Probing Protein Folding with Sequence-Reversed α-Helical Bundles

Recurrent protein folding motifs include various types of helical bundles formed by α-helices that supercoil around each other. While specific patterns of amino acid residues (heptad repeats) characterize the highly versatile folding motif of four-α-helical bundles, the significance of the polypeptide chain directionality is not sufficiently understood, although it determines sequence patterns, helical dipoles, and other parameters for the folding and oligomerization processes of bundles. To investigate directionality aspects in sequence-structure relationships, we reversed the amino acid sequences of two well-characterized, highly regular four-α-helical bundle proteins and studied the folding, oligomerization, and structural properties of the retro-proteins, using Circular Dichroism Spectroscopy (CD), Size Exclusion Chromatography combined with Multi-Angle Laser Light Scattering (SEC-MALS), and Small Angle X-ray Scattering (SAXS). The comparison of the parent proteins with their retro-counterparts reveals that while the α-helical character of the parents is affected to varying degrees by sequence reversal, the folding states, oligomerization propensities, structural stabilities, and shapes of the new molecules strongly depend on the characteristics of the heptad repeat patterns. The highest similarities between parent and retro-proteins are associated with the presence of uninterrupted heptad patterns in helical bundles sequences.     

变压器铁芯片自动叠装硬质合金级进模设计

分析了零件制造的工艺性。详细介绍了条料排样、模具结构的优化设计及一些技术难题的处理方法。     

一种折叠翼飞行器离筒性能分析

针对折叠翼飞行器发射离筒瞬间姿态变化及折叠翼机构展开性能问题,对影响飞行器离筒性能的主要因素进行了研究,对飞行器离筒过程进行了受力分析,分析了影响飞行器离筒性能的主要因素,建立了飞行器离筒过程理论模型和ADAMS仿真模型,对飞行器离筒过程中低头角变化、离筒时间、离筒速度、离筒最大应力、折叠翼机构展开时间和折叠翼展开同步性等参数进行了计算;对比分析了两种方法所得计算结果;分析了发射角对飞行器离筒过程中低头角和接触力的影响。研究结果表明,两种计算方法计算结果误差在5%以内,可以相互验证;水平发射时飞行器离筒低头角为0.49°、离筒时间为163 ms、离筒速度为14.12 m/s;随着发射角的增加飞行器离筒低头角减小,离筒过程最大冲击力减小;计算结果为飞行器发射性能提供了理论依据。     

“Z”型框架结构双向折叠控制爆破技术

采用双向折叠控制爆破技术拆除了一座“Z”型框架结构的体育场看台。为了降低爆破震动效应 ,采用了大时间差、空间差使看台逐跨逐层起爆 ,历时 4 80 0ms ,爆破效果达到了设计要求     

复杂环境下14层框剪楼房折叠拆除爆破

为了顺利拆除郑州市复杂环境下14层框剪结构的冰熊大厦,结合现场实际环境条件,选择了单向折叠拆除爆破方案.单向折叠爆破就是在待拆楼房1～3层和7～8层各设计1个爆破切口,并设计合理的爆破参数.同时,对电梯井、剪力墙局部进行预拆除,采用数码电子雷管延时起爆等技术,确保待拆楼房的倒塌方向和坍塌解体效果.通过筑减振坝和开挖减振...     

Is Protein Folding a Thermodynamically Unfavorable,Active, Energy-Dependent Process?

The prevailing current view of protein folding is the thermodynamic hypothesis, under which the native folded conformation of a protein corresponds to the global minimum of Gibbs free energy G. We question this concept and show that the empirical evidence behind the thermodynamic hypothesis of folding is far from strong. Furthermore, physical theory-based approaches to the prediction of protein folds and their folding pathways so far have invariably failed except for some very small proteins, despite decades of intensive theory development and the enormous increase of computer power. The recent spectacular successes in protein structure prediction owe to evolutionary modeling of amino acid sequence substitutions enhanced by deep learning methods, but even these breakthroughs provide no information on the protein folding mechanisms and pathways. We discuss an alternative view of protein folding, under which the native state of most proteins does not occupy the global free energy minimum, but rather, a local minimum on a fluctuating free energy landscape. We further argue that ΔG of folding is likely to be positive for the majority of proteins, which therefore fold into their native conformations only through interactions with the energy-dependent molecular machinery of living cells, in particular, the translation system and chaperones. Accordingly, protein folding should be modeled as it occurs in vivo, that is, as a non-equilibrium, active, energy-dependent process.     

柔性复合薄膜折叠损伤实验研究

对聚合物膜/预浸环氧碳纤维织物/聚合物膜这种三层薄膜材料(以下简称复合薄膜材料)的折叠损伤进行了试验研究.对未固化复合薄膜按一定折叠半径进行折叠,置于两平板间一定时间,然后展平加压加热固化并测试固化后复合薄膜材料的强度与刚度.结果表明,随着折叠半径的减少,材料的强度和等效拉伸模量下降.通过分析复合薄膜材料折叠损伤机理,确定了复合薄膜不发生损伤的最小折叠半径.另外,本研究还讨论了由于压缩屈曲导致的复合薄膜在拉伸中出现的分层破坏现象.     

制氢转化炉炉顶衬里结构的改造设计

通过制氢转化炉炉顶衬里结构改造两种设计方案的介绍,说明折叠式耐火陶瓷纤维模块用于转化炉炉顶衬里的优点.     

4种藏纸的抗老化性能初探

本实验分析了西藏雪拉藏纸、四川德格藏纸、囊谦嘎玛藏纸和囊谦黑色藏纸等4种藏纸的抗老化性能的差异性。分别对4种藏纸进行了紫外光老化前后纸张白度、耐折度、抗张力等指标的检测。结果表明,4种藏纸老化前各项指标相差较大,老化后上述指标均呈现下降趋势,西藏雪拉藏纸和四川德格藏纸的白度、耐折度、抗张力保留率好,具有相对良好的抗老化性。