Direct evidence that endogenous GM1 ganglioside can mediate thymocyte proliferation

The B subunit of cholera toxin, which is multivalent and binds exclusively to a specific ganglioside, GM1, was mitogenic for rat thymocytes. When exposed to the B subunit, the cells proliferated, as measured by 3H-labeled thymidine incorporation. Mitogenesis depended on the direct interaction of the B subunit with GM1 on the surface of the cells. This demonstrates that endogenous plasma membrane gangliosides can mediate proliferation in lymphocytes.     

Mutants of pertussis toxin suitable for vaccine development

Immunization with chemically detoxified pertussis toxin can prevent severe whooping cough with an efficacy similar to that of the cellular pertussis vaccine, which normally gives unwanted side effects. To avoid the reversion to toxicity and the loss of immunogenicity that may follow chemical treatment of pertussis toxin, inactive toxins were constructed by genetic manipulation. A number of genetically engineered alleles of the pertussis toxin genes, constructed by replacing either one or two key amino acids within the enzymatically active S1 subunit, were introduced into the chromosome of strains of Bordetella pertussis, B. parapertussis, and B. bronchiseptica. These strains produce mutant pertussis toxin molecules that are nontoxic and immunogenic and that protect mice from the intracerebral challenge with virulent Bordetella pertussis. Such molecules are ideal for the development of new and safer vaccines against whooping cough.     

Structure of the rotor of the V-Type Na+-ATPase from Enterococcus hirae

The membrane rotor ring from the vacuolar-type (V-type) sodium ion-pumping adenosine triphosphatase (Na+-ATPase) from Enterococcus hirae consists of 10 NtpK subunits, which are homologs of the 16-kilodalton and 8-kilodalton proteolipids found in other V-ATPases and in F1Fo- or F-ATPases, respectively. Each NtpK subunit has four transmembrane alpha helices, with a sodium ion bound between helices 2 and 4 at a site buried deeply in the membrane that includes the essential residue glutamate-139. This site is probably connected to the membrane surface by two half-channels in subunit NtpI, against which the ring rotates. Symmetry mismatch between the rotor and catalytic domains appears to be an intrinsic feature of both V- and F-ATPases.     

Immune response to cholera toxin epitope inserted in Salmonella flagellin

Bacterial flagella are potent immunogens and aromatic-dependent (aro) Salmonella as live vaccines evoke humoral and cellular immune responses. Such strains expressing epitopes of protective antigens as inserts in flagellin would provide a novel way to vaccinate against diseases caused by unrelated pathogens. A synthetic oligonucleotide specifying an epitope of cholera toxin subunit B was inserted in a Salmonella flagellin gene. The chimeric flagellin functioned normally and the epitope was expressed at the flagellar surface. Parenteral administration to mice of an aro A flagellin-negative strain of S. dublin expressing the chimeric flagellin gene evoked antibody to cholera toxin.     

Structure of the rotor ring of F-Type Na+-ATPase from Ilyobacter tartaricus

In the crystal structure of the membrane-embedded rotor ring of the sodium ion-translocating adenosine 5'-triphosphate (ATP) synthase of Ilyobacter tartaricus at 2.4 angstrom resolution, 11 c subunits are assembled into an hourglass-shaped cylinder with 11-fold symmetry. Sodium ions are bound in a locked conformation close to the outer surface of the cylinder near the middle of the membrane. The structure supports an ion-translocation mechanism in the intact ATP synthase in which the binding site converts from the locked conformation into one that opens toward subunit a as the rotor ring moves through the subunit a/c interface.     

Diphtheria toxin subunit active in vitro

Exposure of diphtheria toxin to dithiothreitol (and similar thiols) resulted in a subunit which was active in catalyzing the adenosine diphosphateribosylation of mammalian aminoacyl-transferase II in the presence of nicotinamide adenine dinucleotide. At the same time there was a marked increase in total ADP-ribosylation activity. A molecule which was apparently identical to the derived subunit in size and activity was detected in partially purified preparations of toxin.     

大豆24 kDa油体蛋白基因在大肠杆菌中的表达

 分别构建了含全长大豆24 kDa油体蛋白基因、与大肠杆菌热敏毒素B亚基和定居因子CS6 B亚基基因以串联方式融合的全长大豆24 kDa油体蛋白基因、缺失N端74个氨基酸编码序列的油体蛋白基因及缺失C端152个氨基酸编码序列油体蛋白基因等4个大肠杆菌表达载体。除N端缺失的油体蛋白基因外,其它3个载体的IPTG诱导表达产物对E.coli生长表现出明显的抑制作用,菌液浓度与对照菌株相比,至少降低了3倍;而N端缺失了222个编码核苷酸的油体蛋白基因则对宿主细菌细胞的生长繁殖不再表现有任何毒性。进一步通过SDS-PAGE和Western印迹反应检测各表达载体的IPTG诱导表达产物时发现,仅有N端缺失的24 kDa油体蛋白基因片段在宿主细胞BL21(DE3)和Rosseta(DE3)中有重组油体蛋白积累。     

Pertussis toxin inhibition of B cell and macrophage responses to bacterial lipopolysaccharide

Lipopolysaccharide, a component of the outer membrane of Gram-negative bacteria, activates B lymphocytes and macrophages. Pertussis toxin, which inactivates several members of the G protein family of signaling components, including Gi and transducin, was found to inhibit the lipopolysaccharide-induced responses of the WEHI-231 B lymphoma cell line and the P388D1 macrophage cell line. These results, combined with the demonstration that lipopolysaccharide inhibits adenylate cyclase activity in P388D1 cells, strongly argues that lipopolysaccharide activation of cells is mediated by a Gi-like receptor-effector coupling protein.     

菌核菌粗毒素对向日葵种子及幼苗的毒害作用

利用向日葵菌核菌粗毒素和病菌培养滤液处理向日葵的种子和幼苗,研究粗毒素对种子萌发、胚根生长的影响,对幼苗的致萎作用、对幼苗离体叶片的致病作用以及对叶片细胞膜透性的影响。结果表明:菌核菌粗毒素对向日葵种子萌发、胚根伸长和幼苗生长都有毒害或抑制作用,对离体叶片也具有强烈的致病作用,且粗毒素和培养滤液引起的症状基本相同。同时,草酸毒素可作用于寄主细胞膜,引起细胞膜透性的增加,造成膜功能的紊乱。     

Structural basis for the activation of cholera toxin by human ARF6-GTP

The Vibrio cholerae bacterium causes devastating diarrhea when it infects the human intestine. The key event is adenosine diphosphate (ADP)-ribosylation of the human signaling protein GSalpha, catalyzed by the cholera toxin A1 subunit (CTA1). This reaction is allosterically activated by human ADP-ribosylation factors (ARFs), a family of essential and ubiquitous G proteins. Crystal structures of a CTA1:ARF6-GTP (guanosine triphosphate) complex reveal that binding of the human activator elicits dramatic changes in CTA1 loop regions that allow nicotinamide adenine dinucleotide (NAD+) to bind to the active site. The extensive toxin:ARF-GTP interface surface mimics ARF-GTP recognition of normal cellular protein partners, which suggests that the toxin has evolved to exploit promiscuous binding properties of ARFs.     

2013年四川省饲料原料中霉菌毒素污染情况调查

为了解2013年四川省饲料原料受霉菌毒素的污染情况,采集四川省饲料原料120个,采用酶联试剂盒和液质联用仪两种方法,测定其中黄曲霉毒素B1、玉米赤霉烯酮、呕吐毒素、赭曲霉毒素A和T-2毒素的含量。结果表明,四川省饲料原料中霉菌毒素超标率均低于全国平均水平,玉米赤霉烯酮和呕吐毒素污染程度相对较重,黄曲霉毒素B1、赭曲霉毒素A和T-2毒素超标率为0。     

Reconstitution of diphtheria toxin from two nontoxic cross-reacting mutant proteins

The isolation of a new type of mutant Corynephage beta, which carries a missense mutation in the structural gene for diphtheria toxin synthesis is described. The lysogenic C7(8)(beta(197))(tox-crm+) strain of Corynebacterium diphtheriae produces a nontoxic, extracellular protein of molecular weight 62,000. This protein is immunologically indistinguishable from toxin itself but inhibits the action of toxin on HeLa cells, probably by competing for attachment sites on the cell membrane. In contrast to fragment A derived from diphtheria toxin, fragment A(197) is unable to catalyze the inactivation of eucaryotic polypeptidyl-transfer RNA-transferase II. When mixtures of the two nontoxic mutant proteins, enzymically active crm(45) protein and enzymically inactive crm(197) protein, are subjected to mild treatment with trypsin in the presence of a thiol and then allowed to reoxidize after dialysis to remove excess thiol, "diphtheria toxin" is reconstituted in high yield.     

Sequence of the alpha subunit of photoreceptor G protein: homologies between transducin, ras, and elongation factors

A bovine retinal complementary DNA clone encoding the alpha subunit of transducin (T alpha) was isolated with the use of synthetic oligodeoxynucleotides as probes, and the complete nucleotide sequence of the insert was determined. THe predicted protein sequence of 354 amino acids includes the known sequences of four tryptic peptides and sequences adjacent to the residues that undergo adenosine diphosphate ribosylation by cholera toxin and pertussis toxin. On the basis of homologies to other proteins, such as the elongation factors of protein synthesis and the ras oncogene proteins, regions are identified that are predicted to be acylated and involved in guanine nucleotide binding and hydrolysis. Amino acid sequence similarity between T alpha and ras is confined to these regions of the molecules.     

玉米大斑病菌HT-毒素对玉米细胞膜透性的影响

玉米大斑病菌ＨＴ－毒素粗毒素、通过硅胶Ｇ柱层析获得的组分Ｉ、５－羟甲基－２－呋喃甲醛对玉米细胞膜都具有明显的损伤作用,且与毒素浓度和处理时间呈正相关。试验发现,来自２号小种的ＨＴ－粗毒素因含有组分ＩＶ、对ＯＨ４３Ｈｔ１玉米细胞膜的损伤要比组分Ｉ和５－羟甲基－２－呋喃甲醛强的多。ＨＴ－毒素中外源加入强氧化剂Ｈ２Ｏ２后,可提高毒素对细胞膜的破坏作用,尤其是５－羟甲基－２－呋喃甲醛加入Ｈ２Ｏ２后对叶片细胞膜的破坏作用更加明显。结论初步判断,ＨＴ－毒素的原初作用位点可能在感病玉米的细胞膜上。     

青稞高分子量麦谷蛋白亚基SDS PAGE分析

 对87份青稞和13份野生大麦进行SDS PAGE分析,结果发现,供试材料的HMW GS条带单一,大多只有1条带,个别材料有2条带,而且条带的位置也变化不大,仅有3种条带位置,且基本介于小麦HMW GS的7亚基至12亚基位置之间。因此,根据条带迁移位置的不同对参试材料的3种条带命名为A,B,C,分别对应着A,B,C亚基。87份青稞材料共出现了A,B,C,AC等4种带型,分别对应着56,1,27,3号青稞材料,各带型分别占64.4%,1.1%,31.0%,3.4%;其中A,B,C为单带带型,AC为双带带型;出现AC带型的原因是材料中同时存在A带型和C带型的种子。青稞和野生大麦高分子量麦谷蛋白亚基类型较单一,变异不丰富,多态性较低。本试验对青稞高分子量麦谷蛋白亚基多态性的研究可为其面粉加工利用和品质改良提供科学依据     

小麦品种麦谷蛋白亚基的遗传变异分析

分析了９６个小麦品种高、低分子量麦谷蛋白亚基组成的及其分布规律,结果表明：强面筋品种与普通品种在高分子量及低分子量麦谷蛋白亚基组成上存在明显差异。强面筋品种含Ｇｌｕ－Ａｌａ（１亚基）、Ｇｌｕ－Ａ１ｂ（２＾＊亚基）、Ｇｌｕ－Ｂ１ｂ（７＋８亚基）、Ｇｌｕ－Ｂｌｉ（１７＋１８亚基）、Ｇｌｕ－Ｄｌｄ（５＋１０亚基）、Ｇｌｕ－Ａ３ｂ和Ｇｌｕ－Ｄ３ｃ的频率较高,而普通品种则含Ｇｌｕ－Ａｌｃ（Ｎ）、Ｇｌｕ－Ｂｌ     

Biosynthesis of the Torpedo californica acetylcholine receptor alpha subunit in yeast

Yeast cells were transformed with a plasmid containing complementary DNA encoding the alpha subunit of the Torpedo californica acetylcholine receptor. These cells synthesized a protein that had the expected molecular weight, antigenic specificity, and ligand-binding properties of the alpha subunit. The subunit was inserted into the yeast plasma membrane, demonstrating that yeast has the apparatus to express a membrane-bound receptor protein and to insert such a foreign protein into its plasma membrane. The alpha subunit constituted approximately 1 percent of the total yeast membrane. The alpha subunit constituted approximately 1 percent of the total yeast membrane proteins, and its density was about the same in the plasma membrane of yeast and in the receptor-rich electric organ of Electrophorus electricus. In view of the available technology for obtaining large quantities of yeast proteins, it may now be possible to obtain amplified amounts of interesting membrane-bound proteins for physical and biochemical studies.     

芸薹根肿菌毒素对油菜幼苗生理 性状及生长的影响

为探索芸薹根肿菌的致病作用、采用水培法研究根肿菌毒素对油菜胚根和胚芽生长尧幼苗致萎性尧细胞 膜透性尧叶绿素含量尧根系活力和幼苗生长的影响。结果表明院根肿菌毒素具有明显的生物活性、能够抑制油菜胚根 和胚芽的生长、且随处理时间的延长和处理浓度的增加、幼苗萎蔫级数逐渐增加。毒素的作用可使油菜细胞膜透性 增加、叶绿素含量和根系活力下降、其中叶绿素b 的含量随处理时间的延长表现为先上升后下降的趋势、但仍低于 对照。油菜幼苗的株高和主根长随毒素浓度的提高均呈逐渐下降的趋势、在85%和100%毒素浓度胁迫下、油菜幼苗 株高及主根长均显著低于对照、说明植株的生长受到明显抑制。     

莲子草假隔链格孢毒素的致病机理研究

就莲子草假隔链格孢(Nimbya alternantherae)毒素Vuculic acid对空心莲子草(Alligaror alternanthera)的致病机理进行了研究.分别用不同含量的毒素溶液处理空心莲子草离体叶片,测定其对叶片组织细胞膜透性、丙二醛(MDA)含量、细胞内Na 、K 渗漏量以及过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)和过氧化氢酶(CAT)活性的影响.结果表明,空心莲子草叶片组织浸出液的相对电导率随毒素含量的增高和处理时间的增加而增大;Na 的渗漏量高于对照;叶片组织MDA的含量也高于对照;空心莲子草叶片组织内CAT和POD活性在处理前、中期(1～6 h),均随时间的延长呈上升趋势,但酶活性都低于对照;APX活性高于对照.