Structure of C3b in complex with CRIg gives insights into regulation of complement activation

The complement system is a key part of the innate immune system, and is required for clearance of pathogens from the bloodstream. After exposure to pathogens, the third component of the complement system, C3, is cleaved to C3b which, after recruitment of factor B, initiates formation of the alternative pathway convertases. CRIg, a complement receptor expressed on macrophages, binds to C3b and iC3b mediating phagocytosis of the particles, but it is unknown how CRIg selectively recognizes proteolytic C3-fragments and whether binding of CRIg to C3b inhibits convertase activation. Here we present the crystal structure of C3b in complex with CRIg and, using CRIg mutants, provide evidence that CRIg acts as an inhibitor of the alternative pathway of complement. The structure shows that activation of C3 induces major structural rearrangements, including a dramatic movement (>80 A) of the thioester-bond-containing domain through which C3b attaches to pathogen surfaces. We show that CRIg is not only a phagocytic receptor, but also a potent inhibitor of the alternative pathway convertases. The structure provides insights into the complex macromolecular structural rearrangements that occur during complement activation and inhibition. Moreover, our structure-function studies relating the structural basis of complement activation and the means by which CRIg inhibits the convertases provide important clues to the development of therapeutics that target complement.     

Structure of C3b reveals conformational changes that underlie complement activity

Resistance to infection and clearance of cell debris in mammals depend on the activation of the complement system, which is an important component of innate and adaptive immunity. Central to the complement system is the activated form of C3, called C3b, which attaches covalently to target surfaces to amplify complement response, label cells for phagocytosis and stimulate the adaptive immune response. C3b consists of 1,560 amino-acid residues and has 12 domains. It binds various proteins and receptors to effect its functions. However, it is not known how C3 changes its conformation into C3b and thereby exposes its many binding sites. Here we present the crystal structure at 4-A resolution of the activated complement protein C3b and describe the conformational rearrangements of the 12 domains that take place upon proteolytic activation. In the activated form the thioester is fully exposed for covalent attachment to target surfaces and is more than 85 A away from the buried site in native C3 (ref. 5). Marked domain rearrangements in the alpha-chain present an altered molecular surface, exposing hidden and cryptic sites that are consistent with known putative binding sites of factor B and several complement regulators. The structural data indicate that the large conformational changes in the proteolytic activation and regulation of C3 take place mainly in the first conversion step, from C3 to C3b. These insights are important for the development of strategies to treat immune disorders that involve complement-mediated inflammation.     

Molecular genetics: DNA analysis of a putative dog clone

In August 2005, Lee et al. reported the first cloning of a domestic dog from adult somatic cells. This putative dog clone was the result of somatic-cell nuclear transfer from a fibroblast cell of a three-year-old male Afghan hound into a donor oocyte provided by a dog of mixed breed. In light of recent concerns regarding the creation of cloned human cell lines from the same institution, we have undertaken an independent test to determine the validity of the claims made by Lee et al..     

Arctic tropospheric warming amplification?

Relative rates of temperature change between the troposphere and surface, and the mechanisms that produce these changes, have long been a contentious issue. Graversen et al., predicated upon the ERA-40 reanalysis, report polar tropospheric amplification of surface warming and attempt to explain this finding dynamically. Here we show (1) that data from satellites and weather balloons indicate that the ERA-40 trends are increasingly unrealistic polewards of 62 degrees N; (2) that the two other reanalyses considered exhibit very different polar trends; and (3) that the vertical profile of polar trends in ERA-40 is unrealistic, particularly above the troposphere. These quasi-independent strands of evidence imply that the pattern of warming in the Arctic troposphere is highly unlikely to be as given in ERA-40 and as reported by Graversen et al..     

Quantum information: source of triggered entangled photon pairs?

The realization of an entangled photon source will be of great importance in quantum information--for example, for quantum key distribution and quantum computation--and Stevenson et al. have described such a source. However, we show here that first, their source is not entangled; second, they use inappropriate entanglement indicators that rely on assumptions invalidated by their data; and third, their source has insignificant entanglement even after simulating subtraction of the significant quantity of background noise. We therefore find that the standard of proof required for a semiconductor source of triggered entangled photon pairs has not been met by Stevenson et al..     

Cloning, sequencing and expression of a swine IgG H chain gene inE. coli

A DNA fragment about 1.5 kb has been isolated from spleen of adult Chinese swine by RT-PCR. The DNA fragment encodes immunoglobulin IgG H chain gene. Sequencing analysis showed that the DNA fragment is 1 425 bp long, complete CDS. The C region of the gene has been classified as Subclass Ig γ3, and is the same as reported by Sun et al., but V region of the present gene is 42 bp less by comparison. The gene has been ligated into expression vector pET-3b (NSEB)( - ). A protein about 52 ku has been expressed in E. coli with an expression level of about 21 % .     

The structure of complement C3b provides insights into complement activation and regulation

The human complement system is an important component of innate immunity. Complement-derived products mediate functions contributing to pathogen killing and elimination. However, inappropriate activation of the system contributes to the pathogenesis of immunological and inflammatory diseases. Complement component 3 (C3) occupies a central position because of the manifold biological activities of its activation fragments, including the major fragment, C3b, which anchors the assembly of convertases effecting C3 and C5 activation. C3 is converted to C3b by proteolysis of its anaphylatoxin domain, by either of two C3 convertases. This activates a stable thioester bond, leading to the covalent attachment of C3b to cell-surface or protein-surface hydroxyl groups through transesterification. The cleavage and activation of C3 exposes binding sites for factors B, H and I, properdin, decay accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46), complement receptor 1 (CR1, CD35) and viral molecules such as vaccinia virus complement-control protein. C3b associates with these molecules in different configurations and forms complexes mediating the activation, amplification and regulation of the complement response. Structures of C3 and C3c, a fragment derived from the proteolysis of C3b, have revealed a domain configuration, including six macroglobulin domains (MG1-MG6; nomenclature follows ref. 5) arranged in a ring, termed the beta-ring. However, because neither C3 nor C3c is active in complement activation and regulation, questions about function can be answered only through direct observations on C3b. Here we present a structure of C3b that reveals a marked loss of secondary structure in the CUB (for 'complement C1r/C1s, Uegf, Bmp1') domain, which together with the resulting translocation of the thioester domain provides a molecular basis for conformational changes accompanying the conversion of C3 to C3b. The total conformational changes make many proposed ligand-binding sites more accessible and create a cavity that shields target peptide bonds from access by factor I. A covalently bound N-acetyl-l-threonine residue demonstrates the geometry of C3b attachment to surface hydroxyl groups.     

A molecular basis for the two locus model of human complement component C4

The major histocompatibility complex(MHC)-linked fourth component of complement (C4) shows a high degree of polymorphism in several animal species. In man C4 polymorphism was detected by distinct charge differences of the variants. O'Neill et al. showed that this C4 polymorphism was controlled by two closely linked genetic loci, F (C4A) and S (C4B) and these results were extended by Awdeh et al. with an improved typing method. Biochemical analysis of human C4 has revealed that it consists of three polypeptide chains, alpha, beta and gamma. In all reports so far on the molecular analysis of human C4, no molecular weight differences between the A and B locus-encoded molecules have been noticed. Here we demonstrate that the C4A and C4B locus-encoded alpha-chains have a molecular weight (MW) of 96,000 and 94,000, respectively, presenting for the first time a molecular basis for the difference between all C4A and C4B variants tested. Even rare variants that are difficult to allocate to the A or B locus on the basis of charge differences could be identified as C4A or C4B variants in this way, thereby providing new insights into the relationships between the C4A and C4B loci.     

安徽黄精和琅琊黄精核型初步研究

本文对黄精属（Ｐｏｌｙｇｏｎａｔｕｍ Ｍｉｌｌ．）中安徽特有２种植物的核型进行了初步研究，并分别人近缘种的核型进行了比较。结果表明：安徽黄精（Ｐ．ａｎｈｕｉｅｎｓｅ）核型公式为２ｎ＝２４＝４ｍ＋６ｓｍ＋１２ｓｔ＝２Ｔ，属３Ｂ核型，染色体相对长度组成为２ｎ＝２４＝６Ｌ＋６Ｍ２＋６Ｍ１＋６Ｓ．琅琊黄精（Ｐ．ｌａｎｇｙａｅｎｓｅ）核型公式为２ｎ＝１８＝１０ｍ＋２ｓｍ＋６ｓｔ，属２Ｂ核型；染色体相对长度组     

Genetic defect in secretion of complement C5 in mice.

A genetic deficiency of the fifth (C5) component of complement1-3, a serum glycoprotein of molecular weight (MW) 220,000 (ref. 4), has been found in 39% of inbred strains of mice3. Sera of deficient mice lack detectable C5 activity and protein2,3. In addition deficient mice produce antibody to mouse C5 when injected with sera from C5 sufficient (normal) strains. Levy et al.5 showed that somatic cell hybrids between C5 deficient (B10.D2/old line) macrophages and either C5 sufficient (B10.D2/new line) mouse kidney or chicken erythroblasts secreted haemolytically active mouse C5 in vitro. Several possible molecular mechanisms to account for the findings were considered, but insufficient direct data were available to choose among them. We recently reported that mouse (CD.1 strain) peritoneal cells in culture synthesise and secrete a single chain precursor, pro-C5 (MW approximately 210,000), of the two-chain (alpha chain, 125,000 and beta chain 83,000 MW) C5 protein6. Radiolabelled precursor C5 was contained within the cells and was secreted into the tissue culture media. Using similar methods, we now find that C5 deficiency in each of five different mouse strains (AKR, SWR, DBA/2J8 A/HeJ and B10.D2/old line) is due to a failure in secretion of C5 protein and not to a failure in biosynthesis of pro-C5.     

Sleep behaviour: activity and sleep in dolphins

According to Lyamin and co-authors, neonate bottlenose dolphins (Tursiops truncatus) almost never sleep, unlike all other mammals that have been studied. Although we agree that young dolphins never stop and float at the surface, we find that they spend a considerable amount of time asleep while swimming. Our findings therefore call into question the conclusions of Lyamin et al..     

Immunology: Insulin auto-antigenicity in type 1 diabetes

Spontaneous type 1 diabetes occurs when the autoimmune destruction of pancreatic beta-islet cells prevents production of the hormone insulin. This causes an inability to regulate glucose metabolism, which results in dangerously raised blood glucose concentrations. It is generally accepted that thymus-derived lymphocytes (T cells) are critically involved in the onset and progression of type 1 diabetes, but the antigens that initiate and drive this destructive process remain poorly characterized--although several candidates have been considered. Nakayama et al. and Kent et al. claim that insulin itself is the primary autoantigen that initiates spontaneous type 1 diabetes in mice and humans, respectively, a result that could have implications for more effective prevention and therapy. However, I believe that this proposed immunological role of insulin may be undermined by the atypical responses of T cells to the human insulin fragment that are described by Kent et al..     

Properdin, the terminal complement components, thrombospondin and the circumsporozoite protein of malaria parasites contain similar sequence motifs

Properdin is a plasma glycoprotein which stabilizes the C3bnBb enzyme complex of the alternative pathway of the complement system. Unlike the classical pathway, which is initiated by interaction of C1q with the Fc regions of IgG or IgM antibodies in immune complexes, the alternative pathway can be directly activated via binding of C3b to surfaces of foreign organisms. The stabilized C3bnBbP complex activates components C3 and C5 resulting in opsonization of foreign material (via C3b) and assembly of the membrane attack complex (via C5b) on target cells. Therefore properdin greatly enhances complement-mediated clearance and inactivation mechanisms in both natural and acquired resistance to infection. This paper shows that the primary amino acid sequence of properdin is composed mainly of six repeating motifs, each of approximately 60 amino acids, and that similar sequences are found in thrombospondin, the circumsporozoite protein of malaria parasites and regions of the membrane-attack components of complement. These similarities may provide insight into the mechanisms by which parasites avoid host defences mediated by complement.     

二维层状超分子配合物[ VO( acac)2(H2O)].(C9H11N3OS)的合成、晶体结构及性质

甲醇和水混合溶剂中,邻羟基苯乙酮缩氨基硫脲(L=C9H11N3OS)和乙酰丙酮氧钒VO(acac)2,在醋酸钠存在下反应,得到一种新颖的二维层状超分子配合物[ vO(acac)2(H2O)]·(C9H11 N3OS).通过红外光谱和X-射线单晶衍射对其进行结构表征.该晶体属三斜晶系,P1空间群,晶胞参数为:α=0.78...     

电子波导间一维到一维隧穿的理论研究

研究了耦和电子波导间的电子隧穿，结果表明隧穿电导随波导宽度振荡，与已发表的实验结果相符。文中详细分析了电子的输运性质，并对量子力学计算与半经典的观点作了比较；结果表明半经典的观点能对有关现象给出定性的物理解释。     

硼铝硅系透明玻璃陶瓷晶相生长的分形动力学

通过熔融法结合两步热处理制度制备了硼铝硅系透明玻璃陶瓷.基于R.Kopelman等人对分形结构中扩散控制反应速率的研究结果,探讨了硼铝硅系透明玻璃陶瓷中晶相生长的分形动力学.结果表明,用分形结构扩散控制反应动力学理论来分析硼铝硅系透明玻璃陶瓷的晶化过程是行之有效的,通过实验数据拟合得出分形子谱维数dS=1.269.     

缅甸C Y油田构造特征及其与油气成藏关系研究

关于缅甸C Y油田构造特征及其与油气成藏关系研究,国内外研究相对较少。本文以新地层统层划分对比结果为基础,充分利用已有井及新钻井、测井资料、取芯资料、二维地震资料等,通过井震结合分析,对缅甸C Y油田浅层至深层地层构造特征进行了研究,包括：断裂特征、构造样式分析、构造格局及构造带分布、圈闭类型及特征分析研究等,总结了构造与油气运移聚集成藏的关系,指出了未来勘探重点潜力方向。     

Plant genetics: RNA cache or genome trash?

According to classical mendelian genetics, individuals homozygous for an allele always breed true. Lolle et al. report a pattern of non-mendelian inheritance in the hothead (hth) mutant of Arabidopsis thaliana, in which a plant homozygous at a particular locus upon self-crossing produces progeny that are 10% heterozygous; they claim that this is the result of the emerging allele having been reintroduced into the chromosome from a cache of RNA inherited from a previous generation. Here I suggest that these results are equally compatible with a gene conversion that occurred through the use as a template of DNA fragments that were inherited from a previous generation and propagated in archival form in the meristem cells that generate the plant germ lines. This alternative model is compatible with several important observations by Lolle et al..     

晶体电场对离子自旋─轨道耦合参数的影响

晶体电场对三价稀土离子自旋─轨道耦合参数有影响，是人们长期怀疑但尚无人作过定量分析与计算的问题．本文从相对论Ｄｉｒａｃ方程式给出的电子自族─轨道耦合参数表达式出发，以稀土氯化物为例，首次详细计算了晶体电场对稀土离子（Ｃｅ３＋、Ｐｒ３＋、Ｎｄ３＋、Ｓｍ３＋、Ｅｕ３＋、Ｇｄ３＋、Ｄｙ３＋、Ｅｒ３＋、Ｙｂ３＋）４ｆ自旋─轨道耦合参数贡献的相对大小．计算结果表明：晶体电场对电子自旋─轨道耦合参数的贡献至多占稀土离子核库仑场贡献的万分之一，因此可以忽略不计．寻找电子自旋─轨道耦合参数实验值与理论值差别的途径，应该从离子的电子结构本身着手来研究．     

金属材料非比例循环塑性的本构描述

多晶金属在非比例循环过程中的强化与其内部组织结构的变化密切相关。根据循环过程中金属位错子结构的变化,将强化函数分解为乘积形式,各因子分别决定于非强化区尺度与非比例度,由此将各种不同的强化机制嵌入热力学相容的本构方程。对304与316不锈钢室温下二维非比例循环的本构响应进行了分析,并与Benallal等、Tanaka等、和Ohashi等的实验结果进行比较,符合得很好。