The Red Color of Life Transformed - Synthetic Advances and Emerging Applications of Protoporphyrin IX in Chemical Biology

Protoporphyrin IX (PPIX) is the porphyrin scaffold of heme b, a ubiquitous prosthetic group of proteins responsible for oxygen binding (hemoglobin, myoglobin), electron transfer (cytochrome c) and catalysis (cytochrome P450, catalases, peroxidases). PPIX and its metallated derivatives frequently find application as therapeutic agents, imaging tools, catalysts, sensors and in light harvesting. The vast toolkit of accessible porphyrin functionalization reactions enables easy synthetic modification of PPIX to meet the requirements for its multiple uses. In the past few years, particular interest has arisen in exploiting the interaction of PPIX and its synthetic derivatives with biomolecules such as DNA and heme-binding proteins to evolve molecular devices with new functions as well as to uncover potential therapeutic toeholds. This review strives to shine a light on the most recent developments in the synthetic chemistry of PPIX and its uses in selected fields of chemical biology.

Interdomain flip-flop motion visualized in flavocytochrome cellobiose dehydrogenase using high-speed atomic force microscopy during catalysis

To visualize the dynamic domain motion of class-I CDH from Phanerochaete chrysosporium (PcCDH) during catalysis using high-speed atomic force microscopy, the apo-form of PcCDH was anchored to a heme-immobilized flat gold surface that can fix the orientation of the CYT domain.

Cellobiose dehydrogenase (CDH) is a dual domain flavocytochrome, which consists of a dehydrogenase (DH) domain containing a flavin adenine dinucleotide and a cytochrome (CYT) domain containing b-type heme. To directly visualize the dynamic domain motion of class-I CDH from Phanerochaete chrysosporium (PcCDH) during catalysis using high-speed atomic force microscopy, the apo-form of PcCDH was anchored to a heme-immobilized flat gold surface that can specifically fix the orientation of the CYT domain. The two domains of CDH are found to be immobile in the absence of cellobiose, whereas the addition of cellobiose triggers an interdomain flip-flop motion involving domain–domain association and dissociation. Our results indicate that dynamic motion of a dual domain enzyme during catalysis induces efficient electron transfer to an external electron acceptor.

Cofactor-specific covalent anchoring of cytochrome b562on a single-walled carbon nanotube by click chemistry

Redox-active cytochromeb₅₆₂with a tethered azide group on the heme propionate side chain is covalently linked to an acetylene moiety introduced on the sidewall of a single-walled carbon nanotube by copper-catalyzed click chemistry.

Hemoprotein-based supramolecular assembling systems

Hemoproteins are metalloproteins which include iron porphyrin as a cofactor. These proteins have received much attention as promising building blocks for development of new types of biomaterials. This review summarizes recent efforts in the rational design of supramolecular hemoprotein assemblies using myoglobin, horseradish peroxidase, cytochrome b562 and cytochrome c as a monomer unit. The processes of coordination bond-mediated assembly or domain swapping-mediated assembly provide defined oligomers, while hemoprotein reconstitution with synthetic heme derivatives provides submicrometer-sized structures such as fibrils, vesicles/micelles, or networks. Interestingly, several of these assembled structures maintain the intrinsic functions of monomer units. The chemical and/or biological strategies described in this review will lead to the creation of unique hemoprotein-based functional biomaterials.