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.
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