Enatioselective[2 2 2] Cycloaddition as A Synthetic Tool

1 Results Transition metal-catalyzed [2 2 2] cycloaddition is one of the most efficient protocols for the construction of six-membered ring system.Our group has comprehensively studied various types of highly enantioselective [2 2 2] cycloaddition for the synthesis of chiral cycloadducts; we already reported an iridium-catalyzed intermolecular [2 2 2] cycloaddition between α,ω-diynes,having various tethers and substituents on the alkyne termini,and monoalkynes,possessing oxygen or/and nitrogen functiona...     

Poly(ADP-ribose) is required for spindle assembly and structure

The mitotic spindle is typically thought of as an array of microtubules, microtubule-associated proteins and motors that self-organizes to align and segregate chromosomes. The major spindle components consist of proteins and DNA, the primary structural elements of the spindle. Other macromolecules including RNA and lipids also associate with spindles, but their spindle function, if any, is unknown. Poly(ADP-ribose) (PAR) is a large, branched, negatively charged polymeric macromolecule whose polymerization onto acceptor proteins is catalysed by a family of poly(ADP-ribose) polymerases (PARPs). Several PARPs localize to the spindle in vertebrate cells, suggesting that PARPs and/or PAR have a role in spindle function. Here we show that PAR is enriched in the spindle and is required for spindle function--PAR hydrolysis or perturbation leads to rapid disruption of spindle structure, and hydrolysis during spindle assembly blocks the formation of bipolar spindles. PAR exhibits localization dynamics that differ from known spindle proteins and are consistent with a low rate of turnover in the spindle. Thus, PAR is a non-proteinaceous, non-chromosomal component of the spindle required for bipolar spindle assembly and function.     

Repeat I of the dihydropyridine receptor is critical in determining calcium channel activation kinetics.

Membrane depolarization causes many kinds of ion channels to open, a process termed activation. For both Na+ channels and Ca2+ channels, kinetic analysis of current has suggested that during activation the channel undergoes several conformational changes before reaching the open state. Structurally, these channels share a common motif: the central element is a large polypeptide with four repeating units of homology (repeats I-IV), each containing a voltage-sensing region, the S4 segment. This suggests that the distinct conformational transitions inferred from kinetic analysis may be equated with conformational changes of the individual structural repeats. To investigate the molecular basis of channel activation, we constructed complementary DNAs encoding chimaeric Ca2+ channels in which one or more of the four repeats of the skeletal muscle dihydropyridine receptor are replaced by the corresponding repeats derived from the cardiac dihydropyridine receptor. We report here that repeat I determines whether the chimaeric Ca2+ channel shows slow (skeletal muscle-like) or rapid (cardiac-like) activation.     

CD43, a molecule defective in Wiskott-Aldrich syndrome, binds ICAM-1.

THE protein CD43 (also known as sialophorin, leukosialin, large sialoglycoprotein or gp115) is expressed on the surface of T lymphocytes, monocytes, neutrophils, platelets and some B lymphocytes. Expression of CD43 is deficient and/or defective in the X-chromosome-linked immunodeficiency disorder Wiscott-Aldrich syndrome, suggesting that CD43 might have a role in T-cell activation. We have shown that expression of human CD43 in an HLA-DR-specific murine T-cell hybridoma enhances the antigen-specific response to stimulation by the human lymphoblastoid cell line Daudi, and that Daudi cells bind specifically to purified immobilized CD43. These data indicate that the specific interaction of CD43 with a ligand on the surface of Daudi cells might contribute to T-cell activation. Here we report evidence that intercellular adhesion molecule-1 (ICAM-1, or CD54), is a ligand for CD43.     

Left-handed Z-DNA is induced by supercoiling in physiological ionic conditions

In physiological ionic conditions (200 mM NaCl), the (dC-dG)16 and (dC-dG)13 blocks in plasmid pRW751 are in a left-handed state when the negative superhelical density of the plasmid is greater than 0.972. As the salt concentration decreases or when (dmC-dG) sequences are present, less negative supercoiling is required to induce the right- to left-handed DNA transition. Furthermore, the single strand-specific nuclease, S1, recognizes and cleaves aberrant structural features at the junction between neighbouring right- and left-handed DNA regions.     

Amplification of immunoglobulin lambda constant genes in populations of wild mice

The lambda immunoglobulin light chain (Ig lambda) locus of BALB/c inbred mice consists of two variable region gene segments (V lambda)1-3, and four constant region gene segments (C lambda)1,2,4,5. Each C lambda gene segment is associated with a unique joining segment (J lambda)2,4-7, and they are organized in two paired units, J3C3-J1C1 and J2C2-J4C4 (refs 4, 8). Using cDNA probes specific for C lambda 1 and C lambda 2 (ref. 9) we have analysed the genomic organization of the C lambda gene segments in wild-derived and inbred strains of mice. Although Southern blots of the genomic DNA of inbred mice show a constant pattern of hybridization, wild-derived mice show a high degree of variation in the number, size and intensity of hybridizing fragments. We have now found that, per haploid genome, mice of a Mus musculus musculus stock isolated from Sladeckovce, Czechoslovakia (CzII) have at least 12 C lambda segments, and mice of a Mus musculus domesticus stock 'Centreville Lights' from Centreville, Maryland (CL) have at least 8 C lambda segments. There appears to have been relatively recent amplifications of the C lambda gene segments in wild mice.     

Tests of the helix dipole model for stabilization of alpha-helices

Charged groups play a critical role in the stability of the helix formed by the isolated C-peptide (residues 1-13 of ribonuclease A) in aqueous solution. One charged-group effect may arise from interactions between charged residues at either end of the helix and the helix dipole. We report here that studies of C-peptide analogues support the helix dipole model, and provide further evidence for the importance of electrostatic interactions not included in the Zimm-Bragg model for alpha-helix formation.     

Stimulation of specific GTP binding and hydrolysis activities in lymphocyte membrane by interleukin-2

Interleukin-2 (IL-2) is a polypeptide growth factor which stimulates the proliferation and differentiation of T lymphocytes. The receptor for IL-2 is expressed on activated T lymphocytes, cloned IL-2 dependent cells and several other cell types. Analysis of the primary structure and of immune-precipitated receptor suggests that this molecule has no intrinsic signal transduction function, unlike other growth factors. IL-2 interaction with a high affinity receptor has been shown, however, to activate the calcium/phospholipid-dependent protein kinase C (PK-C) presumably via phosphoinositide hydrolysis. Members of a family of closely related guanine nucleotide binding proteins (G proteins) regulate a diverse group of metabolic events. Two of them, Gs and Gi, stimulate and inhibit adenylate cyclase activity respectively, and other G proteins are involved in diverse signal transduction system. Another member, Go, has no known function and activation of phospholipase C has been attributed to the action of an unidentified G protein, Gp. Since it has been observed that IL-2 inhibits the catalytic activity of adenylate cyclase and that agents such as PGE2 which stimulate adenylate cyclase activity inhibit the lymphoproliferative response to IL-2, association of GTP binding proteins with IL-2 signal transduction was investigated. In this report we describe for the first time the participation of a GTP binding protein in the action of a polypeptide growth factor, interleukin-2.