Identification of the Primary Factors Determining the Specificity of Human VKORC1 Recognition by Thioredoxin-Fold Proteins

Redox (reduction–oxidation) reactions control many important biological processes in all organisms, both prokaryotes and eukaryotes. This reaction is usually accomplished by canonical disulphide-based pathways involving a donor enzyme that reduces the oxidised cysteine residues of a target protein, resulting in the cleavage of its disulphide bonds. Focusing on human vitamin K epoxide reductase (hVKORC1) as a target and on four redoxins (protein disulphide isomerase (PDI), endoplasmic reticulum oxidoreductase (ERp18), thioredoxin-related transmembrane protein 1 (Tmx1) and thioredoxin-related transmembrane protein 4 (Tmx4)) as the most probable reducers of VKORC1, a comparative in-silico analysis that concentrates on the similarity and divergence of redoxins in their sequence, secondary and tertiary structure, dynamics, intraprotein interactions and composition of the surface exposed to the target is provided. Similarly, hVKORC1 is analysed in its native state, where two pairs of cysteine residues are covalently linked, forming two disulphide bridges, as a target for Trx-fold proteins. Such analysis is used to derive the putative recognition/binding sites on each isolated protein, and PDI is suggested as the most probable hVKORC1 partner. By probing the alternative orientation of PDI with respect to hVKORC1, the functionally related noncovalent complex formed by hVKORC1 and PDI was found, which is proposed to be a first precursor to probe thiol–disulphide exchange reactions between PDI and hVKORC1.     

Turncoat Polypeptides: We Adapt to Our Environment

A common interpretation of Anfinsen's hypothesis states that one amino acid sequence should fold into a single, native, ordered state, or a highly similar set thereof, coinciding with the global minimum in the folding-energy landscape, which, in turn, is responsible for the function of the protein. However, this classical view is challenged by many proteins and peptide sequences, which can adopt exchangeable, significantly dissimilar conformations that even fulfill different biological roles. The similarities and differences of concepts related to these proteins, mainly chameleon sequences, metamorphic proteins, and switch peptides, which are all denoted herein “turncoat” polypeptides, are reviewed. As well as adding a twist to the conventional view of protein folding, the lack of structural definition adds clear versatility to the activity of proteins and can be used as a tool for protein design and further application in biotechnology and biomedicine.     

Insights into Protein Stability in Cell Lysate by 19F NMR Spectroscopy

In living organisms, protein folding and function take place in an inhomogeneous, highly crowded environment possessing a concentration of diverse macromolecules of up to 400 g/L. It has been shown that the intracellular environment has a pronounced effect on the stability, dynamics and function of the protein under study, and has for this reason to be considered. However, most protein studies neglect the presence of these macromolecules. Consequently, we probe here the overall thermodynamic stability of cold shock protein B from Bacillus subtilis (BsCspB) in cell lysate. We found that an increase in cell lysate concentration causes a monotonic increase in the thermodynamic stability of BsCspB. This result strongly underlines the importance of considering the biological environment when inherent protein parameters are quantitatively determined. Moreover, we demonstrate that targeted application of ¹⁹F NMR spectroscopy operates as an ideal tool for protein studies performed in complex cellular surroundings.     

Synthesis of carbon nanomaterials for dye‐sensitized solar cells

In this paper, it was demonstrated that Na₂O can react with CO to produce carbon nanofibers at 500 °C and carbon nanosheets at 550 °C. Furthermore, the nanosheets exhibited excellent performance as a counter electrode for a dye‐sensitized solar cell (DSSC), leading to a high power conversion efficiency of 7.57%. The efficiency is larger than that (4.72%) of a DSSC with the carbon nanofiber counter electrode and even comparable with that of an expensive Pt‐based DSSC. Copyright © 2015 John Wiley & Sons, Ltd.     

Cellular Disulfide Bond Formation in Bioactive Peptides and Proteins

Bioactive peptides play important roles in metabolic regulation and modulation and many are used as therapeutics. These peptides often possess disulfide bonds, which are important for their structure, function and stability. A systematic network of enzymes—a disulfide bond generating enzyme, a disulfide bond donor enzyme and a redox cofactor—that function inside the cell dictates the formation and maintenance of disulfide bonds. The main pathways that catalyze disulfide bond formation in peptides and proteins in prokaryotes and eukaryotes are remarkably similar and share several mechanistic features. This review summarizes the formation of disulfide bonds in peptides and proteins by cellular and recombinant machinery.     

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.     

Honeycomb-like bio-based carbon framework decorated with ternary tantalum-based compounds as efficient and durable electrocatalysts for triiodide reduction reaction

Finding an inexpensive and effective clean energy electrocatalyst is highly important for the new generation of photovoltaic devices. Herein, we report a facile and universal in situ co-precipitation strategy to load three novel tantalum-based compounds (NiTa₂O₆, MnTa₂O₆, and AlTaO₄) on honeycomb-like bio-based carbon (HBC) frameworks. The HBC framework with unique honeycomb-like network structure serves as a support material in nanohybrids that can provide rich surface active sites and rapid electron transport channels for triiodide reduction reaction. The adoption of widely available and abundant biomass-derived carbon into tantalum-based compounds markedly boosts electrocatalytic properties of nanohybrids and exhibits robust corrosion resistance because nanohybrids adequately utilize the synergistic effects of different components. The photovoltaic devices fabricated with NiTa₂O₆/HBC, MnTa₂O₆/HBC, and AlTaO₄/HBC counter electrode catalysts demonstrate the brilliant power conversion efficiency (PCE) of 7.09%, 7.39%, and 7.86%, respectively, outperforming the Pt-based cells (6.80%). This work offers a strategy for the further rational design of efficient, inexpensive, and durable electrocatalysts for advanced energy technology applications.     

High-performance counter electrode based on nitrogen-doped porous carbon nanoribbons for quantum dot-sensitized solar cells

Nitrogen-doped porous carbon nanoribbons (NPCNs) are facilely prepared by carbonization of polypyrrole (PPy) nanotubes followed by a chemical activation process. NPCN counter electrodes are subsequently fabricated by depositing NPCNs onto Ti mesh for quantum dot-sensitized solar cells (QDSCs). Electrochemical tests are carried out to evaluate the electrocatalytic performance of obtained NPCN electrode. The data of electrochemical tests suggest that the NPCN electrode has a superior electrocatalytic ability towards polysulfide (S₂²⁻/S²⁻) electrolyte regeneration reaction and displays a high stability in polysulfide electrolyte. The excellent electrocatalytic performance of NPCN electrode can be ascribed to their large surface area, 2D porous nanoribbon morphology, and nitrogen atom doping, which provides abundant electrocatalytic active sites and facilitates the electrolyte diffusion. Consequently, a power conversion efficiency of 3.27% is obtained by using NPCN electrode as the counter electrode for QDSC. This efficiency is close to the QDSC assembled with commonly used PbS electrode (4.0%).     

变截面Z型折叠机翼振动特性的有限元与实验分析

Z型变截面折叠机翼作为一种可变体机翼结构,不同的折叠角对机翼稳定性有着重要的影响,因此研究不同折叠角度下的特性参数对机翼动态稳定性有着重要的意义.本文首先设计加工了Z型变截面可折叠机翼结构的实验模型,通过建立与实验模型相匹配的有限元模型,仿真得到不同折叠角度下机翼的前5阶固有频率和振型,针对不同折叠角度下机翼的固有特性,通过扫频实验得到机翼前5阶固有频率和模态振型,以及横向外激励作用下三段翼的频响曲线,对比分析有限元仿真与实验结果,验证结果的可靠性,这将对机翼结构设计以及特性参数的选取提供参考依据.