Cage Architecture and Reactivity are Preserved in Cysteine‐mutated Ferritin

The role of solvent-exposed cysteines as reactive sites for bioconjugation with a variety of metal drugs or fluorescent probes is emerging in the use of human H-ferritin (HuHf) as a nanocarrier for targeting various tumor cell lines. Here, we have investigated the role of these residues in controlling the structural stability and ferroxidase activity by analyzing the properties of three variants: C90A, C90AC102A, and C130A. Protein folding and cage assembly were unchanged. Ferroxidase activity was also unaffected, indicating that these cysteines are not involved in either the catalytic activity or the overall iron(II) uptake process. For comparison, activity measurements were also performed on two derivatives involving the solvent-exposed cysteine residues.