Different protofilament-dependence of the microtubule binding between MAP2 and MAP4

To see a molecular basis of the difference in the microtubule binding between MAP2 and MAP4, we compared the binding of them onto microtubule and Zinc-sheet in the presence of various concentrations of NaCl. The Zinc-sheet is the lateral association of protofilaments arranged in an antiparallel fashion with alternatively exposed opposite surfaces, so that binding requiring adjacent protofilaments is restricted. While the salt-dependence of the MAP2 desorption was not altered between these tubulin polymers, MAP4 dissociated from Zinc-sheet at lower concentrations of NaCl than from microtubule. These results suggest that single protofilament is sufficient for microtubule binding of MAP2 as observed by Al-Bassam et al. [J. Cell Biol. 157 (2002) 1187], but MAP4 appeared to interact with adjacent protofilaments during microtubule-binding. Weakened binding on Zinc-sheets was also observed in the projection domain-deletion mutants of MAP4, so that the difference in the protofilament-dependence would lie in the relatively conserved microtubule-binding domain.     

Effect of taurine on cholesterol metabolism in hamsters: up-regulation of low density lipoprotein (LDL) receptor by taurine

The effects of taurine on hepatic cholesterol metabolism were investigated in hamsters fed a high-fat diet or normal chow. Two weeks-treatment of taurine at 1% in drinking water prevented high-fat diet-induced increase in cholesterol levels of serum and liver. The decrease in serum cholesterol by taurine was due to decrease in non-HDL cholesterols. A similar tendency was noted in serum and liver cholesterol levels of hamsters fed a normal diet. In hamsters fed a high-fat diet, taurine prevented elevation in hepatic activity of acyl-CoA:cholesterol acyltransferase (ACAT) and increased the activity of cholesterol 7alpha-hydroxylase. Taurine also increased cholesterol 7alpha-hydroxylase activity in hamsters fed normal chow. Studies on liver membranes revealed that taurine increased 125I-labeled LDL binding by 52% and 58% in hamsters fed either a normal chow or high-fat diet, respectively. Furthermore, LDL kinetic analysis showed that taurine intake resulted in significant faster plasma LDL fractional catabolic rates (FCR). These results suggest that taurine elevates hepatic LDL receptor and thereby decreases serum cholesterol levels, an event which may be the result of hepatic cholesterol depletion as a consequence of increased bile acid synthesis via enhancement of cholesterol 7alpha-hydroxylase activity. Thus, up-regulation of the LDL receptor and subsequent increase in receptor- mediated LDL turnover may be a key event in the cholesterol-lowering effects of taurine in hamsters.     

A long CAG repeat in the mouse Sca1 locus replicates SCA1 features and reveals the impact of protein solubility on selective neurodegeneration

A single nicotine exposure increases dopamine levels in the mesolimbic reward system for hours, but nicotine concentrations experienced by smokers desensitize nAChRs on dopamine neurons in seconds to minutes. Here, we show that persistent modulation of both GABAergic and glutamatergic synaptic transmission by nicotine can contribute to the sustained increase in dopamine neuron excitability. Nicotine enhances GABAergic transmission transiently, which is followed by a persistent depression of these inhibitory inputs due to nAChR desensitization. Simultaneously, nicotine enhances glutamatergic transmission through nAChRs that desensitize less than those on GABA neurons. The net effect is a shift toward excitation of the dopamine reward system. These results suggest that spatial and temporal differences in nicotinic receptor activity on both excitatory and inhibitory neurons in reward areas coordinate to reinforce nicotine self-administration.     

Use of a biomimetic chromatographic stationary phase for study of the interactions occurring between inorganic anions and phosphatidylcholine membranes

A liquid chromatographic method for the study of ion-membrane interactions is reported. A phosphatidylcholine biomimetic stationary phase was established by loading dimyristoylphosphatidylcholine (DMPC) onto a reversed-phase octadecylsilica packed column. This column was then used to study the interaction of some inorganic anions with the stationary phase by UV and conductivity detection. Ten inorganic anions were selected as model ions and were analyzed with the proposed chromatographic system. Anion-DMPC interactions of differing magnitudes were observed for all of the model anions. Perchlorate-DMPC interactions were strongest, followed by thiocyanate-DMPC, iodide-DMPC, chlorate-DMPC, nitrate-DMPC, bromide-DMPC, chloride-DMPC, fluoride-DMPC, and then sulfate-DMPC. Cations in the eluent, especially H(+) ions and divalent cations such as Ca(2+), showed strong effects on anion-DMPC interactions. The chromatographic data suggest that DMPC interacts with both the anions and the cations. Anion-DMPC interactions were dependent on the surface potential of the stationary phase: at low surface potentials anion-DMPC interactions were predominantly solvation dependent in nature whereas at more positive surface potentials anion-DMPC interactions were predominantly electrostatic in nature. Cation-DMPC interactions served to raise the surface potential, causing the anion-DMPC interactions to vary from solvation dependent to electrostatic. The chromatographic data were used to provide quantitative estimates of the enthalpies of the anion-DMPC interactions.     

Innate apoptosis of human B lymphoblasts transformed by Epstein-Barr virus: modulation by cellular immortalization and senescence

B-lymphoblastoid cell lines (LCLs) transformed by Epstein-Barr virus have a phenotype corresponding to activated B-lymphoblasts. Although they are widely used as models in various biological and medical studies, their innate morphological differentiation and apoptosis has been little studied. We report here that a large proportion of LCL cells spontaneously differentiate into smaller lymphoid cells which ultimately undergo apoptosis during conventional cell culture. Two distinct types of apoptosis with some intermediate types exist: type 1 apoptosis in small and medium-size cells with shrunken nuclei having heavily condensed chromatin in the whole nucleus region accompanied by relatively large internucleosomally fragmented DNA (above 2 kbp); type 2 apoptosis in large lymphoblasts with extremely lobulated nuclei having chromatin condensation beneath the nuclear membrane alone accompanied by smaller internucleosomally fragmented DNA (below 2 kbp). Type 1 apoptotic cells were far more numerous than type 2 apoptotic cells. The incidence of type 1 apoptosis was suppressed by cellular immortalization and was extremely stimulated at the end of the lifespan (crisis). These results provide essential information for us to use LCLs for various biological and medical studies including cellular immortalization, tumorigenesis and senescence.     

Excessive increase of serum interleukin 6 jeopardizes host defense against multi-bacterial infection

Serum interleukin 6 (IL-6) is elevated among patients who have undergone surgery, trauma, and thermal injury. It is well known that the greater the increase of serum IL-6, the higher the incidence of post-injury morbidity and mortality is. However, it has not been determined whether the physiological effects of IL-6 increase the rate of morbidity and mortality or if IL-6 is just a bystander that only indicates the severity of the injury. To elucidate this, we planned to investigate the effect of IL-6 on a multi-bacterial infection, one of the most frequent post-injury complications. CDF1 male mice were administered recombinant human IL-6 (hIL-6) continuously at a dose of 0, 1, or 10 microg/day. The mice then underwent cecal ligation without puncture that induced slow multi-bacterial infection. The survival rate of mice receiving 10 microg/day of hIL-6 was significantly lower (38.5%) than the rate of those receiving 0 (83.3%) or 1 (92.3%) microg/day of hIL-6. The result of this study showed that only excessive increases in serum IL-6, to levels that were observed among patients who underwent severe injury or extensive surgery with high incidence of post-injury infection, jeopardize the host's defense against bacterial infection.     

Glycosidase-catalyzed deoxy oligosaccharide synthesis. Practical synthesis of monodeoxy analogs of ethyl beta-thioisomaltoside using Aspergillus niger alpha-glucosidase

Enzymatic transglycosylation using four possible monodeoxy analogs of p-nitrophenyl alpha-D-glucopyranoside (Glc alpha-O-pNP), modified at the C-2, C-3, C-4, and C-6 positions (2D-, 3D-, 4D-, and 6D-Glc alpha-O-pNP, respectively), as glycosyl donors and six equivalents of ethyl beta-D-thioglucopyranoside (Glc beta-S-Et) as a glycosyl acceptor, to yield the monodeoxy derivatives of glucooligosaccharides were done. The reaction was catalyzed using purified Aspergillus niger alpha-glucosidase in a mixture of 50 mM sodium acetate buffer (pH 4.0)/CH3CN (1:1 v/v) at 37 degrees C. High activity of the enzyme was observed in the reaction between 2D-Glc alpha-O-pNP and Glc beta-S-Et to afford the monodeoxy analogs of ethyl beta-thiomaltoside and ethyl beta-thioisomaltoside that contain a 2-deoxy alpha-D-glucopyranose moiety at their glycon portions, namely ethyl 2-deoxy-alpha-D-arabino-hexopyranosyl-(1,4)-beta-D-thioglucopyranoside and ethyl 2-deoxy-alpha-D-arabino-hexopyranosyl-(1,6)-beta-D-thioglucopyranoside, in 6.72% and 46.6% isolated yields (based on 2D-Glc alpha-O-pNP), respectively. Moreover, from 3D-Glc alpha-O-pNP and Glc beta-S-Et, the enzyme also catalyzed the synthesis of the 3-deoxy analog of ethyl beta-thioisomaltoside that was modified at the glycon alpha-D-glucopyranose moiety, namely ethyl 3-deoxy-alpha-D-ribo-hexopyranosyl-(1,6)-beta-D-thioglucopyranoside, in 23.0% isolated yield (based on 3D-Glc alpha-O-pNP). Products were not obtained from the enzymatic reactions between 4D- or 6D-Glc alpha-O-pNP and Glc beta-S-Et.