracysteine sites in loops of p53 and the beta-sheets of EmGFP. We found that ReAsH binding preferentially favors tetracysteine sites with flexible geometries such as loops; flexibility was assessed by comparing Calpha B-factor values. This information is important for directing successful bipartite tetracysteine site designs.