Post‐Crystal Engineering of Zinc‐Substituted Myoglobin to Construct a Long‐Lived Photoinduced Charge‐Separation System

Abstract

Photoinduced electron transfer (ET) in native photosynthesis reactions is efficiently achieved by the accumulation of different types of redox cofactors within protein assemblies immobilized in cell membranes. [1][2][3] The precise arrangement of each cofactor in the molecular spaces enables them to retain the long-lived charge-separated state, which promotes multistep reactions in biological systems. To elucidate the mechanism of the biological ET reactions and to develop light energy conversion systems, artificial ET proteins have been constructed using de novo proteins, chemical modification of native cofactors, photocatalytic reaction centers engineered into protein assemblies, and design of synthetic metal complexes immobilized in protein-protein ET systems. [4][5][6][7][8][9][10][11][12] The reported systems have provided insights into control of ET rates in terms of the distance between donors and acceptors, hydrogen-bonding interactions, reorganization energy of cofactors, and other factors. [4][5][6][7][8][9][10][11][12] Control of the dense accumulation of the different redox cofactors observed in natural photosystems required to achieve long-lived charge-separated state has caused difficulties in efforts to duplicate this process using artificial protein systems in solution.[13] Thus, the design of novel protein frameworks that allow construction of a dense array of various cofactors is a worthwhile goal. Protein crystals can be regarded as excellent candidates for the development of artificial ET reaction systems because the crystal lattices are expected to allow different types of cofactors to be arranged in three-dimensional frameworks that mimic the native ET systems. ET reactions in single protein crystals have been investigated for the dependence of long-range ET on the structures and orientations of redox centers within proteins. [14][15][16] Gray et al. constructed photochemically-initiated protein-protein ET reactions in protein crystals containing zinc-substituted cytochrome c peroxidase or ruthenium-modified azurin. [14][15][16] Moreover, protein crystals provide nanosized spaces for the fixation of metal ions, metal complexes, and the diffusion of organic molecules. [17][18][19][20][21][22] For instance, accumulation of metal ions and metal complexes in a protein crystal lattice spaces was accomplished simply by soaking of the crystals in a solution containing their precursors. [17][18][19] Anisotropic diffusion of small molecules in hen egg-white lysozyme (HEWL) crystals has been investigated by experimental and simulation approaches. [21,22] The results suggest that these features are governed by steric repulsion and electrostatic interaction induced by amino acid residues located on the internal surface of the crystal lattices. Thus, if we can precisely arrange donor and acceptor molecules and mediators in protein crystals, it is expected that the novel three-dimensional framework will allow us to achieve a longlived charge-separated state.Herein, we construct an artificial long-lived ph...

Porous Protein Crystals as Reaction Vessels for Controlling Magnetic Properties of Nanoparticles

“…These crystals are able to capture and deposit metal ions and metal complexes within solvent channels when the crystals are soaked in the solutions containing the metal ions because the amino acid side chains responsible for coordinating the metal ions are periodically aligned on the surface of solvent channels of the crystal lattices 17–22. We have demonstrated the accumulation of functional molecules such as metal complexes and metal clusters into the solvent channels of porous myoglobin crystals by chemical conjugation and coordination interactions 23, 24. With respect to inorganic materials, it has been reported that protein crystals can serve as nanoreactors for the preparation of nanoparticles 25, 26.…”

Overcoming the Incompatibility Challenge in Chemoenzymatic and Multi‐Catalytic Cascade Reactions

“…Koshiyama and co‐workers constructed an artificial long‐lived photo‐induced charge‐separation system using a single myoglobin (from sperm whale) crystal with different redox cofactors fixed in defined locations . Methyl viologen (MV) mediated the electron transfer between Zn porphyrin (ZnP, electron donor) and an oxo‐centered triruthenium cluster (Ru 3 O), electron acceptor) in the crystal.…”

Spectroscopic and Computational Study of a Nonheme Iron Nitrosyl Center in a Biosynthetic Model of Nitric Oxide Reductase

“…[7a] After extracting its heme using a slightly modified method from the literature (see the SI), [10] the protein was reconstituted with ZnPP (Figure 1). The UV-vis spectrum of ZnPP-reconstituted protein, ZnPPFe B Mb1, has absorption peaks at 427 nm, 553 nm, and 595 nm (Figure 2).…”