The enzyme, cutinase from Saccharomonospora viridis AHK190 (Cut190), can hydrolyze the inner block of polyethylene terephthalate (PET). Cut190 has a unique feature that both its activity and thermal stability are increased upon Ca2+ binding. In consideration of the glass transition temperature of PET, which is between 60 and 65 °C, the increased activity and thermal stability are of great interest to apply for PET bio-recycling. Our previous mutational analysis showed that the S226P/R228S mutant (Cut190*) has a higher activity and thermal stability than those of the wild type. In this study, we analyzed the folding thermodynamics of the inactive mutant of Cut190*, Cut190*S176A, using circular dichroism and differential scanning calorimetry. The results show that the denaturation temperature increases from 54 to 71 °C due to the addition of 250 mM Ca2+, in a Ca2+ concentration-dependent manner. The increased thermal stability is mainly due to the increased enthalpy change, partially compensated by the increased entropy change. Based on the crystal structure of Cut190*S176A bound to Ca2+, molecular dynamics simulations were carried out to analyze the effects of Ca2+ on the structural dynamics, showing that the Ca2+-bound structure fluctuated less than the Ca2+-free structure. Structural analysis indicates that Ca2+ binding increases the intramolecular interactions of the enzyme, while decreasing its fluctuation, which are in good correlation with the experimental results of the folding thermodynamics.
Solubilization of hydrophilic saccharide chains into organic solvents has been attempted by incorporating saccharide-substituted styrene unit into polystyrene main chain. Lactose-, maltopentaose, and amylose-substituted styrene monomers were copolymerized with styrene. Resulting chloroform-soluble copolymers were characterized, and structural formation was investigated. Copolymers of lactose-substituted styrene and maltopentaose-substituted styrene with styrene were dissolved into chloroform. The chloroform-soluble polymers contained about 12 disaccharide lactose chains or 1.7 maltopentaose chains as the pendant groups in one polystyrene molecule. Chloroform-insoluble methyl orange was dissolved into chloroform with the help of chloroform-soluble polystyrene having some saccharide chains. On the other hand, when an amylose-substituted styrene unit was inserted in a polystyrene chain, the resulting polymer became insoluble into chloroform. Amylose polysaccharide of DPn = ∼24 was not dissolved into chloroform by this method. 相似文献
A two‐dimensional (2D) layered MgII coordination polymer (CP) with a high tolerance for H2O was designed, synthesised, and crystallographically characterised. The synthesis was achieved by the introduction of a flexible 2D layered structure composed of MgII ions and isonicotinate N‐oxide ligands. Owing to its high H2O tolerance, the obtained 2D layered structure has the flexibility to repeatedly adsorb a large amount of H2O associated with interlayer expansion and enable the removal of H2O from a H2O/2‐propanol mixed vapour. These results indicate that the CP could be an excellent dehydrating agent. 相似文献
The enantioselective formation of α‐aryloxy‐β‐keto esters is described for the first time. Lewis acid catalyzed enantioselective chlorination of β‐keto esters and subsequent SN2 reactions with phenols yielded α‐aryloxy‐β‐keto esters with up to 96 % ee. Favorskii rearrangement of α‐chloro‐β‐keto esters was also found to give 1,2‐diesters with slightly reduced enantiopurity. 相似文献
Weak-interaction responses of 11B were studied by measuring the 11B(3He, t) and 11B(p, p′) reactions. Obtained nuclear transition matrix elements B(GT), B(στ), and B(σ) were compared with the shell-model calculations. The shell-model calculations, which explained the isovector parts B(GT) and B(στ) reasonably well if the quenching factors of 0.5–0.7 were taken into account, did not describe the isoscalar part B(σ). 相似文献