Reconstitution of pilus assembly reveals a bacterial outer membrane catalyst

Type 1 pili from uropathogenic Escherichia coli are a prototype of adhesive surface organelles assembled and secreted by the conserved chaperone/usher pathway. We reconstituted type 1 pilus biogenesis from purified pilus proteins. The usher FimD acted as a catalyst to accelerate the ordered assembly of protein subunits independently of cellular energy. Its activity was highly dependent on the adhesin subunit FimH, which triggered the conversion of FimD into a high-efficiency assembly catalyst. Furthermore, a simple kinetic model adequately rationalized usher-catalyzed pilus assembly in vivo. Our results contribute to a mechanistic understanding of protein-catalyzed biogenesis of supramolecular protein complexes at the bacterial outer cell membrane.     

Structure and Properties of Crystalline Polymers: Supramolecular structure is complex, can be controlled, and influences mechanical properties

Through control of the crystallization process many polymers can be made to exhibit a broad spectrum of structural possibilities, ranging from a state of high disorder to one of high order. Emphasis has been placed on bulk-crystallized polymers which normally fall near the center of this spectrum. This was done in part because polymers are most commonly fabricated in this manner, and also because the amount of attention given in recent years to crystals grown from dilute solution has tended to obscure important aspects of the structure of bulk-crystallized polymers. Differences in the structure of the interlamellar regions account most reasonably for many of the variations in mechanical properties that crystalline polymers can be made to display. The interlamellar amorphous model, proposed here as a structural model for bulk-crystallized polymers, largely neglects the lamellae themselves, because so little is known about the structure of the lamellae of bulk-crystallized polymers and how variations in lamellar structure can affect properties. This model is intended, therefore, as both a working hypothesis to aid further investigation and as an outline to be filled in as more is learned about the supramolecular structure of crystalline polymers (31).     

Forming supramolecular networks from nanoscale rods in binary, phase-separating mixtures

Simulations show that when low-volume fractions of nanoscale rods are immersed in a binary, phase-separating blend, the rods self-assemble into needle-like, percolating networks. The interconnected network arises through the dynamic interplay of phase-separation between the fluids, through preferential adsorption of the minority component onto the mobile rods, and through rod-rod repulsion. Such cooperative effects provide a means of manipulating the motion of nanoscopic objects and directing their association into supramolecular structures. Increasing the rod concentration beyond the effective percolation threshold drives the system to self-assemble into a lamellar morphology, with layers of wetted rods alternating with layers of the majority-component fluid. This approach can potentially yield organic/inorganic composites that are ordered on nanometer scales and exhibit electrical or structural integrity.     

Allosteric supramolecular triple-layer catalysts

Allosteric regulation of organometallic catalysts could allow for greater control over reactions. We report an allosteric supramolecular structure in which a monometallic catalytic site has been buried in the middle layer of a triple-layer complex. Small molecules and elemental anions can open and close this complex and reversibly expose and conceal the catalytic center. The ring-opening polymerization of ε-caprolactone can be turned on by the in situ opening of the triple-layer complex and then completely turned off by reforming it through the abstraction of Cl(-), the allosteric effector agent, without appreciable loss of catalytic activity. This process can regulate the molecular weights of the resulting polymers.     

Excimers and exciplexes of conjugated polymers

Observations of intermolecular excimers in several pi-conjugated polymers and exciplexes of these polymers with tris(p-tolyl) amine are reported. It is shown that the luminescence of conjugated polymer thin films originates from excimer emission and that the generally low quantum yield is the result of self-quenching. Thus, in sufficiently dilute solution, the "single-chain" emission has a quantum yield of unity. Exciplex luminescence and exciplex-mediated charge photogeneration have much higher quantum yields than the excimer-mediated photophysical processes. These results provide a basis for understanding and controlling the photophysics of conjugated polymers in terms of supramolecular structure and morphology.     

Involvement of RNA in the synthesis of proteins

We can now have considerable confidence that the broad features of protein synthesis are understood. The involvement of RNA is very much more complicated than was imagined in 1953. There is not one functional RNA. Instead, protein synthesis demands the ordered interaction of three classes of RNA-ribosomal, soluble, and messenger. Many important questions, however, remain unanswered. For instance, there is no theoretical framework for the ribosomal subunits, nor for that matter, do we understand the functional significance of ribosomal RNA. Most satisfying is the realization that all the steps in protein replication will be shown to involve well-understood chemical forces. As yet we do not know all the details. For example, are the DNA base pairs involved in messenger RNA selection of the corresponding amino-acyl-sRNA? With luck, this will soon be known. We can thus have every expectation that future progress in understanding selective protein synthesis (and its consequences for embryology) will have a similarly well-defined and, when understood, easy-to-comprehend chemical basis (62).     

小麦籽粒Waxy蛋白亚基动态表达规律的研究

[目的]对新疆自育的4个春小麦品种新春8号、新春9与、新春11号和新春14号的Waxy蛋白亚基在籽粒灌浆过程中的动态表达进行分析,研究扬花期后籽粒贮藏蛋白中Waxy蛋白亚基的动态累积规律,为小麦淀粉的品质改良提供理论依据.[方法]利用Waxy蛋白亚基特异分子标记,通过SDS-PAGE电泳进行Waxy蛋白亚基的检测.[结果]4个品种Waxy蛋白亚基的组成不尽相同,新春8号和新春11号Waxy蛋白3个亚基都存在,而新春9号和新春14号为Wx-B1亚基的缺失类型.新春8号亚基出现的时期较晚,花后20 d开始检测到;新春14号Wx-D1亚基的表达要晚于Wx-A1亚基;新春9号和11号亚基于花后15 d检测到,但在籽粒灌浆各时期表达强弱也不尽一致.[结论]Waxy蛋白亚基形成具有时间性,且各亚基在籽粒灌浆过程中的表达规律品种间也不尽一致.     

聚丙稀酰胺高吸附树脂与重金属离子的相互作用

为探究高吸附树脂对重金属离子的吸附能力,用聚丙烯酰胺高吸附树脂对Cu(NO3)2、Pb(NO3)2标准溶液进行吸附,研究高吸附树脂与Cu2+、Pb2+的相互作用关系。结果表明:高吸附树脂吸水倍率随Cu2+、Pb2+浓度增大而显著减小,两者之间存在显著幂函数关系。离子吸附量随Cu2+、Pb2+浓度增大而显著增大,吸附平衡时Cu2+、Pb2+的最大吸附量分别为131.72、242.68 mg/g,高吸附树脂吸附过程符合Freundlich等温吸附方程。高吸附树脂对Cu2+、Pb2+的吸附量随时间增加而增大,吸附速率逐渐减小,吸附动力学可用准二级动力学方程描述。相同质量浓度下,高吸附树脂对Pb2+的吸附量和吸附速率均大于Cu2+。吸水凝胶在去离子水中和硝酸溶液中解吸很快,大约1 h后达到平衡,高吸附树脂在去离子水中解吸率不高,但在1 mol/L HNO3溶液中Cu2+、Pb2+解吸率均大于85%。高吸附树脂3次重复吸附后,Cu2+、Pb2+平衡吸附量分别为第1次吸附量的75.36%和78.12%,重复吸附性能良好。研究结果可为高吸附树脂应用于含有重金属的污水处理和土壤修复提供参考。      

Supramolecular Materials: Self-Organized Nanostructures

Miniaturized triblock copolymers have been found to self-assemble into nanostructures that are highly regular in size and shape. Mushroom-shaped supramolecular structures of about 200 kilodaltons form by crystallization of the chemically identical blocks and self-organize into films containing 100 or more layers stacked in a polar arrangement. The polar supramolecular material exhibits spontaneous second-harmonic generation from infrared to green photons and has an adhesive tape-like character with nonadhesive-hydrophobic and hydrophilic-sticky opposite surfaces. The films also have reasonable shear strength and adhere tenaciously to glass surfaces on one side only. The regular and finite size of the supramolecular units is believed to be mediated by repulsive forces among some of the segments in the triblock molecules. A large diversity of multifunctional materials could be formed from regular supramolecular units weighing hundreds of kilodaltons.     

Synthetic genetic polymers capable of heredity and evolution

Genetic information storage and processing rely on just two polymers, DNA and RNA, yet whether their role reflects evolutionary history or fundamental functional constraints is currently unknown. With the use of polymerase evolution and design, we show that genetic information can be stored in and recovered from six alternative genetic polymers based on simple nucleic acid architectures not found in nature [xeno-nucleic acids (XNAs)]. We also select XNA aptamers, which bind their targets with high affinity and specificity, demonstrating that beyond heredity, specific XNAs have the capacity for Darwinian evolution and folding into defined structures. Thus, heredity and evolution, two hallmarks of life, are not limited to DNA and RNA but are likely to be emergent properties of polymers capable of information storage.     

小麦优质亚基和抗白粉病Pm4a基因聚合体的PCR鉴定

为选育优质、高产、抗病的小麦品系（种）,以含1Dx5+1Dy10亚基的宁春4号和含Pm4a抗白粉病基因的扬麦19为亲本,从其杂交F2后代 1/3～1/2粒种子提取DNA,并利用1Dx5亚基和Pm4a基因的特异标记对其进行PCR鉴定。结果表明：在100粒F2代种子中,有51粒种子被鉴定为1Dx5亚基和Pm4a基因聚合体。该试验采用的PCR鉴定,克服了SDS PAGE电泳耗时多、容易对迁移率相近亚基做出误判的缺点,同时也摆脱了白粉病大田和温室鉴定时受气候条件和农时的限制,大大提高了鉴定的效率和准确性。对中选的聚合体做进一步鉴定,有望选出农艺性状好、产量高、品质优、抗白粉病的小麦品系。     

Storage of methane and freon by interstitial van der Waals confinement

A known host-guest assembly, organized only by means of relatively weak dispersive forces, exhibits hitherto unappreciated thermal stability. The hexagonal close-packed arrangement of calix[4]arene contains lattice voids that can occlude small, highly volatile molecules. This host-guest system can be exploited to retain a range of freons, as well as methane, not only well above their normal boiling points, but also at relatively high temperatures and low pressures. The usually overlooked van der Waals interactions in organic crystals can indeed be used in a highly stable supramolecular system for gas storage.     

不同土壤水分条件下保水剂对小麦幼苗生理特性的影响

采用盆栽试验研究了不同土壤水分条件、不同用量保水剂对小麦幼苗生理特性的影响。结果表明,在严重干旱处理下,保水剂对小麦幼苗产生抑制作用,随保水剂用量增加,小麦幼苗的叶片相对含水量、叶绿素含量、根系活力呈下降趋势,叶片饱和亏缺、可溶性糖含量、脯氨酸含量、丙二醛含量呈上升趋势;在中等干旱处理下,保水剂作用效果最佳,对小麦幼苗的生理代谢有明显的促进作用。不同用量保水剂在不同指标间效果差异表现不同。在充足水分处理下,保水剂对小麦幼苗的生理代谢作用低于中等干旱处理。中度干旱下施用保水剂效果最明显,并以60 kg/hm2用量为最佳。     

氮肥对扬麦13籽粒GMP和蛋白质含量调节效应

以“2＋12”亚基组合小麦品种扬麦13为供试材料,研究了氮素营养对小麦籽粒高分子量谷蛋白亚基（HMW-GS）的积累量、谷蛋白大聚合体（GMP）含量及蛋白质含量的调节效应。结果表明：1）氮肥用量和运筹比例不改变小麦品种HMW-GS组成,但可以提高HMW-GS各位点的亚基积累量,提高亚基的总积累量,氮肥用量对小麦籽粒蛋白质的调控可能是通过亚基来发挥效应的;2）随着氮肥用量的增加,小麦籽粒蛋白质HMW-GS积累量、GMP含量、蛋白质及干湿面筋含量增加;3）不同氮肥运筹比例改变籽粒蛋白质HMW-GS积累量,随氮肥后移籽粒GMP含量、蛋白质含量增加。     

Complexity and climate

The climate that we experience results from both ordered forcing and chaotic behavior; the result is a system with characteristics of each. In forecasting prospective climate changes for the next century, the focus has been on the ordered system's responses to anthropogenic forcing. The chaotic component may be much harder to predict, but at this point it is not known how important it will be.     

聚合物分子尺寸大小及其与岩石孔喉尺寸配伍关系的试验研究

为了探索和验证聚合物分子尺寸与岩石孔喉尺寸的配伍关系,以河南油田东部老油区稀油油田为例,应用数学方法、微孔滤膜过滤方法和动态光散射方法,对开展聚合物驱条件下拟使用的聚合物的分子尺寸进行试验测定,得到了双河油田不同渗透率岩石能够匹配的聚合物分子量。     

聚合物分子尺寸大小及其与岩石孔喉尺寸配伍关系的试验研究

为了探索和验证聚合物分子尺寸与岩石孔喉尺寸的配伍关系,以河南油田东部老油区稀油油田为例,应用数学方法、微孔滤膜过滤方法和动态光散射方法,对开展聚合物驱条件下拟使用的聚合物的分子尺寸进行试验测定,得到了双河油田不同渗透率岩石能够匹配的聚合物分子量。     

小麦HMW-GS毛细管电泳标准图谱的构建

用毛细管电泳技术对普通小麦品种Glu-1位点高分子量谷蛋白亚基变异进行分析,探讨该技术对高分子量谷蛋白亚基分离的分辨率和重复性,并构建15个不同常见亚基的标准图谱,试验结果增加1Dx3、1Dx4、1Bx13、1Bx14、1By15、1By16六个亚基的标准出峰时间并进行排序。对毛细管电泳图谱与SDS-PAGE进行比较。结果表明,毛细管电泳的出峰顺序与SDS-PAGE略有不同,使用该技术能简便迅速鉴定小麦高分子量谷蛋白优质亚基,比SDS-PAGE鉴定结果更为快捷灵敏,能够高效快速测定大量不同品种的高分子量谷蛋白亚基。     

木质纤维细胞壁大分子取向研究进展

木质纤维细胞壁主要是由纤维素、半纤维素以及具网络结构的木质素交联形成的高度有序的三维立体结构,是植物最基本的力学承载单元。本文首先概述了国内外有关木质纤维细胞壁中纤维素、半纤维素和木质素3种结构大分子的模量、强度等微力学特性,其次就纤维素?半纤维素、纤维素?木质素以及半纤维素?木质素大分子间的交联结构、分子间的有序组装规律进行了总结。在此基础上,对比分析了光学显微成像、电子显微成像、原子力显微成像、显微红外光谱、线偏振显微拉曼光谱、和频振动光谱以及同步辐射X射线衍/射技术在细胞壁大分子取向研究过程中的异同点。重点讨论通过分子光谱化学成像技术揭示的木质纤维原料不同类型细胞以及同一类型细胞不同亚层中3种结构大分子取向排列规律。最后,展望了木质纤维原料大分子取向研究可能的发展趋势:系统表征木质纤维细胞壁纤维素超分子结构、三大组分间连接键类型、纤维素构象对半纤维素糖苷键及木质素芳香环有序组装的影响机制;在纳米尺度揭示木质纤维发育过程中,各类细胞壁中纤维素纤丝聚集体结构、取向和微力学变化规律;在细胞壁水平非破坏性地对木质纤维大分子取向进行三维立体成像和定量研究;基于分子结构表征、分子模拟和三维成像研究结果实现针叶、阔叶及禾本科植物纤维细胞壁骨架模型的构建。      

Iodination in relation to thyroglobulin maturation and subunit aggregation

Noniodinated subunits of thyroglobulin can aggregate, but iodination of the aggregate is required for its stabilization (maturation). Rat-thyroid slices incorporate amino acids into subunits, but cannot form mature thyroglobulin from the newly synthesized subunits. This defect leads to an accumulation of 16S and 12S proteins, although the preexisting thyroglobulin is 19S. Accumulation of 16S and 12S proteins can be produced in rat thyroids by the administration to the animals of a thiocarbamide derivative, methimazole. Upon withdrawal of methimazole, iodination of the 16S and 12S proteins proceeds, and 19S protein appears.