Yoshitaka Ueda

Role of Salt Bridge Formation in Antigen-Antibody Interaction ENTROPIC CONTRIBUTION TO THE COMPLEX BETWEEN HEN EGG WHITE LYSOZYME AND ITS MONOCLONAL ANTIBODY HyHEL10

For elucidation of the role of salt bridge formation in the antigen-antibody complex, the interaction between hen egg white lysozyme (HEL) and its monoclonal antibody HyHEL10, the structure of which has been well characterized and forms one salt bridge (Lys97 of HEL and Asp32 of HyHEL10 heavy chain variable region (VH)), was investigated. Asp32 of VH was substituted with Ala, Asn, or Glu by site-directed mutagenesis, and the interaction between HEL and the mutant fragments of the variable region of light chain was investigated by inhibition of the enzymatic activity of HEL and isothermal titration calorimetry. Inhibition assay indicated that these mutations lowered the inhibition only slightly. Thermodynamic study indicated that the negative enthalpic change in the interaction between each of the mutant variable regions of light chain and HEL was significantly increased, although the association constant was slightly decreased, suggesting that these mutations increased the entropy change upon antigen-antibody binding. These results indicate that the role of salt bridge formation in the HyHEL10-HEL interaction is to lower the entropic loss due to binding. In the mutant proteins, the numbers of residues that were perturbed structurally on binding increased, suggesting that the salt bridge suppresses excess structural movement of the antibody upon binding.

Expression of a Model Peptide of a Marine Mussel Adhesive Protein in Escherichia coli and Characterization of Its Structural and Functional Properties

An expression system for a chemically synthesized gene, encoding a model peptide of marine mussel adhesive protein, was constructed in Escherichia coli under regulation of the T7-promoter. The model peptide consisted of six repeats of the decapeptide AKPSYPPTYK. Although the product was expressed as an inclusion body, we were able to solubilize it successfully, using acetic acid. The higher-order structure of this model peptide was investigated using CD spectroscopy and NMR spectroscopy. Using the modified enzyme, mushroom tyrosinase, the tyrosine residue was hydroxy- lated to 3,4-dihydoxyphenylalanine (Dopa), and the resulting modified peptide was polymerized, solidified, and insolubilized spontaneously.

Effect of a rare leucine codon, TTA, on expression of a foreign gene in Streptomyces lividans

Streptomyces are bacteria with a very high chromosomal G+C composition (> 70 mol%) and extremely biased codon usage. In order to investigate the relationship between codon usage and gene expression in Streptomyces, we used ssi (Streptomyces subtilisin inhibitor) as a reporter gene and monitored its secretory expression in S. lividans. In consequence of alteration of the native codons of Leu, Lys and Ser of ssi to minor ones by site-directed mutagenesis, i.e., Leu79-Leu80: CTG-CTC to TTA-TTA, Lys89: AAG to AAA, Ser108-Ser109: TCG-AGC to TCT-TCT, respectively, the production of SSI was reduced remarkably in the case of TTA codons, while it was slightly increased in the case of AAA and almost the same in TCT codons. This conspicuous decrease found for Leu codon replacement was probably due to the low availability of intracellular tRNA(Leu) (UUA), a product of bldA which has been reported to be expressed only during the late stage of growth.

Long-range and short-range magnetic order in NaVGe2O6

Abstract The metaloxide pyroxene compound NaVGe 2 O 6 containing isolated edge-sharing VO 6 ( S =1) chains undergoes a transition into a long-range antiferromagnetic state at T N =16xa0K. The broad maximum in the temperature dependence of magnetic susceptibility at T M =26xa0K indicates the low-dimensional character of magnetic subsystem. Even though the antiferromagnetic ordering is accompanied by a sharp peak of specific heat, significant magnetic entropy is released above the Neel temperature.

Sequence of phase transitions in a quasi-one-dimensional β-Na0.33V2O5 compound with variable valence

The thermal properties—specific heat, thermal conductivity, and thermal expansion coefficients—of a single crystal of quasi-one-dimensional variable-valence β-Na0.33V2O5 compound were studied. With lowering temperature, it sequentially undergoes the structural (TS∼ 230 K), charge (TC∼ 136 K), and magnetic (TN∼ 22 K) phase transitions. The structural transition at TS, resulting in the ordering of the Na ions, and the charge ordering at TC, resulting in the charge redistribution over the positions of V ions, are accompanied by the anomalies in the temperature dependences of all the studied properties. The magnetic ordering at TN results in the appearance of the canted antiferromagnetic structure and manifests itself only in the anomaly in the temperature dependences of the thermal expansion coefficients.

Thermal properties of NaV2O5

Abstract Thermal properties of NaV 2 O 5 reflect the complex character of the phase transition at T C ∼34xa0K which includes the charge ordering, the lattice distortion and the spin gap formation in magnetic excitations spectrum. The specific heat shows sharp λ -type anomaly at T C , the heat conductivity strongly increases below T C , and the thermal expansion exhibits highly anisotropic behavior below T C .

Specific heat of Na1−xV2O5 single crystals

Temperature dependences of the specific heat C and the magnetic susceptibility χ of Na1−xV2O5 single crystals (x=0, 0.01, 0.02, 0.03, and 0.04) are studied. In NaV2O5, the transition to the spin-gap state (Tc=34 K) is accompanied by a sharp decrease in χ, while C exhibits a λ-shaped anomaly. At low temperatures, the specific heat of NaV2O5 is approximated by the sum of phonon ∼T3 and magnon ∼exp(−Δ/T) contributions, which makes it possible to estimate the Debye temperature ΘD=336 K and the gap in the magnetic excitation spectrum Δ=112 K. With the departure from stoichiometry, the anomalies observed in the behavior of χ and C are spread and shifted to lower temperatures. The low-temperature specific heat of nonstoichiometric samples is determined by the sum of phonon and magnon components and the contribution due to the presence of defects. The values of magnetic entropy characterizing the phase transitions in Na1−xV2O5 are calculated.

Specific heat and magnetic entropy of Na1−xV2O5

Abstract The specific heat of Na 1− x V 2 O 5 ( x =0, 0.01, 0.02, 0.03, 0.04) single crystalline samples was investigated in a temperature range 6–300xa0K. With deviation from stoichiometry the phase transition temperature and the energy gap in the magnetic excitation spectrum rapidly decrease. The specific heat anomaly becomes smaller and is not observed for x >0.03. The magnetic entropy released at the critical temperature in NaV 2 O 5 ∼7.7xa0J/molxa0K and decreases with x .