Metal-ion-dependent GFP emission in vivo by combining a circularly permutated green fluorescent protein with an engineered metal-ion-binding coiled-coil

Coordination of metal ions significantly contributes to protein structures and functions. Here we constructed a fusion protein, consisting of a de novo designed, metal-ion-binding, trimeric coiled-coil and a circularly permutated green fluorescent protein (cpGFP), where the fluorescent emission from cpGFP was induced by metal ion coordination to the coiled-coil. A circularly permutated GFP, (191)cpGFP(190), was constructed by connecting the original N- and C-termini of GFP(UV) by a GGSGG linker and cleaving it between Asp(190) and Gly(191). The metal-ion-binding coiled-coil, IZ-HH, was designed to have three alpha-helical structures, with 12 His residues in the hydrophobic core of the coiled-coil structure. IZ-HH exhibited an unfolded structure, whereas it formed the trimeric coiled-coil structure in the presence of divalent metal ions, such as Cu(2+), Ni(2+), or Zn(2+). The fusion protein (191)cpGFP(190)-IZ-HH was constructed, in which (191)cpGFP(190) was inserted between the second and third alpha-helices of IZ-HH. Escherichia coli cells, expressing (191)cpGFP(190)-IZ-HH, exhibited strong fluorescence when the Cu(2+) and Zn(2+) ions were present in the medium, indicating that they passed through the cell membrane and induced the proper folding of the (191)cpGFP(190) domain. This strategy, in which protein function is regulated by a metal-ion-responsive coiled-coil, should be applicable to the design of various metal-ion-responsive, nonnatural proteins that work both in vitro and in vivo.     

Dynamical properties of photogenerated polarons in one-dimensional dimerized Mott Insulators

We study physical properties of photogenerated electron-lattice coupled states, polarons, in one-dimensional (1D) Peierls-Hubbard model with classical lattice distortion by means of the density matrix renormalization group method. The numerical results show novel midgap peaks in optical response spectra of polarons for large on-site Coulomb interaction U. These midgap peaks originate from charge-transfer excitations within the dimer in polarons.     

Cage Effects in Dimethylaminyl Radical Formation

The rate of decomposition of 1,1,4,4-tetramethyl-2-tetrazene (TMT) was measured in various unbranched alkanes of varying viscosities. The observed rate constant for the decomposition of TMT decreases with the viscosity of the solvent. A compensating change was found in the enthalpy and entropy of activation. It was also found that the decomposition of TMT occurs by the scission of only one N-N single bond and undergoes cage return in the alkanes by recombination of radicals.     

Solvent Effects on the Radical Copolymerizabilities of Styrene with p-Substituted N,N-Diethylcinnamamides and of p-Substituted Styrenes with Methyl Vinyl Sulfoxide

Radical copolymerizations of styrene (St) with p-substituted-N, N-diethylcinnamamides (I) and also of p-substituted styrenes (II) with methyl vinyl sulfoxide (MVSO) have been carried out in benzene, acetic acid or acetonitrile. The monomer reactivity ratios (r₁) were found to be affected by the solvents, p values obtained by using the modified Hammett equation, i. e., log(1/r₁) = ρσ + γ E_R, were also found to be altered by the solvents. The results are discussed in terms of the solvent effect in the transition state of the propagation reaction.     

Hydrogen Transfer Polymerization Mechanism of Acrylamide Induced by Propagating Polyacrolein Anion

In order to investigate the interaction between acrolein (AL) and acrylamide (AAm) on anionic copolymerization, the homopolymer-izabilities of AL in the presence of several p-substituted phenyl-acetamides such as p-nitroacetanilide, p-chloroacetanilide, acet-anilide, and p-methylacetanilide were investigated in tetrahydro-furan at 0°C using imidazole as an anionic catalyst. A linear co-relation was obtained by Hammett′ s equation as described by log R /R = 0.28σ. This result suggests that the homopolymeriz- P Po ability of AL is influenced by the structure of the amide compound. An increase of the additive propionamide (PAm) on the homopolym-erization of AL induced by the pyridine-water initiation system increased the polymerization rate R; however, it decreased the intrinsic viscosity [η] of poly-AL. From the measurement of infrared spectroscopy and elementary analysis, the presence of a chain transfer reaction between the poly-AL anion and PAm was found. These results support the presence of interaction between AL and AAm derivatives in the copolymerization system.