Highly Selective Diphoshinoamine/Cr(III) Catalysts for Ethylene Tetramerization

Two novel diphoshinoamine ligands have been synthesized. Combination of Cr（Ⅲ） and methylaluminoxane（MAO） generated active catalytic system which can catalyze tetramerization of ethylene with high catalytic activity up to 2.5×10^6 g/mol Cr.h and high selectivity to produce 1-octene （Cs in products is being 89.80 wt%）.

Preparation and Catalytic Performance of Silica-Supported Cr(acac)_3/PNP for Ethylene Tetramerization

Chromium acetylacetonate and bis(diphenylphosphino)isopropylamine were coordinated in situ and supported on methylaluminoxane-modified silica. The catalyst structure and effects of reaction temperature, reaction pressure and Al/Cr molar ratio on ethylene tetramerization were investigated in detail. Chromium was uniformly and firmly immobilized on the support and could not be leached off by methylaluminoxane. The supported catalyst, upon being activated with methylaluminoxane, exhibited catalytic activity of 1.70×107 g/(mol Cr·h) for ethylene tetramerization to form 1-octene at a reaction temperatures of 80 ℃, a pressure of 2.0 MPa and an Al/Cr molar ratio of 300. The supported catalyst presented a good tolerance to high temperature.

自身免疫糖尿病细胞免疫学研究进展

自身免疫糖尿病是一种T细胞介导的胰岛 β细胞选择性破坏的自身免疫病。主要组织相容性复合物 (ma jorhistocompabilitycomplex ,MHC)限制性中枢及外周T细胞自身耐受丧失 ,细胞免疫调节失衡 ,胰岛自身抗原反应性T细胞克隆活化 ,Th1细胞及其细胞因子释放占优势 ,将启动、维持和加速自身免疫性胰岛炎 ,导致糖尿病发生。应用ELISPOT和可溶性MHC -肽四聚体技术并解决T细胞分析的标准化问题 ,将显著促进自身免疫糖尿病与细胞免疫学研究的发展。

KCTD-12 inhibits the in vitro proliferation and invasion of gastrointestinal stromal tumor cells: the experimental study

Objective:To study the effects of potassium channel tetramerization domain-containing 12 (KCTD-12) overexpression on in vitro proliferation and invasion of gastrointestinal stromal tumor cells.Methods:Gastrointestinal stromal tumor cell lines were cultured and randomly divided into KCTD-12 overexpression group and NC overexpression group that were transfected with KCTD-12 overexpression plasmid and negative control plasmid respectively. 24 h after transfection, the expression of proliferation genes, apoptosis genes, PI3K and p38MAPK signaling pathway molecules as well as invasion genes in cells were detected. Results: Ki-67, SCIN, Bcl-2, p-PI3K, p-AKT, p-p38MAPK, CD146, PAR-2, SDF-1 and CXCR4 expression in KCTD-12 overexpression group were significantly lower than those in NC overexpression group while Bax, Caspase-3, Caspase-7, Caspase-9 and p-FOXO1 expression were significantly higher than those in NC overexpression group.Conclusion:KCTD-12 can inhibit the in vitro proliferation and invasion of gastrointestinal stromal tumor cells.

A New Stilbene Tetramer from Caragana rosea

Cararosinol A, a new stilbene tetramer, was isolated from Caragana rosea. Its structure has been established on the basis of spectroscopic evidence.

A New Isopropenyl Benzofuran-type Tetramer from Ligularia stenocephala

A new isopropenyl benzofuran-type tetramer was isolated from the roots of ligularia stenocephala and its structure was established by spectroscopic methods.

Hydrothermal Assembly and Structural Characterization of an Octamolybdate Supported Copper (Ⅰ) Tetramer: [Cu_2(1,10-phen)_2(4,4′-bpy)]_2[Mo_8O_(26)]·4H_2O

A hydrothermal reaction of copper acetate with ammonium molybdate, 4,4-bpy (4,4-bipyridine) and 1,10-phen (1,10-phenanthroline) led to the formation of brown crystals of [Cu2(1,10-phen)2(4,4-bpy)]2 [Mo8O26]4H2O 1. Single-crystal X-ray analysis has revealed that 1 (C68H56N12O30Cu4Mo8) crystallizes in the triclinic system, space group P with a = 11.270(3), b = 13.113(6), c = 13.906(3) ? = 103.33(4), b = 98.54(2), g = 101.29(2)? V = 1920.1(1) ?3, Mr = 2542.93, Z = 1, Dc = 2.199 g/cm3, m = 2.435 mm-1, F(000) = 1240, the final R = 0.0445, wR = 0.1082 and S = 1.021 for 5052 observed reflections with I >2s(I). It consists of copper (Ⅰ) tetramer units and -[Mo8O26]4- anions, which are further attached into a three-dimensional framework through hydrogen bonding and - stacking interactions.

Navigating the dynamic landscape of alpha-synuclein morphology: a review of the physiologically relevant tetrameric conformation

N-acetylatedα-synuclein(αSyn)has long been established as an intrinsically disordered protein associated with a dysfunctional role in Parkinson’s disease.In recent years,a physiologically relevant,higher order conformation has been identified as a helical tetramer that is tailored by buried hydrophobic interactions and is distinctively aggregation resistant.The canonical mechanism by which the tetramer assembles remains elusive.As novel biochemical approaches,computational methods,pioneering purification platforms,and powerful imaging techniques continue to develop,puzzling information that once sparked debate as to the veracity of the tetramer has now shed light upon this new counterpart inαSyn neurobiology.Nuclear magnetic resonance and computational studies on multimericαSyn structure have revealed that the protein folding propensity is controlled by small energy barriers that enable large scale reconfiguration.Alternatively,familial mutations ablate tetramerization and reconfigure polymorphic fibrillization.In this review,we will discuss the dynamic landscape ofαSyn quaternary structure with a focus on the tetrameric conformation.

Resveratrol Tetramers from the Roots of Ampelopsis sinica

A new resveratrol tetramer, sinicin A was isolated from the roots of Ampelopsis sinica, with four known tetramers: vitisin A, cis-vitisin B, ampelopsin H and hopeaphenol. The structure and stereochemistry of sinicin A have been established on the basis of 1D and 2D NMR spectroscopic techniques.

A Novel Zn(Ⅱ)Complex with 1D Supramolecular Water Tape Formed by Cyclic Tetrameric Water Clusters

A new mixed-ligand Zn（II） complex, [Zn（4,4′-bipy）2（H2O）4]-2ANS·6H2O （1, 4,4′- bipy = 4,4′-bipyridine, HANS = 2-aminonaphthalene-l-sulfonic acid）, has been isolated and structurally characterized by single-crystal X-ray diffwaction, FT-IR spectrum, TG and elemental analysis. It crystallizes in the monoclinic system, space group P2 1/c with a = 12.4852（8）, b = 18.3163（12）, c = 10.9707（7） A, β = 114.2600（10）°, V= 2287.3（3） A3, Dc = 1.455 g/cm3, Mr = 1002.37, Z = 2, F（000） = 1048,μ = 0.704 mm＂1, the final R = 0.0408 and wR = 0.962 for 4029 observed reflections with I 〉 2σ（I）. Interestingly, an unusual one-dimensional （1D） water tape with cyclic tetrameric water clusters can be observed in 1, which are further trapped via Zn-O coordination bonds exhibiting a 2D Zn（Ⅱ）-water layer. These 2D Zn（Ⅱ）-water layers are stacked together into a 3D interdigitated supramolecular architecture via weak π…π interactions, in which free ANS anions are tightly filled by hydrogen-bonding interactions. Thus, π…π and classical hydrogen-bonding interactions are fotmd as main driving forces to stabilize the 2D Zn（Ⅱ）-water layers.

Construction of HLA/Peptide Tetramer with Peptide-Linked β_2 Microglobulin

Analysis of the frequency of antigen-specific cytotoxic T lymphocytes (CTLs) ex vivo is largely dependent on the use of MHC/peptide tetramers. However, the latter reagents have not been widely available, most likely because of their costly and time-consuming production. In this report we utilized an economic strategy to construct HLA/peptide tetramers with recombinant peptide-linked β2 microglobulin (β2m). The HLA-A2-restricted, melanoma antigen MARTI-derived pep- tide MART127-35( AAGIGILTV) was fused to the N terminus of human β2m through a 15-amino acid (aa)-long linker before being refolded with the recombinant biotinylated HLA-A2 heavy chain ectodomain. The resulted 2-component (2C) monomer was then tetramerized with phycoerythin-labeled streptavidin. The experimental result showed that the 2C HLA-A2/ MART127-35 monomer was shown to bind to the HLA class complex-specific monoclonal antibody W6/32 and the HLA-A2/ MART127-35 complex-specific single chain antibody fragment (scFv) 8.3, suggesting the correctness of its specificity. Fur- thermore, the 2C HLA-A2/MART127-35 tetramer detected a specific CD8+ T cell population in HLA-A2-restricted melanoma infiltrating lymphocytes as the conventional 3C HLA-A2/MART127-35 tetramer. The yield of 2C HLA-A2/MART127-35 monomer was 2. 5 times more than that of the conventional 3C monomer. Taken together, these data indicate that the HLA-A2/ MART127-35 tetramer can be generated conveniently through the use of MART127-35 peptide-β2 m fusion proteins, which can fa- cilitate the monitoring of HLA-A2-restricted, MART1-specific CTL responses in patients with melanoma.

树突状细胞体外刺激对HBV特异性细胞毒T细胞影响的研究

目的探讨通过聚肌胞体外作用树突状细胞后改善慢性乙型肝炎患者树突状细胞功能,并在体外活化自身T细胞获得高频数HBV特异性细胞毒性T细胞(CTL)的方法。方法分离慢性乙型肝炎病人外周血单个核细胞,在粒巨噬细胞集落刺激因子(GM CSF)和白细胞介素4(IL4)的诱导下培养树突状细胞。培养的第7天加入聚肌胞刺激获得成熟树突状细胞,经HBVcore1827肽负载后与自身T淋巴细胞共培养,通过酶联斑点计数法(Elispot)及MHC肽四聚体法(Tetramer)比较病人T细胞未经自身树突状细胞刺激组、经HBVcore1827肽负载的自身树突状细胞刺激组、经聚肌胞促成熟的HBVcore1827肽负载的自身树突状细胞刺激组中HBV特异性的CTL的功能和频数。结果慢性乙型肝炎病人外周血单核细胞体外经GM CSF和IL4诱导可转化为树突状细胞,树突状细胞转化过程中聚肌胞的刺激可显著上调树突状细胞表面分子CD80、CD83的表达(P<0.01),促进树突状细胞的成熟。Elispot法检测分泌IFNγ的CTL的频数病人T细胞未经自身树突状细胞刺激组分泌频数为(9～28)/1×105T细胞,均值16;经HBVcore1827肽负载的自身树突状细胞刺激组频数为(30～67)/1×105T细胞,均值为46;经聚肌胞促成熟的HBVcore1827肽负载的自身树突状细胞刺激组频数为(59～130)/1×105T细胞,均值为98。三组数据?

Construction of Soluble Mamu-B~*1703,a Class I Major Histocompatibility Complex of Chinese Rhesus Macaques,Monomer and Tetramer Loaded with a Simian Immunodeficiency Virus Peptide

Chinese-descent rhesus macaques have become more prevalent for HIV infection and vaccine investigation than Indian-origin macaques. Most of the currently available data and reagents such as major histocompatibility complex （MHC） class I tetramers, however, were derived from Indian-origin macaques due to the dominant use of these animals in history. Although there are significant differences in the immunogenetic background between the two macaque populations, they share a few of common MHC class I alleles. We reported in this study the procedure for preparation of a soluble Mamu-B＊1703 （a MHC class I molecule of Chinese macaques） monomer and tetramer loaded with a dominant simian immunodeficiency virus （SIV） epitope IW9 （IRYPKTFGW） that was identified to be Mamu-B＊1701-restricted in Indian macaques. The DNA fragment encoding the Mamu-B＊1703 extracellular domain fused with a BirA substrate peptide （BSP） was amplified from a previously cloned cDNA and inserted into a prokaratic expression vector. In the presence of the antigenic peptide IW9 and light chain β2-microglobulin, the expressed heavy chain was refolded into a soluble monomer. After biotinylation, four monomers were polymerized as a tetramer by phycoerythrin-conjugated streptavidin. The tetramer, having been confirmed to have the right conformation, was a potential tool for investigation of antigen-specific CD8^＋ T-lymphocytes in SIV vaccine models of Chinese macaques. And our results also suggested that some antigenic peptides reported in Indian-origin macaques could be directly recruited as ligands for construction of Chinese macaque MHC tetramers.

Construction and Functional Test of HLA-A*2402-Peptide Tetramer

HLA-A~*2402 is one of the most frequent HLA-A allele in Asian population.To construct HLA-A~*2402-peptide tetramers,the transmembrane and intracellular segments of HLA-A~*2402 cDNA were replaced with BSP sequence to form a fusion gene of sHLA-A~*2402-BSP.The sHLA-A~*2402-BSP fusion protein and β2m were high-level expressed as insoluble aggregates in E.coli,and refoided to form an HLA-A~*2402-peptide monomeric complex by dilution method in the presence of an antigenic peptide.The HLA-A~*2402-peptide monomeric complex was biotinated and tetramized to prepare HLA-A~*2402-peptide tetramer.Then using the HLA-A~*2402-peptide tetramers to detect antigen-specific cytotoxic T lymphocyte(CTL)induced by artificial antigen presenting cell (aAPC)in vitro.The results showed that HLA-A~*2402-peptide tetramer was prepared correctly,and functional in detecting antigen-specific CTL in vitro,HLA-A~*2402-peptide monomeric and its multimeric complexes are expected to provide a powerful tool for studying mechanisms of immune-related diseases in Asian populations. Cellular & Molecular Immunology.2005;2(2):145-149.

Preparation and Characterization of HLA-A*0201 Tetramer Loaded with IE-1_(316-324) Antigenic Peptide of Human Cytomegalovirus

Major histocompatibility complex （MHC） class I tetramer technology has become the central technique for analyzing antigen-specific CD8^＋ T cell responses and it has been widely used to explore the differentiation and formation of memory CD8^＋ T cells. Previously, a simplified and efficient procedure for preparing high quality HLA-A＊0201 tetramers has been established in our lab and the tetramers loaded with HCMV peptide pp6549s.50a has been successfully applied to investigate HCMV-specific CD8^＋ T cells in Chinese populations. Using similar procedure we reported here the construction of HLA-A＊0201 tetramer loaded with another dominant epitope derived from immediate early （IE）-1 316.324 （VLEETSVML, VLE） of HCMV （A2-VLE） and characterization of this tetramer. After A2-VLE monomer was prepared and purified, its tetramer was then formed at a yield of 83%. The optimized amount of A2-VLE tetramer for staining 100 μl whole blood was 0.5 μg with incubation at 4℃ for 1 h. Furthermore, the dissociation constant of the tetramer binding to the specific CD8^＋ T cells of one HLA-A2^＋ donor was estimated to be 32.7 nmol/L, which is markedly higher than that of MHC monomer. The construction of A2-VLE tetramer provides an alternative choice for investigating HCMV-specific CD8^＋ T cell responses and will deepen our understanding of the differentiation and formation of HCMV-specific memory CD8^＋ T cells. Cellular ＆ Molecular Immunology.

High Level Expression of HLA-A ~*0203-BSP Fusion Protein in Escherichia coli and Construction of Soluble HLA-A ~*0203 Monomer and Tetramer Loaded with Epstein-Barr Virus Peptide

Major histocompatibility complex （MHC） tetramer technology is critical for characterization of antigen-specific T cells. In the present study we reported the successful generation of HLA-A＊0203 tetramer loaded with Epstein- Barr virus EBNA3596-604 peptide （SVRDRLARL, SVR）. Prokaryotic expression vector for the ectodomain of the heavy chain of HLA-A＊0203 fused with a BirA substrate peptide （HLA-A＊0203-BSP） was constructed and the expression conditions of the fusion protein in Escherichia coli （E. coli） were optimized. The fusion protein was highly expressed in inclusion bodies within E. coil It was then refolded in the presence of 132-microglobulin and SVR peptide to form a soluble HLA-A＊0203-SVR monomer. After biotinylation with BirA, the monomer was purified by anion-exchange chromatography and its purity was up to 95%. The tetramer was then formulated by mixing the biotinylated monomer with streptavidin-PE at a ratio of 4：1. Flow cytometry showed that this tetramer could specifically react with antigen-specific CD8^＋ T cells, indicating that it was biologically functional. These results provide a foundation for further characterization of antigen-specific CD8^＋ T cells from HLA-A＊0203 subjects.

Structure of Pro_4H^＋ investigated by infrared photodissociation(IRPD) spectroscopy and theoretical calculations

Combining with electrospray ionization（ESI）mass spectrometry,infrared photodissociation（IRPD）spectroscopy is a powerful method to study structures of cluster ions in the gas phase.In this paper,infrared photodissociation spectrum of Pro_4H~＋in the range of 2700–3600 cm 1was obtained experimentally.Both theoretically predicted spectra of the two most stable isomers of Pro4^（-1） and Pro4^（-2） obtained at the level of M062X/6-31＋G（d,p）are in good consistent with the experimental results.The two isomers have similar structures and close energies.Both of them only consist of zwitterionic units,indicating the strong salt-bridged interactions inside the clusters.And the calculated collision cross section（ccs）of Pro4-1 is found to be very close to the experimental result previously reported.

Preparation and Identification of HLA-A*1101 Tetramer Loading with Human Cytomegalovirus pp65 Antigen Peptide

MHC/peptide tetramer technology has been widely used to study antigen-specific T cells, especially for identifying virus-specific CD8^＋ T cells in humans. The tetramer molecule is composed of HLA heavy chain, β2-microglobulin （β2m）, an antigenic peptide, and fluorescent-labeled streptavidin. To further investigate the HLA-A＊1101-restricted CD8^＋ T cell responses against human cytomegalovirus （HCMV）, we established an approach to prepare HLA-A＊1101 tetramer complexed with a peptide from HCMV. The cDNA encoding HLA-A＊1101 heavy chain was cloned and the prokaryotic expression vector for the ectodomain of HLA-A＊1101 fused with a BirA substrate peptide （HLA-A＊1101-BSP） at its carboxyl terminus was constructed. The fusion protein was highly expressed as inclusion bodies under optimized conditions in Escherichla coli. Moreover, HLA-A＊1101-BSP protein was refolded in the presence of β2m and an HCMV peptide pp6516.24 （GPISGHVLK, GPI）. Soluble HLA-A＊1101-GPI monomer was biotinylated and purified to a purity of 95%, which was subsequently combined with streptavidin to form tetramers at a yield of 〉 80%. The HLA-A＊1101-GPI tetramers could bind to virus-specific CD8^＋ T cells, suggesting soluble HLA-A＊1101-GPI tetramers were biologically functional. This study provides the basis for further evaluation of HLA-A＊1101-restricted CD8^＋ T cell responses against HCMV infection.

Interactions between Transmembrane Helices within Monomers of the Aquaporin AtPIP2;1 Play a Crucial Role in Tetramer Formation

Aquaporin （AQP） is a water channel protein found in various subcellular membranes of both prokaryotic and eukaryotic cells. The physiological functions of AQPs have been elucidated in many organisms. However, understanding their biogenesis remains elusive, particularly regarding how they assemble into tetramers. Here, we investigated the amino acid residues involved in the tetramer formation of the Arabidopsis plasma membrane AQP AtPIP2;1 using extensive amino acid substitution mutagenesis. The mutant proteins V41A/ E44A, F51A/L52A, F87A/191A, F92A/193A, V95A/Y96A, and H216A/L217A, harboring alanine substitutions in the transmembrane （TM） helices of AtPIP2;1 polymerized into multiple oligomeric complexes with a vari- able number of subunits greater than four. Moreover, these mutant proteins failed to traffic to the plasma membrane, instead of accumulating in the endoplasmic reticulum （ER）. Structure-based modeling revealed that these residues are largely involved in interactions between TM helices within monomers. These results suggest that inter-TM interactions occurring both within and between monomers play crucial roles in tetramer formation in the AtPIP2;1 complex. Moreover, the assembly of AtPIP2;1 tetramers is critical for their trafficking from the ER to the plasma membrane, as well as water permeability.