Anti-inflammatory activity of human IgG4 antibodies by dynamic Fab arm exchange

Antibodies play a central role in immunity by forming an interface with the innate immune system and, typically, mediate proinflammatory activity. We describe a novel posttranslational modification that leads to anti-inflammatory activity of antibodies of immunoglobulin G, isotype 4 (IgG4). IgG4 antibodies are dynamic molecules that exchange Fab arms by swapping a heavy chain and attached light chain (half-molecule) with a heavy-light chain pair from another molecule, which results in bispecific antibodies. Mutagenesis studies revealed that the third constant domain is critical for this activity. The impact of IgG4 Fab arm exchange was confirmed in vivo in a rhesus monkey model with experimental autoimmune myasthenia gravis. IgG4 Fab arm exchange is suggested to be an important biological mechanism that provides the basis for the anti-inflammatory activity attributed to IgG4 antibodies.     

鱼类免疫球蛋白生物合成的遗传控制研究综述

真骨鱼重链IgM恒定区基因由CH1～CH44个外显子所编码,以IgM分泌型表达,其跨膜域由2个外显子所编码,它以淋巴细胞膜受体形式被利用,TM1外显子被直接剪接到CH3外显子,而不是在CH4外显子内,这种不寻常的剪接方式导致产生Cμ4区的膜IgM。真骨鱼IgD重链除包括分泌型或膜结合型的C末端外,这个重组分子还包括1个重组的可变区、μ链的第1个恒定区及7个恒定区。IgD(δ)重链基因恰好位于IgM(μ)基因下游,第1个恒定区μ外显子被剪切形成δ转录本。     

Tertiary structure of plant RuBisCO: domains and their contacts

The three-dimensional structure of ribulose-1,5-biphosphate carboxylase-oxygenase (RuBisCO), has been determined at 2.6 A resolution. This enzyme initiates photosynthesis by combining carbon dioxide with ribulose bisphosphate to form two molecules of 3-phosphoglycerate. In plants, RuBisCO is built from eight large (L) and eight small (S) polypeptide chains, or subunits. Both S chains and the NH2-terminal domain (N) of L are antiparallel beta, "open-face-sandwich" domains with four-stranded beta sheets and flanking alpha helices. The main domain (B) of L is an alpha/beta barrel containing most of the catalytic residues. The active site is in a pocket at the opening of the barrel that is partly covered by the N domain of a neighboring L chain. The domain contacts of the molecule and its conserved residues are discussed in terms of this structure.     

C-cadherin ectodomain structure and implications for cell adhesion mechanisms

Cadherins are transmembrane proteins that mediate adhesion between cells in the solid tissues of animals. Here we present the 3.1 angstrom resolution crystal structure of the whole, functional extracellular domain from C-cadherin, a representative "classical" cadherin. The structure suggests a molecular mechanism for adhesion between cells by classical cadherins, and it provides a new framework for understanding both cis (same cell) and trans (juxtaposed cell) cadherin interactions. The trans adhesive interface is a twofold symmetric interaction defined by a conserved tryptophan side chain at the membrane-distal end of a cadherin molecule from one cell, which inserts into a hydrophobic pocket at the membrane-distal end of a cadherin molecule from the opposing cell.     

Interaction of the IL-2 receptor with the src-family kinase p56lck: identification of novel intermolecular association

In the interleukin-2 (IL-2) system, intracellular signal transduction is triggered by the beta chain of the IL-2 receptor (IL-2R beta); however, the responsible signaling mechanism remains unidentified. Evidence for the formation of a stable complex of IL-2R beta and the lymphocyte-specific protein tyrosine kinase p56lck is presented. Specific association sites were identified in the tyrosine kinase catalytic domain of p56lck and in the cytoplasmic domain of IL-2R beta. As a result of interaction, IL-2R beta became phosphorylated in vitro by p56lck. Treatment of T lymphocytes with IL-2 promotes p56lck kinase activity. These data suggest the participation of p56lck as a critical signaling molecule downstream of IL-2R via a novel interaction.     

猪T细胞受体β链基因的克隆及生物信息学分析

以GenBank上登载的猪的T细胞受体β(pTCR-β)基因为参考序列,用RT-PCR法从猪的外周血淋巴细胞中克隆了TCR-β链基因,并进行生物信息学分析.结果表明:pTCR-β基因含有一个完整的开放阅读框架(ORF),大小为849bp,编码283个氨基酸,且含有一段27个氨基酸的信号肽序列,与参考序列相比,在核苷酸序列上的同源性为80.4%,在氨基酸序列上的同源性为70.3%;生物信息学结构预测发现2个结构域,一个为IG结构域,由第32-138位共107个氨基酸残基组成;另一个为IG-LIKE结构域,由第164-211位共48个氨基酸残基组成.     

Platelet membrane glycoprotein IIb/IIIa: member of a family of Arg-Gly-Asp--specific adhesion receptors

Adhesive interactions of the platelet surface with plasma proteins such as fibrinogen and fibronectin play an important role in thrombosis and hemostasis. The binding of both of these proteins to platelets is inhibited by synthetic peptides containing the sequence Arg-Gly-Asp, which corresponds to the cell adhesion site in fibronectin and is also present in the alpha chain of fibrinogen. An affinity matrix made of an insolubilized heptapeptide containing the Arg-Gly-Asp sequence selectively binds the platelet membrane glycoprotein IIb/IIIa from detergent extracts of platelets. When incorporated into liposome membranes, the isolated protein confers to the liposomes the ability to bind to surfaces coated with fibrinogen, fibronectin, and vitronectin but not to surfaces coated with thrombospondin or albumin. This platelet receptor is related to the previously identified fibronectin and vitronectin receptors in that it recognizes an Arg-Gly-Asp sequence but differs from the other receptors in its wider specificity toward various adhesive proteins. These results establish the existence of a family of adhesion receptors that recognize the sequence Arg-Gly-Asp.     

A G protein mutant that inhibits thrombin and purinergic receptor activation of phospholipase A2

The stimulation of phospholipase A2 by thrombin and type 2 (P2)-purinergic receptor agonists in Chinese hamster ovary cells is mediated by the G protein Gi. To delineate alpha chain regulatory regions responsible for control of phospholipase A2, chimeric cDNAs were constructed in which different lengths of the alpha subunit of Gs (alpha s) were replaced with the corresponding sequence of the Gi alpha subunit (alpha i2). When a carboxyl-terminal chimera alpha s-i(38), which has the last 38 amino acids of alpha s substituted with the last 36 residues of alpha i2, was expressed in Chinese hamster ovary cells, the receptor-stimulated phospholipase A2 activity was inhibited, although the chimera could still activate adenylyl cyclase. Thus, alpha s-i(38) is an active alpha s, but also a dominant negative alpha i molecule, indicating that the last 36 amino acids of alpha i2 are a critical domain for G protein regulation of phospholipase A2 activity.     

茶树中精氨酸脱羧酶基因的cDNA克隆及序列分析

通过SMARTRACE PCR技术获得了茶树中精氨酸脱羧酶(ADC)的cDNA全长序列,并登录GenBank(登录号为JQ653274)。ADC基因cDNA全长为2 988 bp,开放阅读框(ORF)全长为2 163 bp,共编码720个氨基酸,编码的蛋白质的分子量为77.430 kDa,理论等电点为5.373,其序列中不存在卷曲螺旋结构。ADC蛋白为亲水性非分泌不稳定蛋白,不跨膜运动,无信号肽序列存在,共有41个可能的磷酸化位点,存在于叶绿体基质中,是细胞质蛋白。精氨酸脱羧酶的基因cDNA全长序列的获得,对于进一步研究精氨酸在茶树氮代谢中的作用及茶氨酸代谢途径提供基础。     

Programmed cell death of T cells signaled by the T cell receptor and the alpha 3 domain of class I MHC

As well as being activated or rendered unresponsive, mature T lymphocytes can be deleted, depending on the signals received by the cell. Deletion by programmed cell death (apoptosis) is triggered if a T cell that has received a signal through its T cell receptor complex also receives a signal through the alpha 3 domain of its class I major histocompatibility complex (MHC) molecule. Such a signal can be delivered by a CD8 molecule, which recognizes the alpha 3 domain, or by an antibody to this domain. Precursors of both cytotoxic T lymphocytes (CTL's) and T helper cells are sensitive to this signal but become resistant at some point before completing differentiation into functioning CTL's or T helper cells. Because CTL's carry CD8, they can induce cell death in T cells that recognize them. This pathway may be important in both removal of autoreactive T cells and immunoregulation.     

花楸树热激蛋白SpHSP70-2基因的克隆及表达分析

探究花楸树响应高温胁迫的分子机制,为遗传改良和耐热品种的选育提供基础,依托花楸树叶片转录组测序数据,采用反转录PCR（RT-PCR）方法克隆得到HSP70家族中的1个基因,命名为SpHSP70-2,同时对该基因进行了生物信息学分析,利用荧光定量PCR（qRT-PCR）方法对其组织特异性和应答高温胁迫的表达模式进行了分析。结果表明,经克隆得到的SpHSP70-2基因与花楸树叶片转录组测序数据的基因序列一致,SpHSP70-2开放阅读框（ORF）长度为1 704 bp,编码567个氨基酸。SpHSP70-2蛋白具有HSP70特征结构域:核苷酸结合结构域（NBD）和底物结合结构域（SBD）;SpHSP70-2基因无内含子;SpHSP70-2二级结构中具有ɑ螺旋（32.63%）、延伸链（23.28%）、β转角（7.23%）和随机卷曲链（36.86%）;SpHSP70-2蛋白为疏水性蛋白,有11个跨膜螺旋,无信号肽;SpHSP70-2与同科的苹果、白梨的HSP70同源性最高,为90%以上;SpHSP70-2在花楸树的果实中表达量最大,在茎、根中表达量次之,在花中的表达量最小;在42℃高温胁迫处理下,SpHSP70-2表达量呈现先升高后下降趋势,在2 h时达到极值,随后表达量略缓慢下降,说明SpHSP70-2基因参与调控花楸树对高温胁迫的响应。研究结果为今后花楸树响应热胁迫的分子机制研究和引种驯化方面提供基础。     

Selective phagocytosis: a new concept in protein catabolism

The clearance of different metabolic products derived from two plasma proteins, prothrombin and fibrinogen, was studied with the aid of the isolated, perfused rat liver. Active thrombin and fibrin were rapidly cleared by the Kupffer cells. Inactive thrombin and a partially degraded fibrin molecule were also cleared but at much slower rates. This difference in clearance rates suggests the presence of a high degree of selectivity in the clearance of altered plasma proteins.     

Antibody-directed urokinase: a specific fibrinolytic agent

A specific fibrinolytic agent was synthesized by covalently coupling urokinase to a monoclonal antibody that was fibrin-specific and did not cross-react with fibrinogen. The antibody was raised against a synthetic peptide representing the seven amino-terminal residues of the beta chain of human fibrin. The urokinase-antifibrin conjugate retained the original binding specificity of the antibody and showed 100-fold increased fibrinolysis in vitro when compared to unmodified urokinase. The presence of human fibrinogen at plasma concentration did not influence these properties.     

Lutropin-choriogonadotropin receptor: an unusual member of the G protein-coupled receptor family

A complementary DNA (cDNA) for the rat luteal lutropin-choriogonadotropin receptor (LH-CG-R) was isolated with the use of a DNA probe generated in a polymerase chain reaction with oligonucleotide primers based on peptide sequences of purified receptor protein. As would be predicted from the cDNA sequence, the LH-CG-R consists of a 26-residue signal peptide, a 341-residue extracellular domain displaying an internal repeat structure characteristic of members of the leucine-rich glycoprotein (LRG) family, and a 333-residue region containing seven transmembrane segments. This membrane-spanning region displays sequence similarity with all members of the G protein-coupled receptor family. Hence, the LH-CG-R gene may have evolved by recombination of LRG and G protein-coupled receptor genes. Cells engineered to express LH-CG-R cDNA bind human choriogonadotropin with high affinity and show an increase in cyclic adenosine monophosphate when exposed to hormone. As revealed by RNA blot analysis and in situ hybridization, the 4.4-kilobase cognate messenger RNA is prominently localized in the rat ovary.     

ISSR分子标记及其在树木遗传育种研究中的应用

在比较ISSR和其它分子标记的原理和特点的基础上,综述了ISSR分子标记在树木遗传多样性研究、亲缘关系及系谱分析、优良种质和品种鉴定及遗传连锁图谱的构建等领域的研究进展,指出了目前ISSR分子标记在树木遗传改良和辅助育种等研究领域存在的问题,并提出今后的研究方向。     

Modulation of alpha-thrombin function by distinct interactions with platelet glycoprotein Ibalpha

Thrombin bound to platelets contributes to stop bleeding and, in pathological conditions, may cause vascular thrombosis. We have determined the structure of platelet glycoprotein Ibalpha (GpIbalpha) bound to thrombin at 2.3 angstrom resolution and defined two sites in GpIbalpha that bind to exosite II and exosite I of two distinct alpha-thrombin molecules, respectively. GpIbalpha occupancy may be sequential, as the site binding to alpha-thrombin exosite I appears to be cryptic in the unoccupied receptor but exposed when a first thrombin molecule is bound through exosite II. These interactions may modulate alpha-thrombin function by mediating GpIbalpha clustering and cleavage of protease-activated receptors, which promote platelet activation, while limiting fibrinogen clotting through blockade of exosite I.