Insights into microtubule nucleation from the crystal structure of human gamma-tubulin

Microtubules are hollow polymers of alphabeta-tubulin that show GTP-dependent assembly dynamics and comprise a critical part of the eukaryotic cytoskeleton. Initiation of new microtubules in vivo requires gamma-tubulin, organized as an oligomer within the 2.2-MDa gamma-tubulin ring complex (gamma-TuRC) of higher eukaryotes. Structural insight is lacking regarding gamma-tubulin, its oligomerization and how it promotes microtubule assembly. Here we report the 2.7-A crystal structure of human gamma-tubulin bound to GTP-gammaS (a non-hydrolysable GTP analogue). We observe a 'curved' conformation for gamma-tubulin-GTPgammaS, similar to that seen for GDP-bound, unpolymerized alphabeta-tubulin. Tubulins are thought to represent a distinct class of GTP-binding proteins, and conformational switching in gamma-tubulin might differ from the nucleotide-dependent switching of signalling GTPases. A crystal packing interaction replicates the lateral contacts between alpha- and beta-tubulins in the microtubule, and this association probably forms the basis for gamma-tubulin oligomerization within the gamma-TuRC. Laterally associated gamma-tubulins in the gamma-TuRC might promote microtubule nucleation by providing a template that enhances the intrinsically weak lateral interaction between alphabeta-tubulin heterodimers. Because they are dimeric, alphabeta-tubulins cannot form microtubule-like lateral associations in the curved conformation. The lateral array of gamma-tubulins we observe in the crystal reveals a unique functional property of a monomeric tubulin.     

扶手椅型石墨烯纳米带(AGNRs)电子结构的应力调控

当单轴拉伸应变沿扶手椅型石墨烯纳米带的扶手椅边沿时,利用静力学方法建立石墨烯纳米带的键角、键长与应力的解析关系;利用紧束缚方法对扶手椅边石墨烯纳米带的能带与能隙及应力的关系进行解析计算.研究结果表明:微小应变会导致纳米条带的能带宽度发生变化,并打开金属型扶手椅石墨烯纳米带能隙,费米能级附近的半导体型扶手椅石墨烯纳米带的能隙宽度也相应地发生改变;能隙随应变呈线性的周期变化,并且表现出明显的震荡现象;可达到的最大能隙随应力增大有所增大,随条带横向原子数m增大而减小.     

The 3.2-A crystal structure of the human IgG1 Fc fragment-Fc gammaRIII complex

The immune response depends on the binding of opsonized antigens to cellular Fc receptors and the subsequent initiation of various cellular effector functions of the immune system. Here we describe the crystal structures of a soluble Fc gamma receptor (sFc gammaRIII, CD16), an Fc fragment from human IgG1 (hFc1) and their complex. In the 1:1 complex the receptor binds to the two halves of the Fc fragment in contact with residues of the C gamma2 domains and the hinge region. Upon complex formation the angle between the two sFc gammaRIII domains increases significantly and the Fc fragment opens asymmetrically. The high degree of amino acid conservation between sFc gammaRIII and other Fc receptors, and similarly between hFc1 and related immunoglobulins, suggest similar structures and modes of association. Thus the described structure is a model for immune complex recognition and helps to explain the vastly differing affinities of other Fc gammaR-IgG complexes and the Fc epsilonRI alpha-IgE complex.     

An unusual feature revealed by the crystal structure at 2.2 A resolution of human transforming growth factor-beta 2.

Transforming growth factor type beta 2 (TGF-beta 2) is a member of an expanding family of growth factors that regulate proliferation and differentiation of many different cell types. TGF-beta 2 binds to various receptors, one of which was shown to be a serine/threonine kinase. TGF-beta 2 is involved in wound healing, bone formation and modulation of immune functions. We report here the crystal structure of TGF-beta 2 at 2.2 A resolution, which reveals a novel monomer fold and dimer association. The monomer consists of two antiparallel pairs of beta-strands forming a flat curved surface and a separate, long alpha-helix. The disulphide-rich core has one disulphide bone pointing through a ring formed by the sequence motifs Cys-Ala-Gly-Ala-Cys and Cys-Lys-Cys, which are themselves connected through the cysteines. Two monomers are connected through a single disulphide bridge and associate such that the helix of one subunit interacts with the concave beta-sheet surface of the other. Four exposed loop regions might determine receptor specificity. The structure provides a suitable model for the TGF-beta s and other members of the super-family and is the basis for the analysis of the TGF-beta 2 interactions with the receptor.     

Novel NADPH-binding domain revealed by the crystal structure of aldose reductase.

Aldose reductase is the first enzyme in the polyol pathway and catalyses the NADPH-dependent reduction of D-glucose to D-sorbitol. Under normal physiological conditions aldose reductase participates in osmoregulation, but under hyperglycaemic conditions it contributes to the onset and development of severe complications in diabetes. Here we present the crystal structure of pig lens aldose reductase refined to an R-factor of 0.232 at 2.5-A resolution. It exhibits a single domain folded in an eight-stranded parallel alpha/beta barrel, similar to that in triose phosphate isomerase and a score of other enzymes. Hence, aldose reductase does not possess the expected canonical dinucleotide-binding domain. Crystallographic analysis of the binding of 2'-monophospho-adenosine-5'-diphosphoribose, which competitively inhibits NADPH binding reveals that it binds into a cleft located at the C-terminal end of the strands of the alpha/beta barrel. This represents a new type of binding for nicotinamide adenine dinucleotide coenzymes.     

由过渡金属配合物修饰的硅钨多金属氧酸盐的合成与晶体结构

采用水热合成方法,得到了1种未见文献报道的过渡金属修饰的饱和Keggin 型硅钨多金属氧酸盐[Ni(2,2'-bipy)3]3{[Ni(2,2'-bipy)2(H2O)][SiW12O40]}2(OH)2 (2,2'-bipy=2,2'-联吡啶),并由X-射线单晶衍射确定了其晶体结构.化合物的基本单元由2个晶体学独立的阴离子{[Ni(2,2'-bipy)2 (H2O)][SiW12O40]} 2-、3个配离子[Ni(2,2'-bipy)3]2 及2个抗衡离子OH- 构成,在化合物中存在着复杂的氢键作用.在2个阴离子{[Ni(2,2'-bipy)2(H2O)][SiW12O40]}2-之间,通过分子间氢键形成二聚体,该二聚体进一步通过氢键形成链状超分子结构.     

The crystal structure of dynamin

Dynamin-related proteins (DRPs) are multi-domain GTPases that function via oligomerization and GTP-dependent conformational changes to play central roles in regulating membrane structure across phylogenetic kingdoms. How DRPs harness self-assembly and GTP-dependent conformational changes to remodel membranes is not understood. Here we present the crystal structure of an assembly-deficient mammalian endocytic DRP, dynamin 1, lacking the proline-rich domain, in its nucleotide-free state. The dynamin 1 monomer is an extended structure with the GTPase domain and bundle signalling element positioned on top of a long helical stalk with the pleckstrin homology domain flexibly attached on its opposing end. Dynamin 1 dimer and higher order dimer multimers form via interfaces located in the stalk. Analysis of these interfaces provides insight into DRP family member specificity and regulation and provides a framework for understanding the biogenesis of higher order DRP structures and the mechanism of DRP-mediated membrane scission events.     

二氯二(对溴苯胺)合锌(Ⅱ)配合物的合成和晶体结构

合成了二氯二(对溴苯胺)合锌(Ⅱ)配合物ZnCl2(p BrC6H4NH2)2,并测定了该配合物分子的晶体结构.该晶体属单斜晶系,空间群为C2 c,晶胞参数:a=3.1802(6)nm,b=0.46893(9)nm,c=1.1803(2)nm,β=110.83(3)°,V=1.6451(6)nm3,Z=4,Dc=1.939g·cm-3.对于1348(I≥2σ(I))个可观察点,最终偏差因子R=0.0565,wR=0.1538.两个对溴苯胺的2个胺基N原子和2个Cl-与Zn(Ⅱ)离子配位,形成畸变四面体Cl2N2Zn配位构型.     

Determination of crystal structure of omphacite

The chemical formula of omphacite was expressed with (MⅡ MⅠ ) (Si, AI)2O6. Cations that occupied the MⅡ site were large cations such as Ca or Na, and (Na/(Na+Ca)) ratio ranged from 0.2 to 0.8; the 6-coordinated MⅠ site accommodated cations such as Mg, Fe2+, Al, Fe3+ ,and(AI/(AI+Fe3+)) ratio was more than 0.5. Omphacite space groups reported were C2/ c, P2, P2/n, P2/c, cell parameters are α0 = 0.9600-0.9630 nm,b0 = 0.8750-0.8830 nm,c0 = 0.5230-0.5290 nm,β = 106°40′-107°10'. The sample was picked up from the eclogites in Zhucheng County, Shangdong Province. The intensity data were collected with the RIGAKU RASA Ⅱ -S four-circle single crystal diffractometer.The correct structure model was obtained by using the Patterson method and Fourier synthesis, SHELX-76 program, structure refinement with 905 independent diffraction points (| F0 |> 3σ |F0 |). After the structure parameter refinement, the R-factor reduced to 0.0515. The crystal structure analysis indicates that omphacite has a new space group-Pn space group.     

Covalent inhibition revealed by the crystal structure of the caspase-8/p35 complex

Apoptosis is a highly regulated process that is crucial for normal development and homeostasis of multicellular organisms. The p35 protein from baculoviruses effectively prevents apoptosis by its broad-spectrum caspase inhibition. Here we report the crystal structure of p35 in complex with human caspase-8 at 3.0 A resolution, and biochemical and mutagenesis studies based on the structural information. The structure reveals that the caspase is inhibited in the active site through a covalent thioester linkage to p35, which we confirmed by gel electrophoresis, hydroxylamine treatment and mass spectrometry experiments. The p35 protein undergoes dramatic conformational changes on cleavage by the caspase. The repositioning of the amino terminus of p35 into the active site of the caspase eliminates solvent accessibility of the catalytic dyad. This may be crucial for preventing hydrolysis of the thioester intermediate, which is supported by the abrogation of inhibitory activity through mutations at the N terminus of p35. The p35 protein also makes conserved contacts with the caspase outside the active-site region, providing the molecular basis for the broad-spectrum inhibitory activity of this protein. We demonstrate a new molecular mechanism of caspase inhibition, as well as protease inhibition in general.     

碱催化Aldol缩合反应制备丹皮酚衍生物及其晶体结构

探讨用碱催化通过Aldol缩合反应来制备丹皮酚的衍生物。常温下用碱催化使丹皮酚和4-硝基苯甲醛发生Aldol缩合反应,生成了一种新型的丹皮酚衍生物β-羟基-1-(2'-羟基-4'-甲氧基苯基)-β-(4-硝基苯基)-1-丙酮,产率高达77.34%,用紫外光谱、红外光谱、质谱并结合核磁共振的氢谱、碳谱以及135°DEPT谱综合表征其结构。用X-射线衍射技术分析该丹皮酚衍生物的单晶结构并确定其分子的构型和构象,β-羟基-1-(2'-羟基-4'-甲氧基苯基)-β-(4-硝基苯基)-1-丙酮属于单斜晶系中的p21/c空间群,晶胞参数a=0.874 9(15)nm、b=1.137 8(2)nm、c=1.554 0(3)nm、α=90.0°、β=106.5(8)°、γ=90°,晶胞体积为1.483 5(5)nm~3,晶胞个数为4个,密度为1.416 mg/cm~3。用碱催化可使丹皮酚和芳香醛通过Aldol缩合反应来制备丹皮酚衍生物。     

光子晶体加速结构的初步研究

用有限差分法计算了由金属棒按三角形晶格分布的二维光子晶体的带隙图，计算结果表明：当金属棒半径口和棒间距b比值小于0．2时，二雏光子晶体只有一务带隙，即若引入缺陷，可约束主模、抑制高次模．采用Microwave Studio计算了该种光子晶体微波加速结构的场型分布，结果显示当a／b〈0．2，类TM01模在缺陷中传输，类TM11模（横向模）能传出光子晶体．另外计算了结构尺寸公差对行波单元谐振频率的影响，还模拟计算了带有测试探针的由3个PBG单元构成的谐振腔的S参数．     

掺氟钨酸铅晶体的电子结构研究

用密度泛函的方法计算了掺氟钨酸铅晶体(F^-：PbWO4)的电子结构．结果表明，杂质F^-离子的掺入使得部分O的2p态和W的5d态分裂并进入到禁带中，使得禁带宽度变窄．F的2p态距离价带顶6．0eV左右，因而不会影响晶体的蓝发光．F^-离子替位氧离子O^2-可以部分地补偿由于铅空位VPb所造成的局域电荷失衡，阻止铅空位VPb抓住空穴形成复合色心．因此，可以减弱420nm吸收带，有效地增加光产额．     

新型三环己基锡羧酸酯的合成和晶体结构

以苯做溶剂,以2,5-二羧基-1,4-苯二甲酸二乙酯为配体,与三环己基氢氧化锡进行脱水反应,合成了新型三环己基锡羧酸酯配合物1.采用元素分析、1H NMR、红外光谱及X射线衍射等手段对其进行了结构表征,结果表明:配合物1为三方晶系,空间群为R3,a=b=3.039 4(4) nm,c=1.5637(2) nm,α=β=90°,γ=120°,V=12.510(3) nm3,z=9,D(,)=1.248 g/cm3,μ=9.43 nm-1,F(000)=4 878,R1=0.045 2,ωR2=0.090 7.配合物1是Sn原子化学环境相同的对称结构,Sn原子与3个环己基碳原子和1个羧基氧原子成键,中心Sn原子为畸变四面体构型.分子间的O→ Sn(0.3172 nm)配位作用,形成三维网状堆积结构.     

Y-shaped beam splitter by graded structure design in a photonic crystal

We propose a method to bend a self-collimated beam in a photonic crystal. The beam bending relies on the gradual variation of the constitutive parameters of the photonic crystal. A new Y-shaped beam splitter is designed with a composite structure constructed using two graded photonic crystals. We demonstrate that the incident beam is divided into two output beams by the designed splitter. The power ratio of the two beams can be adjusted easily by changing the location of the input beam.     

X射线衍射技术对环氧黄体酮单晶结构的解析

通过核磁共振谱、红外光谱、紫外光谱、质谱、薄层色谱以及元素分析等光谱学分析技术对环氧黄体酮的结构进行综合表征,并用X射线单晶衍射技术对环氧黄体酮的晶体结构进行解析,确定环氧黄体酮分子的构型和构象。环氧黄体酮晶体属于orthorhombic晶系,P212121空间群,其晶胞参数a=0.741 345(14)nm,b=1.384 5(3)nm,c=1.727 6(3)nm,α=β=γ=90.00°,晶胞体积V=1.773 2(6)nm3,Dc=1.230 mg/m3,每个晶胞中含有4个分子Z=4,F(000)=712。     

激光作用生成的网孔硅结构

作者结合量子受限效应,提出纳硅晶与氧化硅界面态发光模型来解释激光作用生成的纳米网孔壁结构的强荧光效应。将功率为50W、波长为1064nm的YAG激光束(束斑直径0.05mm)照射在硅样品表面打出小孔,在孔内的侧壁上,有很特殊的网孔形结构,其中的网孔壁厚为纳米尺度,这里有很强的受激荧光发光效应,发光峰中心约在700nm处。我们将激光与硅样品的作用隔离于无氧化的环境里,分别比较了将硅样品浸入酒精、氢氟酸和水中的激光加工结果,其发光情况证实了该发光模型的真实性。优化激光加工的条件,我们获得了较强发光的样品。     

工程结构裂纹监测技术

针对工程结构裂纹的产生和扩展原因,介绍了不同材料的裂纹监测技术,指出了基于传统方法的裂纹监测技术的缺陷和不足。在此基础上,着重分析了基于电子散斑干涉技术的结构裂纹监测技术的原理和应用。该技术用CCD相机将被测物体上的图像记录下来,并传输到计算机图像分析系统中进行存储和分析,经过图像处理和模式识别可以清楚地得到裂纹的图像,从而获得裂纹的各个参数;该技术可以实现对脆性材料和准脆性材料微小裂纹及裂纹尖端附近应力的监测。