Biosynthesis of artificial microperoxidases by exploiting the secretion and cytochrome c maturation apparatuses of Escherichia coli

Microperoxidases were initially isolated as peptide fragments containing covalently bound heme and are derived from naturally occurring c-type cytochromes. They are not only used as model compounds but also have potential applications as biosensors, electron carriers, photoreceptors, microzymes, and drugs. In a systematic attempt to define the minimal requirements for covalent attachment of hemes to c-type cytochromes, we have succeeded to produce artificial microperoxidases with peptide sequences that do not occur naturally and can be manipulated. The in vivo production of these microperoxidases requires targeting of the peptide to the bacterial periplasm, proteolytic processing of the signal peptide, and covalent attachment of heme to the signature motif CXXCH by the cytochrome c maturation proteins CcmA-H. The peptides that bind heme carry a C-terminal histidine tag, presumably to stabilize the heme peptide. We present a heme cassette that is the basis for the de novo design of functional hemoproteins.