Effect of microwave heating time on the gel properties of chicken myofibrillar proteins and their formation mechanism

The present work was conducted to illustrate the mechanism of gel formation of myofibrillar proteins (MPs) under different microwave heating times. The results showed that the denaturation enthalpy (ΔH) of the MPs significantly decreased when the heating time increased from 3 to 9 s and then completely disappeared as the heating time progressed, indicating that the MPs gradually denatured and subsequently aggregated with increasing heating time, which was further verified by the changes in the secondary structure, electrophoretic bands, and gel properties (e.g., water holding capacity and textural profiles) of the MPs. Microstructural images indicated that the MP gel formed under 12 s had the most compact network, indicating that extended microwave heating time could induce quality deterioration of MP gels. Moreover, the hydrophobic forces, electrostatic forces, and disulphide bonds of the MPs gradually intensified with increasing microwave heating time, suggesting that both non-covalent and covalent bonds could promote molecular denaturation and subsequent aggregation of MPs. In addition, correlation analysis revealed that the changes in the molecular conformation of MPs induced by different microwave heating times could effectively regulate the formation of MP gels and their related properties.     

The Alkylquinolone Repertoire of Pseudomonas aeruginosa is Linked to Structural Flexibility of the FabH‐like 2‐Heptyl‐3‐hydroxy‐4(1H)‐quinolone (PQS) Biosynthesis Enzyme PqsBC

Pseudomonas aeruginosa is a bacterial pathogen that causes life‐threatening infections in immunocompromised patients. It produces a large armory of saturated and mono‐unsaturated 2‐alkyl‐4(1H)‐quinolones (AQs) and AQ N‐oxides (AQNOs) that serve as signaling molecules to control the production of virulence factors and that are involved in membrane vesicle formation and iron chelation; furthermore, they also have, for example, antibiotic properties. It has been shown that the β‐ketoacyl‐acyl‐carrier protein synthase III (FabH)‐like heterodimeric enzyme PqsBC catalyzes the last step in the biosynthesis of the most abundant AQ congener, 2‐heptyl‐4(1H)‐quinolone (HHQ), by condensing octanoyl‐coenzyme A (CoA) with 2‐aminobenzoylacetate (2‐ABA), but the basis for the large number of other AQs/AQNOs produced by P. aeruginosa is not known. Here, we demonstrate that PqsBC uses different medium‐chain acyl‐CoAs to produce various saturated AQs/AQNOs and that it also biosynthesizes mono‐unsaturated congeners. Further, we determined the structures of PqsBC in four different crystal forms at 1.5 to 2.7 Å resolution. Together with a previous report, the data reveal that PqsBC adopts open, intermediate, and closed conformations that alter the shape of the acyl‐binding cavity and explain the promiscuity of PqsBC. The different conformations also allow us to propose a model for structural transitions that accompany the catalytic cycle of PqsBC that might have broader implications for other FabH‐enzymes, for which such structural transitions have been postulated but have never been observed.     

The impact of recrystallisation on the freeze-thaw cycles of red seabream (Pagrus major) fillets

Recrystallisation often occurs in the freeze-thaw cycles and results in poor food quality. This study was undertaken to analyse the effects of recrystallisation on the changes of protein conformation and moisture migration within red seabream fillets after the freeze-thaw cycles. The UV second-derivative spectroscopy, intrinsic fluorescence measurement and Raman spectroscopy were employed to evaluate the protein conformational changes. The Low-field NMR spectra analysis was used to evaluate moisture migration. The results indicated that the freeze-thaw cycles altered the secondary and tertiary structure of proteins. It was noticed that interactions between water and protein molecules were decreased gradually and eventually induced the thermal instability of the myosin molecules. The immobilised water content declined and the free water content increased. There were significant destructions in fillet muscle microstructure. These observations unambiguously reflect how the recrystallisations affect the protein conformation and moisture migration patterns of red seabream fillets during freeze-thaw cycles.     

Conformation Analysis of GalNAc‐Appended Sugar Amino Acid Foldamers as Glycopeptide Mimics

Sugar amino acid (SAA)‐based foldamers with well‐defined secondary structures were appended with N‐acetylgalactosamine (GalNAc) sugars to access sequence‐defined, multidentate glycoconjugates with full control over number, spacing and position. Conformation analysis of these glycopeptides by extensive NMR spectroscopic studies revealed that the appended GalNAc units had a profound influence on the native conformational behaviour of the SAA foldamers. Whereas the 2,5‐cis glycoconjugate showed a helical structure in water, comprising of two consecutive 16‐membered hydrogen bonds, its 2,5‐trans congener displayed an unprecedented 16/10‐mixed turn structure not seen before in any glycopeptide foldamer.     

超高压调节酶催化功能及其作用机制

在酶学领域中,超高压和温度类似,作为一种物理学方法,可以用来调节酶催化功能,促使酶的构象发生变化。对超高压调节酶催化功能的原理、影响酶构象的作用机制,以及一些新型研究方法等进行了综述。展望了此项新技术的发展前景。     

Applying γ‐Substituted Prolines in the Foldon Peptide: Polarity Contradicts Preorganization

Rational choice of chemical modifications to proline residues allows the preorganization principle to be exploited for more stable assembly of the foldon domain as a tag for trimerization. With systematic knowledge of how chemical and steric variations of the ring substituents affect the relative stabilities of exo and endo puckers, the preorganization principle should then be usable in biotechnologically synthesized foldon mutants and applicable for protein tagging elsewhere.     

Macromolecular motions and hydrodynamic radius variation in dilute solutions under shear action

Understanding the dynamics of single polymer chains and rheological mechanism in dilute polymer solutions under shear stress is essential for fields such as the petroleum and food industries, biomedical materials and drug delivery. Here we present an experimental method for measuring the viscosity of polymer solutions and studying the variation of single polymer chain conformation and the mechanism of molecular motions according to the relationship between the intrinsic viscosity, [η], and the shear rate. Of striking interest is that we find that [η] changing with the shear rate presents three stages which may explain the nature of the viscoelastic performance of polymer solutions and the isolated molecular motions. The significance of these results is the finding of the polymer chain deformation to match the pore throat which has enormous potential implications in drug delivery, genetics and biomedicine © 2014 Society of Chemical Industry.     

Structural Consequences of the 1,2,3-Triazole as an Amide Bioisostere in Analogues of the Cystic Fibrosis Drugs VX-809 and VX-770

Although the 1,2,3-triazole is a commonly used amide bioisostere in medicinal chemistry, the structural implications of this replacement have not been fully studied. Employing X-ray crystallography and computational studies, we report the spatial and electronic consequences of replacing an amide with the triazole in analogues of cystic fibrosis drugs in the VX-770 and VX-809 series. Crystallographic analyses quantify subtle differences in the relative positions and conformational preferences of the R¹ and R² substituents attached to the amide and triazole bioisosteres. Computational studies derived from the X-ray data highlight the improved hydrogen bonding donor and acceptor capabilities of the amide in comparison to the triazole. This analysis of the spatial and electronic differences between the amide and 1,2,3-triazole will inform medicinal chemists as they consider using the triazole as an amide bioisostere.     

城市地铁盾构法区间隧道的设计

广州地铁二号线越秀公园一三元里区间盾构隧道已于2002年建成并投入试运营。阐述了该隧道的设计概况，主要内容包括：盾构隧道的线路拟合，衬砌环的构造形式，管片的结构设计和结构防水。总结了广州盾构隧道设计中的成功经验，并对当前盾构隧道设计中有关问题提出了建议。