植物铁蛋白结构、性质及其在纳米材料制备中的应用

铁蛋白具有储存铁及调节体内铁平衡的功能,它广泛存在于大多数生物体中.和动物铁蛋白相比,关于植物铁蛋白的研究至今很少.目前已知,植物铁蛋白主要存在于淀粉体中,而动物铁蛋白则主要存在于细胞质中.植物铁蛋白和动物铁蛋白相比,其在结构上有两个明显的特征:1.植物铁蛋白N端含有EP肽段,而动物铁蛋白则不具有.EP位于铁蛋白蛋白质外壳表面,现今发现它是作为铁蛋白第二个亚铁氧化中心,参与铁结合、氧化及种子萌发与早期生长的铁释放过程;2.在植物铁蛋白中只含有H亚基,即H-1和H-2,二者保持80％的同源性,这两个亚基在铁氧化沉淀中起着很好的协同作用. 由于铁蛋白具有特殊的结构,铁蛋白不仅可以在蛋白质内部空腔装载铁核,而且人们更多地利用脱铁铁蛋白( ApoFt)的蛋白质外壳作为载体装载其它可供利用的金属离子来装备新型生物纳米运载体系,因此植物铁蛋白在材料方面的应用也是很重要的.这篇综述主要着眼于植物铁蛋白的结构、功能及其在纳米材料方面的应用.     

A new synthetic approach to the ferritin core uncovers the soluble iron(III) oxo-hydroxo aggregate [Fe11O6(OH)6(O2CPh)15]

Hydrolytic polymerization of iron(III) occurs in many reactions in vivo, for example, the formation of bacterial magnetite in magnetotactic organisms, biomineralization of iron and the synthesis of the metallic core of the iron-storage protein ferritin. The ferritin core contains aggregates of up to 4,500 oxygen-bridged, octahedrally coordinated, high-spin iron(III) centres and is attached to the protein shell through carboxylate groups of amino-acid side chains. The X-ray and electron-diffraction patterns of this core resemble those of the mineral ferrihydrite, a hydrated iron oxide formed in nature, inter alia, by iron-dependent bacteria. The preparation and structural characterization of such large poly-iron aggregates has been a challenge to inorganic chemists. We have recently shown that tri- and tetranuclear iron(III) oxo complexes of the type thought to be important in ferritin-core formation can be prepared by reacting mononuclear [FeCl4]- and binuclear [Fe2OCl6]2- components in aprotic solvents (ref. 9 and S.M.G., W. H. Armstrong and S.J.L., in preparation). Here we report the discovery of a remarkable new molecule, [Fe11O6(OH)6(O2CPh)15], obtained by hydrolysis of the [Fe2O]4+ unit in the presence of limited amounts of water and carboxylate salts. The synthesis and properties of this soluble iron(III) oxohydroxo aggregate should help to elucidate the mechanism of formation of poly-iron centres.     

铁蛋白研究现状

铁蛋白是广泛存在于生物体的铁贮藏蛋白,具有调节铁代谢平衡、抗氧化胁迫、消除部分重金属和有毒分子的毒害等功能.随着其结构和功能研究的深入,铁蛋白逐渐成为相关领域研究的热点之一.铁蛋白在基因研究、与疾病的关系、生物反应器、分离与纯化、含量测定方法、铁释放动力学、纳米材料和抗体制备等方面都有了很大的进展.     

Crystallographic studies of the dynamic properties of lysozyme.

The patterns of atomic displacements in the crystals of hen and human lysozyme derived from independent crystallographic refinement are broadly similar. Analysis of the pattern indicates a close correlation with molecular structure, strongly suggestive of intramolecular motion. The active site of lysozyme is located in a region of high displacement. It is concluded that protein mobility may play a significant part in biological activity and that X-ray crystallography can contribute to its analysis.     

Structure of a Na+/H+ antiporter and insights into mechanism of action and regulation by pH

The control by Na+/H+ antiporters of sodium/proton concentration and cell volume is crucial for the viability of all cells. Adaptation to high salinity and/or extreme pH in plants and bacteria or in human heart muscles requires the action of Na+/H+ antiporters. Their activity is tightly controlled by pH. Here we present the crystal structure of pH-downregulated NhaA, the main antiporter of Escherichia coli and many enterobacteria. A negatively charged ion funnel opens to the cytoplasm and ends in the middle of the membrane at the putative ion-binding site. There, a unique assembly of two pairs of short helices connected by crossed, extended chains creates a balanced electrostatic environment. We propose that the binding of charged substrates causes an electric imbalance, inducing movements, that permit a rapid alternating-access mechanism. This ion-exchange machinery is regulated by a conformational change elicited by a pH signal perceived at the entry to the cytoplasmic funnel.     

{(PhCH2)2Sn[2,6-(O2C)2C5H3N](CH3OH)}2 的合成及结构

合成了七配位二聚体{(PhCH2)2Sn[2，6-(O2C)2C5H3N](CH3OH)}2。通过元素分析、红外光谱和核磁共振氢谱对其结构进行了表征。用X-射线单晶衍射测定了该化合物的晶体结构。化合物中两个锡原子呈七配位畸变五角双锥构型。     

Structure of D-ribulose-l,5-bisphosphate carboxylase/oxygenase from Alcaligenes eutrophyus H16

RuBPcase, D-ribulose-1,5-bisphosphate carboxylase/oxygenase (EC4.1.1.39) is the key enzyme of the reductive pentose phosphate cycle. Because of its biological significance, many structural studies on a number of plant and bacterial RuBPCases have been undertaken, including the enzyme isolated from the autotrophic hydrogen-oxidizing bacterium Alcaligenes eutrophus H16 (refs 2-6). Although both the higher plant enzyme and the A. eutrophus enzyme consist of eight large and eight small subunits (L(8)S(8)), no model describing the quaternary structure is generally accepted. Here we present a model for the A. eutrophus RuBPCase derived from X-ray crystallography of three-dimensional (3D) crystals, and electron microscopy and image analysis of two-dimensional (2D) crystals of the enzyme. The X-ray electron density of RuBPCase in the presence of HCO(-)(3), Mg(2+), and the transition state analogue 2-carboxyarabinitol-1,5-bisphosphate (CABP) shows an L(8)S(8) molecule in which the L(4)S(4) half molecules have local 4-fold symmetry (C4). The local 4-fold axes of the two L(4)S(4) halves do not coincide but are shifted by 36 ? and are related by a crystallographic 2-fold axis perpendicular to and between the local 4-fold axes. Electron microscope data of the enzyme without CABP, which can be perfectly modelled using the X-ray densities, do not show this shift and the low-resolution point group of the molecules in the 2D crystals is D4. Both structures are presented.     

Expression of functional interleukin-2 receptors in human light chain/Tac transgenic mice

The growth of mature T lymphocytes is regulated by interaction between interleukin-2 (IL-2) and its receptor. Three distinct binding sites for IL-2, namely low- (Kd 10 nM), intermediate- (Kd 100 pM) and high- (Kd 10 pM) affinity sites, have been found on human and primate T lymphocytes. Chemical crosslinking of labelled IL-2 to human T cells shows that two polypeptide chains, p55 (L chain) and p75 (H chain), bind IL-2 with low and intermediate affinities respectively. The high-affinity binding was shown to arise from ternary complex formation of IL-2, L and H chains. Construction of mutants of the L-chain complementary DNA indicated that the L chain is not directly involved in growth signal transduction. Nevertheless, expression of the IL-2 receptor L chain is tightly regulated by antigen or mitogen stimulation. To investigate the L chain function, we have produced transgenic mice using human L-chain cDNA of the IL-2 receptor under the control of a constitutive promoter. Studies on the L-chain transgenic mice showed that functionally active IL-2 receptors with high affinity were expressed on unstimulated spleen and thymus cells. The results indicate that the H chain of the IL-2 receptor is constitutively expressed in T cells.     

Correlation between fragmented immunoglobulin genes and heavy chain deletion mutants.

It is generally accepted that the variable (V) and constant (C) regions of immunoglobulin (Ig) chains are under separate genetic control. The notion that the different domains and interdomain regions are also under the control of independent genetic units was initially based on the clearcut results obtained by studying the primary structure of deletion mutants and received definitive support from direct analysis of cloned heavy (H) and light (L) chain genes. Here we present additional studies carried out on two selected gamma 3 deletion mutants which indicate the genetic control of human H chains may be even more complex than previously believed.     

Unusual sequences in the murine immunoglobulin mu-delta heavy-chain region

The delta heavy (H) chain of mouse immunoglobulin D (IgD) is unusual both in its structure and in its differential expression relative to immunoglobulin M (IgM; reviewed in ref. 1). The region of DNA between IgM and IgD H-chain constant-region genes is probably implicated in this control. So far only fragments of the area have been sequenced. Now, however, we present the complete sequence as well as the sequence of the introns of the C delta gene. We have found several interesting features (Fig. 1), including an open reading frame (ORF) between Cmu and C delta which encodes 146 amino acids that might represent a previously unsuspected domain-like protein; three blocks of simple repetitive sequences; a 162-base pair (bp) unique-sequence inverted repeat; and a domain-like pseudogene in the large intron of C delta. We have not found, however, any sequence 5' of C delta resembling the switch (S) recombination sequences associated with class switching in other heavy chains. Moreover, we have determined the 3' deletion end point of an IgD-producing myeloma and find no sequences reminiscent of switch sites nearby.     

铁蛋白反应器储存有毒金属离子的初步研究

探讨铁蛋白反应器在模拟流动海水体系中储存有毒金属离子的能力及规律.在体外,脱铁核铁蛋白能重新构建新的铁核且核中多数铁组分经含有5% 氯化钠的海水处理后仍可稳定于蛋白壳中,只有少量对H 或OH- 较敏感的铁组分随反应体系的pH值增加或减少而被直接释放于介质中.此外,铁蛋白还能储存Co2 、Ni2 、Mn2 和Zn2 等有毒金属离子,并释放相对应的铁量,其储存离子量和释放Fe3 量的摩尔比为1:1,该储存量及能力与环境介质的pH值有关,与Na 、K 、Ca2 等非过渡金属离子无关.经改造后的铁蛋白反应器预计可用于监测流动水域的有毒金属离子.     

Targeted disruption of mu chain membrane exon causes loss of heavy-chain allelic exclusion.

Burnet's clonal selection theory suggests that each B lymphocyte is committed to a single antibody specificity. This is achieved by a programme of somatic rearrangements of the gene segments encoding antibody variable (V) regions, in the course of B-cell development. Evidence from immunoglobulin-transgenic mice and immunoglobulin-gene-transfected transformed pre-B cells suggest that the membrane form of the immunoglobulin heavy (H) chain of class mu (microns), expressed from a rearranged H-chain (IgH) locus, may signal allelic exclusion of the homologous IgH locus in the cell and initiation of light (L)-chain gene rearrangement in the Ig kappa loci. We report here that targeted disruption of the membrane exon of the mu chain indeed results in the loss of H-chain allelic exclusion. But, some kappa chain gene rearrangement is still observed in the absence of micron expression.     

低硅高铁烧结矿矿物组成及显微结构特征

采用X射线衍射、光学显微镜和扫描电镜对五种试样烧结矿进行了研究,提出了以冀东地区铁精粉为主要原料的低硅高铁烧结矿的矿物组成和显微结构特征。研究发现,其矿物组成主要有磁铁矿、赤铁矿、铁酸钙和少量硅酸二钙、玻璃质,其中磁铁矿多呈他形,结晶粒度细小,赤铁矿主要以自形晶和少量的他形晶存在,铁酸钙多以柱状和针状形态存在。显微结构主要为交织结构和交织熔蚀结构,其中交织结构的冶金性能好,交织熔蚀结构冶金性能较差。在低硅条件下,以冀东型铁精粉为主要烧结原料的烧结矿的适宜碱度为2.2。     

Luminol-H2O2化学发光体系检测铁蛋白

酸性介质中, 铁蛋白(Ferritin)催化luminol-H2O2反应并产生很强的化学发光(CL)信号.基于此, 建立了简便灵敏的化学发光检测铁蛋白的分析方法,其线性范围为0.5～10 μg/L, 检出限(3σ)为0.36 μg/L,为铁蛋白作为纳米粒子标记物并直接检测提供了一种新的途径.     

两个Caco-2细胞系模型铁生物有效性评价效果研究

研究Caco-2细胞吸收转运模型(模型Ⅰ)和吸收转化模型(模型Ⅱ)对铁生物有效性的评价效果.用不同浓度,pH的硫酸亚铁溶液及稻米分别处理两种模型的Caco-2细胞单层22 h后,测定两种模型细胞铁吸收差异.结果表明Caco-2细胞铁蛋白形成量随铁浓度增加而增加,且模型I高于模型Ⅱ,当铁浓度≥25μmol.L-1时,差异达显著水平(p0.05);细胞铁蛋白形成量和转运铁量均与pH呈负相关,两模型间达到显著相关(p0.05).模型Ⅰ和模型Ⅱ均可用于膳食铁生物有效性评价,高铁浓度时,模型Ⅰ效果优于模型Ⅱ.     

六元瓜环与氯化钾分子的晶体结构

利用X-射线衍射方法测定六元瓜环(Q[6])与氯化钾分子形成的超分子自组装结构。在该化合物结构中,具有平行四边形结构的双氯化钾分子为"胶囊盖",包结了一个1,4-二氧六环分子的六元瓜环为"胶囊体",通过瓜环端口的羰基氧原子与钾离子的配位作用形成一个分子胶囊结构以及形成一维超分子链,进一步形成超分子结构实体。     

开放骨架稀土羧酸配合物的合成与结构表征

采用H2O/DMF混合溶剂热技术,选择咪唑羧酸衍生物和草酸混合配体与稀土金属铽配位合成了具有开放骨架结构的稀土咪唑羧酸配合物:[Tb(HpyimdC)(C2O4)0.5(H2O)]·(H2O)3(配合物1).X-射线单晶衍射等测试结果表明配合物1结晶在单斜晶系,C2/c空间群(No.15);草酸与稀土铽螯合配位形成一维zigzag链,再通过异位吡啶基咪唑羧酸的配位作用连接形成配合物1的三维开放骨架结构,沿y,z轴具有穿插超大孔道,客体分子位于孔道中.     

Crystals of haemoglobin with the T quaternary structure bind oxygen noncooperatively with no Bohr effect

The relationship between the structure and function of haemoglobin has mainly been studied by comparing its X-ray crystal structures with its function in solutions. To make a direct comparison we have studied the functional properties of haemoglobin in single crystals, an approach that has been an important part of the investigation of several enzyme mechanisms. Here we report on the oxygen binding by single crystals of human haemoglobin grown in solutions of polyethylene glycol. Unlike haemoglobin crystals formed in concentrated salt solution, which crack and become disordered on oxygenation, crystals grown in polyethylene glycol remain intact. X-ray studies have shown that the T (deoxy) quaternary structure of haemoglobin in this crystal at pH 7.0 is maintained at atmospheric oxygen pressure, and that the salt-bridges are not broken. We find striking differences between oxygen binding by haemoglobin in this crystal and by haemoglobin in solution. Not only is oxygenation of the crystal noncooperative, but the oxygen affinity is independent of pH in the range 6.0-8.5, and is much lower than that of the T state in solution. The lack of cooperativity without a change in quaternary structure is predicted by the two-state allosteric model of Monod, Wyman and Changeux. The absence of a Bohr effect without breakage of salt-bridges is predicted by Perutz's stereochemical mechanism. In contrast to the X-ray result that oxygen binds only to the alpha haems, our measurements show that the alpha haems have only a slightly higher affinity than the beta haems.