Self-oxidation of cysteine to sulfinic acid in an engineered T67C myoglobin: structure and reactivity

Myoglobin (Mb) was found to undergo self-oxidation when a cysteine residue was engineered at position 67 in the heme distal site. Both the X-ray crystal structure and mass spectrum confirmed the formation of a sulfinic acid (Cys–SO₂H). Moreover, the self-oxidation could be controlled during protein purification to yield the unmodified form (T67C Mb). Importantly, both T67C Mb and T67C Mb (Cys–SO₂H) were able to be labeled by chemicals, which provided useful platforms to generate artificial proteins.