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 Catalytic Vessels for Organometallic Complexes

“…[8][9][10][11] Protein crystals represent precise protein assemblies in the solid state and, thus, are appropriate candidates for the development of robust biohybrid nanomaterials. [7,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Each protein crystal is a stable protein assembly with inner pores that act as "solvent channels". The sizes of these solvent channels vary according to the lattice of each individual crystal.…”

Porous Protein Crystals as Reaction Vessels

“…Accumulation of a Zn porphyrin and a Ru 3 O cluster in the solvent channels of Mb enabled the construction of a photoinduced, multistep, electron-transfer system with longlived charge separation. [34] When Zn-porphyrin-substituted hemeproteins are included in the crystals of natural redox protein complexes, electron-transfer reactions are initiated in the single crystal by light irradiation. [35] Ueno, et al prepared Zn-substituted Mb and obtained crystals with hexagonal solvent channels 40 wide.…”

“…[26] The time course of the X-ray crystal structure analysis indicated that the Au I atoms coordinating in the sol- The surface is colored with a spectrum (ranging from red to blue for the negative to positive charge of each residue). [34] Figure 7. a) The crystal lattice and b) the molecular structure of a HEWL crystal that contains Rh III ions. c) Snapshot analyses of Rh ion binding to Site B.…”

Artificial Metalloenzymes Constructed From Hierarchically‐Assembled Proteins

“…Figure 20). [112,113] Ru II A C H T U N G T R E N N U N G (bpy) 3 complexes were fixed in the channels through the cysteine and maleimide conjugation technique. After K102 was substituted with cysteine, K102C was modified with a RuA C H T U N G T R E N N U N G (bpy) 3 -maleimide derivative (4).…”

“…Dual accumulation of a Zn porphyrin and an Ru 3 O cluster in the solvent channels of Mb was performed to construct a photo-induced multistep electron transfer system with long-lived charge separation. [113] When Zn porphyrinsubstituted heme proteins are mixed with single crystals of natural redox protein complexes, electron transfer reactions are initiated in the single crystals by light irradiation. [96] Ueno et al prepared Zn-substituted Mb, and the resulting crystal was found to have 40 wide hexagonal solvent channels.…”