Akira Onoda

Highly oriented aragonite nanocrystal–biopolymer composites in an aragonite brick of the nacreous layer of Pinctada fucata

13C CP/MAS NMR and FE/TEM measurements of the aragonite brick of the nacreous layer of Pinctada fucata indicate that it assembles with highly oriented aragonite nanocrystals, which are regulated by biopolymers.

Chemically Programmed Supramolecular Assembly of Hemoprotein and Streptavidin with Alternating Alignment

Alternating: a cofactor dyad consisting of a heme group (red in picture) and a bis(biotin) unit (blue) was synthesized and shown to specifically bind to both apomyoglobin and streptavidin. In the presence of the dyad, the 1:1 association of a disulfide-bridged myoglobin dimer (green) with streptavidin (gray) afforded a submicrometer-sized fibrous alternating copolymer.

A chemically-controlled supramolecular protein polymer formed by a myoglobin-based self-assembly system

Artificial self-assembling systems comprised of proteins have the potential not only for mimicking naturally occurring protein clusters but also for creating functionalized supramolecular polymers. Here we report a new type of a supramolecular protein polymer which utilizes the original character and reactivity of the monomer protein. Myoglobin, an oxygen storage hemoprotein, was chosen as the monomer unit and was provided with an externally-attached heme on the protein surface which drives the formation of the fibrous supramolecular assembly through successive interprotein interactions between the external heme and the protein matrix. This assembly governed by myoglobin characteristics shows chemically-responsive stability and can be converted into extremely large protein clustersvia cross-linking. Interestingly, the assembly retains the oxygen storage function. Our present system can be used for construction of smart nanobiomaterials using various hemoproteins.

Fabrication of enzyme-degradable and size-controlled protein nanowires using single particle nano-fabrication technique

Protein nanowires exhibiting specific biological activities hold promise for interacting with living cells and controlling and predicting biological responses such as apoptosis, endocytosis and cell adhesion. Here we report the result of the interaction of a single high-energy charged particle with protein molecules, giving size-controlled protein nanowires with an ultra-high aspect ratio of over 1,000. Degradation of the human serum albumin nanowires was examined using trypsin. The biotinylated human serum albumin nanowires bound avidin, demonstrating the high affinity of the nanowires. Human serum albumin–avidin hybrid nanowires were also fabricated from a solid state mixture and exhibited good mechanical strength in phosphate-buffered saline. The biotinylated human serum albumin nanowires can be transformed into nanowires exhibiting a biological function such as avidin–biotinyl interactions and peroxidase activity. The present technique is a versatile platform for functionalizing the surface of any protein molecule with an extremely large surface area.

Artificial hydrogenase: biomimetic approaches controlling active molecular catalysts.

Hydrogenase catalyses reversible transformation of H2 to H(+) using an active site which includes an iron or nickel atom. Synthetic model complexes and molecular catalysts inspired by nature have unveiled the structural and functional basis of the active site with remarkable accuracy and this has led to the discovery of active synthetic catalysts. To further improve the activity of such molecular catalysts, both the first and outer coordination spheres should be well-organized and harmonized for an efficient shuttling of H(+), electrons, and H2. This article reviews recent advances in the design and catalytic properties of artificial enzymes that mimic the hydrogenase active site and the outer coordination sphere in combination with a peptide or protein scaffold.

meso‐Dibenzoporphycene has a Large Bathochromic Shift and a Porphycene Framework with an Unusual cis Tautomeric Form

meso-Monobenzoporphycene (mMBPc) and meso-dibenzoporphycene (mDBPc), in which one or two benzene moieties are fused at ethylene-bridged positions (meso-positions) of porphycene, were prepared in an effort to further delocalize the π-electrons within the porphycene molecule. mMBPc and mDBPc were fully characterized by mass spectrometry, (1)H and (13)C NMR spectroscopy, and X-ray crystallography. The longest-wavelength Q-bands of mMBPc and mDBPc are red-shifted by 92 nm and 418 nm, respectively, compared to that of the unsubstituted porphycene (Pc). Electrochemical measurements indicate that the HOMO is destabilized and the LUMO is stabilized by the fused benzene moieties at the meso positions. Furthermore, both XPS and theoretical studies support the presence of a cis tautomeric form in the ground state of mDBPc, despite the fact that essentially all known porphycene derivatives adopt the trans tautomeric form.

Crystal structure and spectroscopic studies of a stable mixed-valent state of the hemerythrin-like domain of a bacterial chemotaxis protein.

The bacterial chemotaxis protein of Desulfovibrio vulgaris DcrH (DcrH-Hr) functions as an O(2)-sensing protein. This protein has a hemerythrin-like domain that includes a nonheme diiron center analogous to the diiron center of the hemerythrin (Hr) family. Interestingly, the O(2) affinity of DcrH-Hr is 3.3 × 10(6) M(-1), a value 25-fold higher than that of the Pectinaria gouldii Hr. This high affinity arises from the fast association of the O(2) ligand with DcrH-Hr (k(on) = 5.3 × 10(8) M(-1) s(-1)), which is made possible by a hydrophobic tunnel that accelerates the passage of the O(2) ligand to the diiron site. Furthermore, the autoxidation kinetics indicate that the rate of autoxidation of DcrH-Hr is 54-fold higher than that of P. gouldii Hr, indicating that the oxy form of DcrH-Hr is not stable toward autoxidation. More importantly, a mixed-valent state, semimet(R), which was spectroscopically observed in previous Hr studies, was found to be stable for over 1 week and isolable in the case of DcrH-Hr. The high-resolution crystal structures of the semimet(R)- (1.8 Å) and met-DcrH-Hr (1.4 Å) indicate that the semimet(R)- and met-DcrH-Hr species have very similar coordination geometry at the diiron site.

Photochemical properties of a myoglobin–CdTe quantum dot conjugate

A myoglobin-cadmium telluride quantum dot conjugate was constructed using an artificial heme modified with a thiol moiety as a linker. Irradiation of the myoglobin-cadmium telluride conjugate generated the photoreduced ferrous myoglobin via an electron transfer from the photoexcited quantum dot, leading to the formation of CO-bound myoglobin under a CO atmosphere.

Supramolecular Linear Assemblies of Cytochrome b 562 Immobilized on a Gold Electrode

Linear assemblies of cytochrome b562 (cyt b562) containing a chemically-modified heme molecule on the protein surface were constructed by successive intermolecular heme–heme pocket interactions and then immobilized onto a gold electrode via a heme molecule anchored on the electrode. The accumulation of the cyt b562 units were confirmed by electrochemical analyses. The average number of proteins in each assembly was estimated to be about 6 units by quartz crystal microbalance and atomic force microscopy (AFM) analyses. The linear assemblies of the cyt b562 units were clearly visualized by AFM as a rod-like architecture with a vertical orientation to the electrode surface.

Fibrous supramolecular hemoprotein assemblies connected with synthetic heme dimer and apohemoprotein dimer.

Supramolecular hemoprotein assemblies via hemeheme pocket interaction were prepared by synthetic heme dimers containing a linker with charged amino acids and apohemoprotein disulfide dimers. The mixture of the negatively charged heme dimer and the apomyoglobin dimer provides heterotropic fibrous hemoprotein assemblies, which were characterized by size‐exclusion chromatography (SEC) and atomic force microscopy (AFM).