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ABSTRACT: The design of artificial metalloenzymes has become an important topic in biological chemistry and inorganic chemistry due to the potential applications of artificial metalloenzymes in nanoscience and biotechnology. One of the general methods used to produce artificially metalloenzymes involves the encapsulation of non-natural metal cofactors within protein scaffolds. This method has been used in the construction of small artificial metalloproteins with high activity and selectivity. However, the important roles of protein assemblies have not yet been systematically investigated in this field, even though natural enzymatic systems employ protein assemblies as molecular scaffolds for elaborate enzymatic reactions. In recent years, the above-mentioned general strategy has been applied to functionalize protein assemblies such as protein cages and protein crystals. These assembled structures form confined interior environments, which can be used to accommodate metal complex catalysts and to prepare metal nanoparticles. The development of artificial metalloenzymes with hierarchically-assembled proteins would enable us to provide powerful tools for industrial and biological applications. In this Focus Review, we discuss the most significant recent research in this field as well as future directions.
Chemistry - An Asian Journal 05/2013; · 4.50 Impact Factor
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ABSTRACT: Bioinorganic chemistry is of growing importance in the fields of nanomaterial science and biotechnology. Coordination of metals by biological systems is a crucial step in intricate enzymatic reactions such as photosynthesis, nitrogen fixation and biomineralization. Although such systems employ protein assemblies as molecular scaffolds, the important roles of protein assemblies in coordination chemistry have not been systematically investigated and characterized. Many researchers are joining the field of bioinorganic chemistry to investigate the inorganic chemistry of protein assemblies. This area is emerging as an important next-generation research field in bioinorganic chemistry. This article reviews recent progress in rational design of protein assemblies in coordination chemistry for integration of catalytic reactions using metal complexes, preparation of mineral biomimetics, and mechanistic investigations of biomineralization processes with protein assemblies. The unique chemical properties of protein assemblies in the form of cages, tubes, and crystals are described in this review.
Chemical Communications 12/2012; · 6.17 Impact Factor
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ABSTRACT: Artificial metalloenzyme, composed of metal complex(es) and a host protein, is a promising way to mimic enzyme catalytic functions or develop novel enzyme-like catalysis. However, it is highly challenging to unveil the active site and exact reaction mechanism inside artificial metalloenzyme, which is the bottleneck in its rational design. We present a QM/MM study of the complicated reaction mechanism for the recently developed artificial metalloenzyme system, (Rh(nbd)·apo-Fr) (nbd = norbornadiene), which is composed of a rhodium complex [Rh(nbd)Cl](2) and the recombinant horse L-chain apo-Ferritin. We found that binding sites suggested by the X-ray crystal structure, i.e., sites A, B, and C, are only precursors/intermediates, not true active sites for polymerization of phenylacetylene (PA). A new hydrophobic site, which we name D, is suggested to be the most plausible active site for polymerization. Active site D is generated after coordination of first monomer PA by extrusion of the Rh(I)(PA) complex to a hydrophobic pocket near site B. Polymerization occurs in site D via a Rh(I)-insertion mechanism. A specific "hydrophobic region" composed by the hydrophobic active site D, the nonpolar 4-fold channel, and other hydrophobic residues nearby is found to facilitate accumulation, coordination, and insertion of PA for polymerization. Our results also demonstrate that the hydrophobic active site D can retain the native regio- and stereoselectivity of the Rh-catalyzed polymerization of PA without protein. This study highlights the importance of theoretical study in mechanistic elucidation and rational design of artificial metalloenzymes, indicating that even with X-ray crystal structures at hand we may still be far from fully understanding the active site and catalytic mechanism of artificial metalloenzymes.
Journal of the American Chemical Society 09/2012; 134(37):15418-29. · 9.91 Impact Factor
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ABSTRACT: We have succeeded in preparing semi-synthesized proteins bound to Sc(3+) ion which can promote an epoxide ring-opening reaction. The Sc(3+) binding site was created on the surface of [(gp5βf)(3)](2) (N. Yokoi et al., Small, 2010, 6, 1873) by introducing a cysteine residue for conjugation of a bpy moiety using a thiol-maleimide coupling reaction. Three cysteine mutants [(gp5βf_X)(3)](2) (X = G18C, L47C, N51C) were prepared to introduce a bpy in different positions because it had been reported that Sc(3+) ion can serve as a Lewis-acid catalyst for an epoxide ring-opening reaction upon binding of epoxide to bpy and two -ROH groups. G18C_bpy with Sc(3+) can accelerate the rate of catalysis of the epoxide ring-opening reaction and has the highest rate of conversion among the three mutants. The value is more than 20 times higher than that of the mixtures of [(gp5βf)(3)](2)/2,2'-bipyridine and l-threonine/2,2'-bipyridine. The elevated activity was obtained by the cooperative effect of stabilizing the Sc(3+) coordination and accumulation of substrates on the protein surface. Thus, we expect that the semi-synthetic approach can provide insights into new rational design of artificial metalloenzymes.
Dalton Transactions 08/2012; 41(37):11424-7. · 3.84 Impact Factor
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ABSTRACT: Magnetic bimetallic CoPt nanoparticles are synthesized in the solvent channels of hen egg white lysozyme crystals by the reduction of Co(2+) and Pt(2+) ions pre-organized on the interior surface of the solvent channels. By using different lysozyme crystal systems, the magnetic properties of CoPt nanoparticles can be controlled.
Small 03/2012; 8(9):1314-9. · 8.35 Impact Factor
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ABSTRACT: Poly(phenylacetylene) (PPA) has versatile electrical and optical properties due to its intriguing π-conjugated backbone, configuration, stereoregularity, and helical conformation. Detailed DFT, ONIOM, and ONIOM-MD studies are presented to understand the mechanisms of Rh-catalyzed polymerization of phenylacetylene and the factors that control its regioselectivity and stereochemistry. The polymerization proceeds via the Rh(I) insertion mechanism (ΔH(‡) ≈ 9 kcal/mol), although all the Rh(I), Rh(III), and Rh-carbene types of active species are thermodynamically and kinetically plausible in solution; the Rh(III) insertion and the Rh-carbene metathesis mechanisms both have higher activation enthalpies (~22 and ~25 kcal/mol, respectively). Phenylacetylene prefers a 2,1-inserion, leading to head-to-tail regioselective PPA via a unique π-conjugative transition state. This π-conjugative characteristic specifically favors the 2,1-insertion due to the steric repulsion. Kinetic factors play a key role in the stereoregularity. The polymerization adopting a cis-transoidal conformation is the most favorable. The kinetic difference for the insertion originates in the conformational constraints of the parent propagation chain in the transition state. These fundamental guidelines should help advance the development of efficient and structurally tailorable PPA catalysts.
Journal of the American Chemical Society 05/2011; 133(20):7926-41. · 9.91 Impact Factor
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Angewandte Chemie International Edition 05/2011; 50(21):4849-52. · 13.45 Impact Factor
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Norihiko Yokoi,
Yuki Miura,
Chen-Yuang Huang,
Nobuyuki Takatani,
Hiroshi Inaba,
Tomomi Koshiyama,
Shuji Kanamaru,
Fumio Arisaka,
Yoshihito Watanabe,
Susumu Kitagawa, Takafumi Ueno
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ABSTRACT: We have constructed a robust β-helical nanotube from the component proteins of bacteriophage T4 and modified this nanotube with Ru(II)(bpy)(3) and Re(I)(bpy)(CO)(3)Cl complexes. The photocatalytic system arranged on the tube catalyzes the reduction of CO(2) with higher reactivity than that of the mixture of the monomeric forms.
Chemical Communications 02/2011; 47(7):2074-6. · 6.17 Impact Factor
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ABSTRACT: Apo-ferritin (apo-Fr) mutants are used as scaffolds to accommodate palladium (allyl) complexes. Various coordination arrangements of the Pd complexes are achieved by adjusting the positions of cysteine and histidine residues on the interior surface of the apo-Fr cage.
Chemical Communications 01/2011; 47(1):170-2. · 6.17 Impact Factor
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Yusuke Takezawa,
Philipp Böckmann,
Naoki Sugi,
Ziyue Wang,
Satoshi Abe,
Tatsuya Murakami,
Tatsuo Hikage,
Gerhard Erker,
Yoshihito Watanabe,
Susumu Kitagawa, Takafumi Ueno
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ABSTRACT: Spherical protein cages such as an iron storage protein, ferritin, have great potential as nanometer-scale capsules to assemble and store metal ions and complexes. We report herein the synthesis of a composite of an apo-ferritin cage and Ru(p-cymene) complexes. Ru complexes were efficiently incorporated into the ferritin cavity without degradation of its cage structure. X-Ray crystallography revealed that the Ru complexes were immobilized on the interior surface of the cage mainly by the coordination of histidine residues.
Dalton Transactions 11/2010; 40(10):2190-5. · 3.84 Impact Factor
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Norihiko Yokoi,
Hiroshi Inaba,
Makoto Terauchi,
Adam Z Stieg,
Nusrat J M Sanghamitra,
Tomomi Koshiyama,
Katsuhide Yutani,
Shuji Kanamaru,
Fumio Arisaka,
Tatsuo Hikage,
Atsuo Suzuki,
Takashi Yamane,
James K Gimzewski,
Yoshihito Watanabe,
Susumu Kitagawa, Takafumi Ueno
Small 09/2010; 6(17):1873-9. · 8.35 Impact Factor
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ABSTRACT: Hybridization of metal complexes and protein scaffolds is an important subject in bioinorganic chemistry and materials science. Efforts to provide non-natural functions to proteins will likely lead to advances in development of catalysts, sensors, and so on. Mechanistic investigations of the process of binding of metal complexes within protein scaffolds and characterization of the resulting coordination structures will help us to design and control coordination structures of metal complexes for construction of hybrid proteins containing metal complexes. In this work, the processes of accumulation and incorporation of organometallic palladium complexes within the cage of the iron storage protein apo-ferritin (apo-Fr) are elucidated by analysis of X-ray crystal structures of apo-Fr and selected mutants thereof, in the presence of the metal complexes. The crystal structure of apo-Fr containing Pd(allyl) (allyl = eta(3)-C(3)H(5)) complexes shows that thiolato-bridged dinuclear Pd(allyl) complexes are formed at two binding sites within the cage of apo-Fr. The crystal structures of apo-Fr and its Cys- and His-deletion mutants containing Pd(allyl) complexes indicate that Cys126 accelerates the incorporation of Pd(allyl) complexes into the cage. In addition, Cys48 and Cys126 are essential for accumulation of Pd(allyl) complexes and stabilizing the square planar coordination structure.
Inorganic Chemistry 08/2010; 49(15):6967-73. · 4.60 Impact Factor
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Takafumi Ueno
Angewandte Chemie International Edition 05/2010; 49(23):3868-9. · 13.45 Impact Factor
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ABSTRACT: Protein assemblies have attracted increasing attention for construction of biohybrid materials. Protein crystals can also be regarded as solid protein assemblies. The present work demonstrates that protein crystals can be employed as porous biomaterials by site-specific modifications of the crystals of recombinant sperm whale myoglobin mutants. The myoglobin crystals of space group P6 provide hexagonal pores consisting of the building blocks of six Mb molecules, which form a pore with a diameter of 40 A. On the basis of the lattice structure of the Mb crystals, we have selected appropriate residues located on the surface of the pores for replacement with cysteine. This enables modification of the pore surface via coupling with maleimide derivatives. We have succeeded in crystallizing the modified Mb mutants, retaining the P6 lattice, and consistently aligning nanosized functional molecules such as fluorescein, eosin, and Ru(bpy)(3) into the hexagonal pores of the Mb crystals. Our strategy for site-specific modification of protein crystal pores is applicable to various protein crystals with porous structures. We believe that modified porous protein crystals will provide attractive candidates for novel solid materials in nanotechnology applications.
Bioconjugate Chemistry 02/2010; 21(2):264-9. · 4.93 Impact Factor
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ABSTRACT: Metal-ion accumulation on protein surfaces is a crucial step in the initiation of small-metal clusters and the formation of inorganic materials in nature. This event is expected to control the nucleation, growth, and position of the materials. There remain many unknowns, as to how proteins affect the initial process at the atomic level, although multistep assembly processes of the materials formation by both native and model systems have been clarified at the macroscopic level. Herein the cooperative effects of amino acids and hydrogen bonds promoting metal accumulation reactions are clarified by using porous hen egg white lysozyme (HEWL) crystals containing Rh(III) ions, as model protein surfaces for the reactions. The experimental results reveal noteworthy implications for initiation of metal accumulation, which involve highly cooperative dynamics of amino acids and hydrogen bonds: i) Disruption of hydrogen bonds can induce conformational changes of amino-acid residues to capture Rh(III) ions. ii) Water molecules pre-organized by hydrogen bonds can stabilize Rh(III) coordination as aqua ligands. iii) Water molecules participating in hydrogen bonds with amino-acid residues can be replaced by Rh(III) ions to form polynuclear structures with the residues. iv) Rh(III) aqua complexes are retained on amino-acid residues through stabilizing hydrogen bonds even at low pH (approximately 2). These metal-protein interactions including hydrogen bonds may promote native metal accumulation reactions and also may be useful in the preparation of new inorganic materials that incorporate proteins.
Chemistry 02/2010; 16(9):2730-40. · 5.93 Impact Factor
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ABSTRACT: We have succeeded in preparing Au/Pd core-shell nanoparticles in apo-ferritin and improving the catalytic reactivity of olefin hydrogenation relative to Pd0 nanoparticles in the cage.
Chemical Communications 09/2009; · 6.17 Impact Factor
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ABSTRACT: Protein assemblies, such as viruses and ferritins, have been employed as useful molecular templates for the accumulation of organic and inorganic compounds to construct bio-nanomaterials. While several methods for conjugation of heterofunctional molecules with protein assemblies have been reported, it remains difficult to control their fixation sites in the assemblies. In this article, we demonstrate the three-dimensional arrangement of different types of fluorescent probes using the heteromeric self-assembly of (gp27-gp5)(3) which is the component protein of bacteriophage T4 (gp: gene product). The composites exhibited fluorescence resonance energy transfer from fluorescein to tetramethylrhodamine dyes immobilized in the bio-nanocup space. The alternation of the donor and acceptor positions induced fluorescence self-quenching by the formation of ground-state complexes of the acceptors. These results indicate that the site-specific conjugation method using the bio-nanocup space of the heteromeric protein assembly has potential for the integration of several types of functional molecules in protein nanospaces.
Organic & Biomolecular Chemistry 07/2009; 7(12):2649-54. · 3.70 Impact Factor
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ABSTRACT: Polymerization reactions of phenylacetylene derivatives are promoted by rhodium complexes within the discrete space of apo-ferritin in aqueous media. The catalytic reaction provides polymers with restricted molecular weight and a narrow molecular weight distribution. These results suggest that protein nanocages have potential for use as various reaction spaces through immobilization of metal catalysts on the interior surfaces of the protein cages.
Journal of the American Chemical Society 06/2009; 131(20):6958-60. · 9.91 Impact Factor
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ABSTRACT: Accumulation of metal ions on protein surfaces is an important subject in the field of materials science because these processes are applicable to the preparation of bioinspired inorganic materials. While previous studies related to this subject have focused on the preparation of nanomaterials using protein scaffolds, the detailed processes of metal ion deposition and metal core formation on a protein surface require clarification. Elucidation of the coordination structures of multinuclear metal binding sites on proteins at an early stage as well as intermediate and fully occupied stages of the metal ion deposition will help us to understand the reaction mechanisms so that desirable inorganic materials can be prepared using protein scaffolds. In this Article, we report on the detailed processes of accumulation of Pd(II) ions demonstrated by a series of X-ray crystal structural analyses of apo-ferritin (apo-Fr), an iron storage protein, containing different amounts of Pd(II) ions in the protein cage. We have identified the specific binding sites of Pd(II) ions and analyzed the dynamic changes in the coordination structure by a combination of the crystal structures and ICP quantitative analyses of apo-Fr containing low, intermediate, and high content of Pd(II) ions. Our studies on Pd(II).apo-Frs provide intriguing implications for the preparation of many other inorganic materials using protein surfaces.
Journal of the American Chemical Society 05/2009; 131(14):5094-100. · 9.91 Impact Factor
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ABSTRACT: Molecular design of artificial metalloproteins is one of the most attractive subjects in bioinorganic chemistry. Protein vacant
space has been utilized to prepare metalloproteins because it provides a unique chemical environment for application to catalysts
and to biomaterials bearing electronic, magnetic, and medical properties. Recently, X-ray crystal structural analysis has
increased in this research area because it is a powerful tool for understanding the interactions of metal complexes and protein
scaffolds, and for providing rational design of these composites. This chapter reviews the recent studies on the preparation
methods and X-ray crystal structural analyses of metal/protein composites, and their functions as catalysts, metal-drugs,
etc.
KeywordsCatalytic reaction-Metal-drugs-Metal materials-Nanocage-Protein-X-ray crystal structure
02/2009: pages 25-43;
