Supramolecular assembling systems of hemoproteins using chemical modifications

Inspired by protein assemblies in biological systems, various artificial protein assemblies have been constructed in these decades. Hemoprotein containing porphyrin iron complex, heme, is a unique building block of the artificial protein assemblies due to the structures, physicochemical properties and functions. In the case of hemoprotein containing b-type heme, the heme cofactor is non-covalently bound to the heme-binding site, heme pocket, in the protein matrix. This review summaries our efforts to utilize heme–heme pocket interactions toward supramolecular hemoprotein assembling systems with various structures and/or functions. Simple monomeric hemoprotein, mainly cytochrome b₅₆₂, was employed as a useful building block and synthetic heme was attached to the cysteine-introduced variant to form a building block showing self-assembling behavior by interprotein heme–heme pocket interactions. The modulations of linker between synthetic heme and protein surface and/or protein modification site contribute to provide various structures such as fiber, ring, branched shape and micelles. Furthermore, hexameric hemoprotein was utilized for another building block with supramolecular approach toward light harvesting system by replacement of heme cofactors with porphyrinoid photosensitizers. A series of artificial hemoprotein assembling systems will contribute to new-type of functional biomaterials.