天然纤维素超显微结构的扫描隧道显微镜研究

用扫描隧道显微镜（ＳＴＭ）对天然纤维素脱脂棉的超显微结构进行了研究,结果表明用ＳＴＭ可直接观察到脱脂棉的微纤丝和基原纤丝。另外,还直接观察到了脱脂棉中纤维素分子的结晶区和非结晶区以及分叉状结构,从而表明棉花纤维素是一种结晶不完全的多聚物。     

低O2高CO2性肺动脉高压大鼠血浆内皮素和肺细小动脉超微？…

为探讨低Ｏ２高ＣＯ２性肺动脉高压形成的机制,对血浆内皮素（ＥＴ）和肺细小动脉超微结构改变进行研究。应用低Ｏ２高ＣＯ２性肺动脉高压大鼠模型,观察了不同ＥＴ浓度时肺细小动脉超微结构改变。实验组①ＥＴ浓度明显升高,②肺细小动脉内皮细胞（ＥＣ）水肿,内质网扩张,内皮下水肿明显,内膜增厚;③肺细小动脉中膜平滑肌细胞（ＳＭＣ）竖立,微丝束增多,ＳＭＣ数目增多,细胞面积增大;④外膜纤维母细胞（ＦＩＢ）增生,胶原     

应用原子力显微镜对玉米染色质纤丝及染色体骨架的研究(英文)

应用原子力显微镜对经化学方法预处理的玉米染色体超微结构进行了研究。原子力显微镜观察的结果揭示,经30%醋酸处理的玉米染色体表面呈现出不均一的颗粒状结构。当缩小扫描范围后,在染色体表面发现直径分别为30和100 nm的两种染色质纤丝。100 nm的染色质纤丝由30 nm染色质纤丝螺旋缠绕而成。在经25%胰酶处理的玉米染色体上发现了两种类似的螺旋状染色质纤丝结构,其直径分别为30和100～150 nm。较细的染色质纤丝螺旋缠绕成较粗的纤丝,进而构成整个染色体。经低离子浓度溶液抽提,用原子力显微镜观察到了玉米染色体的染色体骨架结构。这种染色体骨架呈不规则的纤维网状,这些网状纤维在染色体中部显得较为紧密,在染色体的边缘则显得较松散。这一结果暗示染色体是由不同级别的染色质纤丝螺旋缠绕构成,为染色体的多级螺旋结构假说提供了新的证据。同时发现染色体骨架并不是呈轴样的结构存在,而是保留了染色体的基本形态,这种骨架形状也许是由分散在染色体中的染色体骨架蛋白在低离子浓度溶液抽提的过程中凝缩形成的。     

低O_2高CO_2性肺动脉高压大鼠血浆内皮素和肺细小动脉超微结构的研究

为探讨低Ｏ２高ＣＯ２性肺动脉高压形成的机制,对血浆内皮素（ＥＴ）和肺细小动脉超微结构改变进行研究。应用低Ｏ２高ＣＯ２性肺动脉高压大鼠模型,观察了不同ＥＴ浓度时肺细小动脉超微结构改变。实验组①ＥＴ浓度明显升高,②肺细小动脉内皮细胞（ＥＣ）水肿,内质网扩张,内皮下水肿明显,内膜增厚;③肺细小动脉中膜平滑肌细胞（ＳＭＣ）竖立,微丝束增多,ＳＭＣ数目增多,细胞面积增大;④外膜纤维母细胞（ＦＩＢ）增生,胶原纤维密集。结果表明低Ｏ２高ＣＯ２引起的血浆ＥＴ增高,可致肺动脉内膜增厚、平滑肌细胞和纤维母细胞增生,可能是肺动脉高压形成的重要机制之一。     

二甲基亚砜对黑麦根尖分生组织细胞超显微结构的影响

黑麦根尖在原位用二甲垫亚砜(DMSO)处理之后,电子显微镜下观察发现根尖分生组织区细胞的细胞核和细胞质内也出现类似微丝的微纤丝结构。与我们以前在经DMSO处理过的黑麦小孢子母细胞核中所看到的微纤丝结构一样,根尖分生组织区细胞中微纤丝结构直径也约为6—9 nm,许多根微纤丝平行地排列在一起构成微纤丝束,本研究提示DMSO对于植物的体细胞和小孢子母细胞具有相同的生物学效应。也提示黑麦根尖分生组织细胞和小孢子母细胞的核基质可能具有相似的组成。     

《Molecular Plant》文章中文摘要

题目：植物细胞壁基质（matrix）多糖的生物合成（综述） 摘要：伸长中的植物细胞的细胞壁主要由纤维素微纤丝和基质多糖（半纤维素和果胶）以及少量结构蛋白和酶蛋白组成。基质多糖在高尔基体中合成,通过胞吐作用输送到细胞壁,并与纤维素微纤丝相嵌。纤维素微纤丝在细胞膜上合成并直接沉积到细胞壁。已知在生长素诱导的伸长细胞中,高尔基体中存在多糖链合成,然而直到最近才鉴定出合成多糖链酶的相关基因。在基因鉴定研究中,     

齐口裂腹鱼消化道粘膜上皮的扫描电镜观察

齐口裂腹鱼消化道粘膜上皮的扫描电镜观察方静,谢林,李逊,周毅（四川农业大学,雅安６２５０１４）关键词齐口裂腹鱼、微脊、微绒毛、杯状细胞、扫描电镜ＳＣＡＮＮＩＮＧＥＬＥＣＴＲＯＮＭＩＣＲＯＳＣＯＰＩＣＳＴＵＤＹＯＦＤＩＧＥＳＴＩＶＥＴＲＡＣＴＯＦＳＣＨ...     

油蒿和籽蒿种子化学组成的研究

油蒿和籽蒿种子化学组成的研究鲁作民（中国科学院兰州沙漠研究所,兰州７３００００）ＳＴＵＤＩＥＳＯＮＣＨＥＭＩＣＡＬＣＯＭＰＯＳＩＴＩＯＮＳＩＮＳＥＥＤＳＯＦＡＲＴＥＭＩＳＩＡＯＲＤＯＳＩＣＡＡＮＤＡ．ＳＰＨＡＥＲＯＣＥＰＨＡＬＡ￥ＬｕＺｕｏ－ｍｉｎ（...     

抗寒剂在棉花防寒育苗上的应用试验效果

抗寒剂在棉花防寒育苗上的应用试验效果崔应国,汪元喜,梅金龙（安徽省铜陵县农科所,棉科所,２４４１００）ＥＸＰＥＲＩＭＥＮＴＡＬＥＦＦＥＣＴＳＯＦＴＨＥＣＯＬＤ－ＲＥＳＩＳＴＥＲＦＯＲＩＮＣＲＥＡＳＩＮＧＣＯＬＤ－ＲＥＳＩＳＴＡＮＣＥＯＦＣＯＴＴＯＮＳ...     

日本血吸虫26kD抗原基因在BCG中的表达

研究了外源基因日本血吸虫２６ｋＤ抗原（Ｓｊ２６ＧＳＴ）在卡介苗（ｂａｃｉｌｕｓＣａｌｍｅｔｅ－Ｇｕｅｒｉｎ,ＢＣＧ）、耻垢分枝杆菌（Ｍ．ｓｍｅｇｍａｔｉｓ）和大肠杆菌（Ｅ．ｃｏｌｉ）中的表达．运用重组ＤＮＡ和聚合酶链反应（ＰＣＲ）等分子生物学技术,以表达Ｓｊ２６ＧＳＴ的Ｅ．ｃｏｌｉｐＧＥＸ衍生质粒为模板,经ＰＣＲ得到编码Ｓｊ２６ＧＳＴ的全长ｃＤＮＡ片段．将其按正确的阅读框顺序,克隆到人结核杆菌热休克蛋白（ｈｅａｔｓｈｏｃｋｐｒｏｔｅｉｎ,ＨＳＰ）７０的启动子下游,再将ＨＳＰ７０启动子和Ｓｊ２６ＧＳＴ基因一起亚克隆到Ｅ．ｃｏｌｉ－分枝杆菌穿梭质粒ｐＢＣＧ－２０００中,得到Ｅ．ｃｏｌｉ－分枝杆菌穿梭表达质粒ｐＢＣＧ－Ｓｊ２６．ｐＢＣＧ－Ｓｊ２６电转化入ＢＣＧ和Ｍ．ｓｍｅｇｍａｔｉｓｍｃ２１５５中表达Ｓｊ２６ＧＳＴ抗原,所表达的天然重组Ｓｊ２６ＧＳＴ（ｒＳｊ２６ＧＳＴ）为可溶性蛋白,在ＳＤＳ－ＰＡＧＥ上分子量为２６ｋＤ处可见明显的表达蛋白带．其表达量分别占ＢＣＧ和Ｍ．ｓｍｅｇｍａｔｉｓ菌体总蛋白的１５％和１０％．可见,Ｓｊ２６ＧＳＴ基因能在ＢＣＧ中高效表达．     

Amyloid-like fibril formation of co-chaperonin GroES: nucleation and extension prefer different degrees of molecular compactness

The molecular chaperone GroES, together with GroEL from Escherichia coli, is the best characterized protein of the molecular chaperone family. Here, we report on the in vitro formation of GroES amyloid-like fibrils and the mechanism of formation. When incubated for several weeks at neutral pH in the presence of the denaturant guanidine hydrochloride, GroES formed a typical amyloid fibril; unbranched, twisted, and extended filaments stainable by thioflavin T and Congo red. GroES fibril formation was accelerated by the addition of preformed fibril seeds, in accordance with a nucleation-extension mechanism. Interestingly, whereas the spontaneous formation of GroES fibrils was favored in the structural transition region of GroES dissociation/unfolding, the extension of fibrils from preformed fibril seeds was favored in the region corresponding to an expanded molecular state. We concluded that the two stages of GroES fibril formation prefer different molecular states of the same protein. The significance of this preference is discussed.     

Amyloid toxicity in skeletal myoblasts: Implications for inclusion-body myositis

Skeletal muscle disorder, inclusion-body myositis (IBM) has been known for accumulation of amyloid characteristic proteins in muscle. To understand the biophysical basis of IBM, the interaction of amyloid fibrils with skeletal myoblast cells (SMC) has been studied in vitro. Synthetic insulin fibrils and Aβ_25-35 fibrils were used for this investigation. From the saturation binding analysis, the calculated dissociation constant (K_d) for insulin fibril and Aβ_25-35 fibrils were 69.37 ± 11.17 nM and 115.60 ± 12.17 nM, respectively. The fibrillar insulin comparatively has higher affinity binding to SMC than Aβ fibrils. The competitive binding studies with native insulin showed that the amount of bound insulin fibril was significantly decreased due to displacement of native insulin. However, the presence of native insulin is not altered the binding of β-amyloid fibril. The cytotoxicity of insulin amyloid intermediates was measured. The pre-fibrillar intermediates of insulin showed significant toxicity (35%) as compared to matured fibrils. Myoblast treated with β-amyloid fibrils showed more oxidative damage than the insulin fibril. Cell differentiating action of amyloidic insulin was assayed by creatine kinase activity. The insulin fibril treated cells differentiated more slowly compared to native insulin. However, β-amyloid fibrils do not show cell differentiation property. These findings reinforce the hypothesis that accumulation of amyloid related proteins is significant for the pathological events that could lead to muscle degeneration and weakness in IBM.     

Amyloid-a state in many guises: survival of the fittest fibril fold

Under appropriate conditions, essentially all proteins are able to aggregate to form long, well-ordered and beta-sheet-rich arrays known as amyloid-like fibrils. These fibrils consist of varying numbers of intertwined protofibrils and can for any given protein exhibit a wealth of different forms at the ultrastructural level. Traditionally, this structural variability or polymorphism has been attributed to differences in the assembly of a common protofibril structure. However, recent work on glucagon, insulin, and the Abeta peptide suggests that this polymorphism can occur at the level of secondary structure. Simple variations in either solvent conditions such as temperature, protein concentration, and ionic strength or external mechanical influences such as agitation can lead to formation of fibrils with markedly different characteristics. In some cases, these characteristics can be passed on to new fibrils in a strain-specific manner, similar to what is known for prions. The preferred structure of fibrils formed can be explained in terms of selective pressure and survival of the fittest; the most populated types of fibrils we observe at the end of an experiment are those that had the fastest overall growth rate under the given conditions. Fibrillar polymorphism is probably a consequence of the lack of structural restraints on a nonfunctional conformational state.     

Identification of Glycosylated Subtypes of Interferon-α Produced by Human Leukocytes

We found that interferon-α produced by human leukocytes contained four subtypes that were glycosylated by N-linkages according to the results of lectin blot analysis. These glycosylated subtypes were type H or type ω and thei sugar moieties had no relation to their biological activities.     

Identification of β-aggregate sites in protein chains

The problem of amyloidoses is pressing and have recently attracted special attention throughout the world because of epidemics of prion diseases such as mad cow disease and human Creutzfeldt-Jacob disease. These diseases result from the conversion of a native protein or peptide into a highly stable pathological form. Molecules having a pathological conformation aggregate to form amyloid fibrils, capable of unlimited growth. It is important to study the molecular mechanisms of prion diseases and to identify the protein regions responsible for their development. The review considers theoretical and experimental works focusing on the formation of amyloid fibrils.     

Interpreting the aggregation kinetics of amyloid peptides

Amyloid fibrils are insoluble mainly beta-sheet aggregates of proteins or peptides. The multi-step process of amyloid aggregation is one of the major research topics in structural biology and biophysics because of its relevance in protein misfolding diseases like Alzheimer's, Parkinson's, Creutzfeld-Jacob's, and type II diabetes. Yet, the detailed mechanism of oligomer formation and the influence of protein stability on the aggregation kinetics are still matters of debate. Here a coarse-grained model of an amphipathic polypeptide, characterized by a free energy profile with distinct amyloid-competent (i.e. beta-prone) and amyloid-protected states, is used to investigate the kinetics of aggregation and the pathways of fibril formation. The simulation results suggest that by simply increasing the relative stability of the beta-prone state of the polypeptide, disordered aggregation changes into fibrillogenesis with the presence of oligomeric on-pathway intermediates, and finally without intermediates in the case of a very stable beta-prone state. The minimal-size aggregate able to form a fibril is generated by collisions of oligomers or monomers for polypeptides with unstable or stable beta-prone state, respectively. The simulation results provide a basis for understanding the wide range of amyloid-aggregation mechanisms observed in peptides and proteins. Moreover, they allow us to interpret at a molecular level the much faster kinetics of assembly of a recently discovered functional amyloid with respect to the very slow pathological aggregation.     

Crystallographic aspects of sub-elementary cellulose fibrils occurring in the wall of rose cells culturedin vitro

Summary Quantities of disencrusted sub-elementary cellulose fibrils from the cell wall of rose cells culturedin vitro were prepared. Following an X-ray and electron diffraction analysis, these fibrils gave a cellulose diffraction pattern which presented only two strong equatorial diffraction spacings at 0.409 and 0.572 nm indicating that the fibrils have a crystalline structure resembling that of cellulose IV_I. This observation is best explained in terms of a lateral disorganization of the cellulose chains within the fibrils. This disorganization cannot be eliminated and is connected with the small width of the fibrils which contain from 12 to 25 cellulose chains only. In these fibrils, most of the cellulose chains are superficial and not locked with neighboring chains in a tight hydrogen bond system as in thicker cellulose microfibrils.     

Stability of Aβ‐fibril fragments in the presence of fatty acids

We consider the effect of lauric acid on the stability of various fibril‐like assemblies of Aβ peptides. For this purpose, we have performed molecular dynamics simulations of these assemblies either in complex with lauric acid or without presence of the ligand. While we do not observe a stabilizing effect on Aβ₄₀‐fibrils, we find that addition of lauric acid strengthens the stability of fibrils built from the triple‐stranded S‐shaped Aβ₄₂‐peptides considered to be more toxic. Or results may help to understand how the specifics of the brain‐environment modulate amyloid formation and propagation.     

Collagen type I fibril packing in vivo and in vitro

Reviewed are works concerning the mechanisms of collagen (type I) fibril packing and the influence of macromolecular structure and physicochemical parameters of the medium on the process.     

Determination of amyloid core structure using chemical shifts

Amyloid fibrils are the pathological hallmark of a large variety of neurodegenerative disorders. The structural characterization of amyloid fibrils, however, is challenging due to their non‐crystalline, heterogeneous, and often dynamic nature. Thus, the structure of amyloid fibrils of many proteins is still unknown. We here show that the structure calculation program CS‐Rosetta can be used to obtain insight into the core structure of amyloid fibrils. Driven by experimental solid‐state NMR chemical shifts and taking into account the polymeric nature of fibrils CS‐Rosetta allows modeling of the core of amyloid fibrils. Application to the Y145X stop mutant of the human prion protein reveals a left‐handed β‐helix