Synthesis of aminoethyl glycosides of the carbohydrate chains of glycolipids Gb3, Gb4 i Gb5

4-O-Glycosylation of 2-azidoethyl 2,3,6-tri-O-benzoyl-4-O-(2,3,6-tri-O-benzoyl-beta-D-galactopyranosyl)-beta- D-glucopyranoside with ethyl 2,3,4,6-tetra-O-benzyl- and ethyl 3-O-acetyl-2,4,6-tri-O-benzyl-1-thio-alpha-D-galactopyranoside in the presence of methyl trifluoromethanesulfonate led to trisaccharide 2-azidoethyl (2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl)-(1-->4)- (2,3,6-tri-O-benzoyl-beta-D-galactopyranosyl)-(1-->4)2,3,6-tri-O- benzoyl-beta-D-glucopyranoside and its 3"-O-acetylated analogue, 2-azidoethyl (3-O-acetyl-2,4,6-tri-O-benzyl- alpha-D-galactopyranosyl)-(1-->4)-(2,3,6-tri-O-benzoyl-beta-D- galactopyranosyl)-(1-->4)-2,3,6-tri-O-benzoyl-beta-D-glucopyranoside, in yields of 85 and 83%, respectively. Deacetylation of the latter compound and subsequent glycosylation with 4-trichloroacetamidophenyl 3,4,6-tri-O-acetyl-2-deoxy-1-thio-2-trichloroacetamido-beta-D- galactopyranoside and 4-trichloroacetamidophenyl 4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O- acetyl-beta-D-galactopyranosyl)-1-thio-2-trichloroacetamido-beta-D- galactopyranoside in dichloromethane in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid resulted in the corresponding selectively protected derivatives of tetrasaccharide GalNAc(beta 1-->3)Gal(alpha 1-->4)Gal(beta 1-->4)Glc beta-OCH2CH2N3 and pentasaccharide Gal(beta 1-->3)GalNAc(beta 1-->3)Gal(alpha 1-->4)Gal(beta 1-->4)Glc beta-OCH2CH2N3 in 88 and 73% yields, respectively. Removal of O-protecting groups, substitution of acetyl group for N-trichloroacetyl group, and reduction of the aglycone azide group resulted in the target 2-aminoethyl globo-tri-, -tetra-, and -pentasaccharide, respectively.     

Characterization of the elongating alpha-D-mannosyl phosphate transferase from three species of Leishmania using synthetic acceptor substrate analogues

Leishmania express lipophosphoglycans and proteophosphoglycans that contain Galbeta1-4Manalpha1-P phosphosaccharide repeat structures assembled by the sequential addition of Manalpha1-P and betaGal. The synthetic acceptor substrate Galbeta1-4Manalpha1-P-decenyl and a series of analogues were used to probe Leishmania alpha-D-mannosyl phosphate transferase activity. We show that the activity detected with Galbeta1-4Manalpha1-P-decenyl is the elongating alpha-D-mannosyl phosphate transferase associated with lipophosphoglycan biosynthesis (eMPT(LPG)). Differences in the apparent K(m) values for the donor and acceptor substrates were found using L. major, L. mexicana, and L. donovani promastigote membranes, but total activity correlated with the number of lipophosphoglycan repeats. Further comparisons showed that lesion-derived L. mexicana amastigotes, that do not express lipophosphoglycan, lack eMPT(LPG) and that nondividing L. major metacyclic promastigotes contain 5-fold less eMPT(LPG) activity than dividing procyclic promastigotes. The fine specificity of promastigote eMPT(LPG) activity was determined using 24 synthetic analogues of Galbeta1-4Manalpha1-P-decenyl. The three species gave similar results: the negative charge of the phosphodiester and the C-6 hydroxyl of the alphaMan residue are essential for substrate recognition, the latter most likely acting as a hydrogen bond acceptor. The C-6' hydroxyl of the betaGal residue is required for substrate recognition as well as for catalysis. The rate of Manalpha1-P transfer declines with increasing acceptor substrate chain length. The presence of a monosaccharide substituent at the C-3 position of the terminal betaGal residue abrogates Man-P transfer, showing that chain elongation must precede side chain modification during lipophosphoglycan biosynthesis. In contrast, substitution of the penultimate phosphosaccharide repeat does not abrogate transfer but is slightly stimulatory in L. mexicana and inhibitory in L. major.     

Calmodulin-peptide interactions: apocalmodulin binding to the myosin light chain kinase target-site

Noncovalent binding of the synthetic peptide RS20 to calmodulin in the presence of calcium was confirmed by electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry to form a complex with a 1:1:4 calmodulin/RS20/calcium stoichiometry. There was no evidence for formation of a calmodulin-RS20-Ca(2) species. The absence of calmodulin-RS20-Ca(2) would be consistent with models in which the two globular domains are coupled functionally. There was evidence that calmodulin, RS20-calmodulin without associated calcium, and calmodulin-RS20-Ca(4) existed together in solution, whereas calmodulin-calcium complexes were absent. It is proposed that calcium binding to form the calmodulin-RS20-Ca(4) complex occurs after an initial RS20-calmodulin binding event, and serves to secure the target within the calmodulin structure. The binding of more than one RS20 molecule to calmodulin was observed to induce unfolding of calmodulin.     

Effect of serotonin on isolated cells with the various functionality from the lamprey spinal cord

The differential actions of 5-hydroxytryptamine (5-HT) (100 microM) were investigated on isolated motoneurons, interneurons, and primary sensory neurons from the lamprey spinal cord using patch-clamp techniques. Application of 5-HT did not evoke membrane currents in any of the spinal neurons tested (n = 62). However, in most motoneurons and interneurons (15 of 18), 5-HT produced a small depolarization (2-6 mV), which was not accompanied by a change in input resistance. In the remaining motoneurons and interneurons (3 of 18), 5-HT induced a large depolarization (up to 10-20 mV) and a decrease in input resistance of 20-60%. In most sensory neurons (dorsal sensory cells, DSCs), 5-HT evoked a short-lasting, low-amplitude depolarization, followed by a long-lasting hyperpolarization of 2-7 mV. The DSCs showed no significant change in input resistance to 5-HT application (n = 8). Spike afterpolarization were also differentially modulated by 5-HT. In motoneurons and interneurons, 5-HT decreased the amplitude of the afterhyperpolarization following the action potential while increasing the amplitude of the after depolarization. In the DSCs, no significant effect of 5-HT on spike afterpolarization was observed. 5-HT differentially modulated the current induced by application of N-methyl-D-aspartate (NMDA). In motoneurons and interneurons, 5-HT enhanced NMDA-evoked current, while in DSCs, 5-HT decreased this current. These results demonstrate that 5-HT differentially modulates the activity of functionally different groups of spinal neurons. In motoneurons and interneurons, 5-HT enhances excitation by inducing depolarization and decreasing the afterhyperpolatization, while NMDA currents are enhanced. These effects facilitate the appearance of rhythmic discharges in these cells in the presence of NMDA. In primary dorsal sensory cells, 5-HT enhances inhibition by hyperpolarizing the cells and depressing NMDA currents. These differential effects are presumably mediated by different types of 5-HT receptors on these classes of spinal neurons.     

Quantitative regularities for clinical manifestations of radiation injury in large-sized laboratory animals exposed to supralethal radiation doses Gamma-neutron and electron biological effectiveness as influenced by exposure conditions and dose distribution in the animal body

The damaging effect of gamma-neutron radiation over a wide neutron-energy range, with average values of 0.37 and 1.2 MeV, and that of electrons with an average electron energy of 25 MeV have been compared in dogs and two monkey species exposed to a broad range of supralethal doses. An analysis of absorbed dose distribution in critical organs and systems has shown the highest effect of gamma-neutron radiation with an average neutron energy of 1.2 MeV. With severity of early clinical manifestations of damage as a criterion, electrons have appeared the most effective. The radiosensitivity of animals grew in the order as follows: dog-->M. fascicularis-->P. hamadryas.     

Centrosomal Chk2 in DNA damage responses and cell cycle progession

Two major control systems regulate early stages of mitosis: activation of Cdk1 and anaphase control through assembly and disassembly of the mitotic spindle. In parallel to cell cycle progression, centrosomal duplication is regulated through proteins including Nek2. Recent studies suggest that centrosome-localized Chk1 forestalls premature activation of centrosomal Cdc25b and Cdk1 for mitotic entry, whereas Chk2 binds centrosomes and arrests mitosis only after activation by ATM and ATR in response to DNA damage. Here, we show that Chk2 centrosomal binding does not require DNA damage, but varies according to cell cycle progression. These and other data suggest a model in which binding of Chk2 to the centrosome at multiple cell cycle junctures controls co-localization of Chk2 with other cell cycle and centrosomal regulators.Key words: Chk2, centrosome, checkpoint, DNA damage, wild type, kinase-defective     

Microtubule-binding proteins CLASP1 and CLASP2 interact with actin filaments

Cell morphogenesis requires dynamic communication between actin filaments and microtubules which is mediated, at least in part, by direct structural links between the two cytoskeletal systems. Here, we examined interaction between the CLIP-associated proteins (CLASP) CLASP1 and CLASP2, and actin filaments. We demonstrate that, in addition to a well-established association with the distal ends of microtubules, CLASP2alpha co-localizes with stress fibers, and that both CLASP1alpha and CLASP2alpha co-immunoprecipitate with actin. GFP-CLASP2alpha exhibits retrograde flow in the lamellipodia of Xenopus primary fibroblasts and in the filopodia of Xenopus spinal cord neurons. A deletion mapping analysis reveals that both the microtubule-binding domain of CLASP2 (which is homologous between all CLASPs) and the N-terminal dis1/TOG domain of CLASP2alpha (which is homologous between alpha isoforms) possess actin-binding activity. Fluorescence resonance energy transfer experiments demonstrate significant energy transfer between YFP-CLASP2alpha and CFP-actin. Our results indicate that CLASPs function as actin/microtubule crosslinkers in interphase cells. We propose that CLASPs facilitate recognition of actin filaments by the plus ends of growing microtubules at the initial stages of actin-microtubule interaction. Cell Motil.     

Ebola hemorrhagic fever: Properties of the pathogen and development of vaccines and chemotherapeutic agents

Molecular Biology - Ebola hemorrhagic fever (EHF) epidemic currently ongoing in West Africa is not the first among numerous epidemics in the continent. Yet it seems to be the worst EHF epidemic...     

20S proteasomal degradation of ornithine decarboxylase is regulated by NQO1

Ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of polyamines, is a very labile protein. ODC is a homodimeric enzyme that undergoes ubiquitin-independent proteasomal degradation via direct interaction with antizyme, a polyamine-induced protein. Binding of antizyme promotes the dissociation of ODC homodimers and marks ODC for degradation by the 26S proteasomes. We describe here an alternative pathway for ODC degradation that is regulated by NAD(P)H quinone oxidoreductase 1 (NQO1). We show that NQO1 binds and stabilizes ODC. Dicoumarol, an inhibitor of NQO1, dissociates ODC-NQO1 interaction and enhances ubiquitin-independent ODC proteasomal degradation. We further show that dicoumarol sensitizes ODC monomers to proteasomal degradation in an antizyme-independent manner. This process of NQO1-regulated ODC degradation was recapitulated in vitro by using purified 20S proteasomes. Finally, we show that the regulation of ODC stability by NQO1 is especially prominent under oxidative stress. Our findings assign to NQO1 a role in regulating ubiquitin-independent degradation of ODC by the 20S proteasomes.