A site in the fourth membrane-associated domain of the N-methyl-D-aspartate receptor regulates desensitization and ion channel gating

The N-methyl-d-aspartate (NMDA) receptor has four membrane-associated domains, three of which are membrane-spanning (M1, M3, and M4) and one of which is a re-entrant pore loop (M2). The M1-M3 domains have been demonstrated to influence the function of the ion channel, but a similar role for the M4 domain has not been reported. We have identified a methionine residue (Met(823)) in the M4 domain of the NR2A subunit that regulates desensitization and ion channel gating. A tryptophan substitution at this site did not alter the EC(50) for glycine or the peak NMDA EC(50) but decreased the steady-state NMDA EC(50) and markedly increased apparent desensitization, mean open time, and peak current density. Results of rapid solution exchange experiments revealed that changes in microscopic desensitization rates and closing rates could account for the changes in macroscopic desensitization, steady-state NMDA EC(50), and current density. Other amino acid substitutions at this site could increase or decrease the rate of desensitization and mean open time of the ion channel. Both mean open time and desensitization were dependent primarily upon the hydrophobic character of the amino acid at the position. These results demonstrate an important role for hydrophobic interactions at Met(823) in regulation of NMDA receptor function.     

Lactoferrin stimulates A Staphylococcus aureus killing activity of bovine phagocytes in the mammary gland

Lactoferrin (Lf) may play a key role in the clearance of microorganisms from a host. To study in vitro the bactericidal mechanisms of Lf during nonlactating periods, we investigated whether the effects of Lf were influenced by bovine mammary gland secretory cells (MGSC) and fresh normal bovine serum (NBS) as a source of complement. Phagocytic killing tests demonstrated that a phagocytic mixture of unopsonized Staphylococcus aureus (S. aureus) and MGSC in the presence of Lf reduced bacterial growth, compared with that of unopsonized S. aureus and MGSC without Lf. The opsonization with Lf and fresh NBS together resulted in more than a 95% reduction in CFU. The activation of complement induced by Lf also resulted in increased deposition of C3 on S. aureus, and the phagocytic activity of MGSC was augmented by opsonization with Lf and fresh NBS. Inhibition of C3 deposition by Lf was not induced in the presence of Mg-EGTA, but was induced by the addition of bovine Lf antiserum. These results strongly suggest that Lf induces the activation of complement in fresh NBS mainly through an alternative pathway. The results demonstrated a Lf-dependent, antibody-independent and complement-mediated phagocytic killing of S. aureus, and implied that Lf was synergistically capable of activating both the alternative pathway of the bovine complement cascade and phagocytosis by phagocytes.     

Diversity,abundance, and activity of archaeal populations in oil-contaminated groundwater accumulated at the bottom of an underground crude oil storage cavity

Fluorescence in situ hybridization has shown that cells labeled with an Archaea-specific probe (ARCH915) accounted for approximately 10% of the total cell count in oil-contaminated groundwater accumulated at the bottom of an underground crude oil storage cavity. Although chemical analyses have revealed vigorous consumption of nitrate in cavity groundwater, the present study found that the methane production rate was higher than the nitrate consumption rate. To characterize the likely archaeal populations responsible for methane production in this system, fragments of 16S ribosomal DNA (rDNA) were amplified by PCR using eight different combinations of universal and Archaea-specific primers. Sequence analysis of 324 clones produced 23 different archaeal sequence types, all of which were affiliated with the kingdom EURYARCHAEOTA: Among them, five sequence types (KuA1, KuA6, KuA12, KuA16, and KuA22) were obtained in abundance. KuA1 and KuA6 were closely related to the known methanogens Methanosaeta concilii (99% identical) and Methanomethylovorans hollandica (98%), respectively. Although no closely related organism was found for KuA12, it could be affiliated with the family METHANOMICROBIACEAE: KuA16 and KuA22 showed substantial homology only to some environmental clones. Both of these branched deeply in the Euryarchaeota, and may represent novel orders. Quantitative competitive PCR showed that KuA12 was the most abundant, accounting for approximately 50% of the total archaeal rDNA copies detected. KuA1 and KuA16 also constituted significant proportions of the total archaeal rDNA copies (7 and 17%, respectively). These results suggest that limited species of novel archaea were enriched in the oil storage cavity. An estimate of specific methane production rates suggests that they were active methanogens.     

Basic fibroblast growth factor evokes a rapid glutamate release through activation of the MAPK pathway in cultured cortical neurons

We examined the possibility that basic fibroblast growth factor (bFGF) is involved in synaptic transmissions. We found that bFGF rapidly induced the release of glutamate and an increase in the intracellular Ca2+ concentration through voltage-dependent Ca2+ channels in cultured cerebral cortical neurons. bFGF also evoked a significant influx of Na+. Tetanustoxin inhibited the bFGF-induced glutamate release, revealing that bFGF triggered exocytosis. The mitogen-activated protein kinase (MAPK) pathway was required for these acute effects of bFGF. We also found that pretreatment with bFGF significantly enhanced high K+-elicited glutamate release also in a MAPK activation-dependent manner. Therefore, we propose that bFGF exerts promoting effects on excitatory neuronal transmission via activation of the MAPK pathway.     

Identification of a 22-kDa protein required for the degradation of Selenomonas ruminantium lysine decarboxylase by ATP-dependent protease

In Selenomonas ruminantium, a strictly anaerobic, Gram-negative bacterium isolated from sheep rumen, a rapid degradation of lysine decarboxylase (LDC) occurred on entry into the stationary phase of cell growth. Here, we identified a 22-kDa protein as a stimulating factor for the degradation of LDC, which was catalyzed by ATP-dependent protease(s) in S. ruminantium. The purified 22-kDa protein preparation itself had no degradation activity towards LDC but it was required for the degradation of LDC by ATP-dependent proteases in a cell-free system. The 22-kDa protein had similar biochemical and biophysical characteristics to those of antizyme, the regulator for the degradation of mammalian ODC, which had been reported only in mammalian cells. From the sequencing data of the N-terminal 30 amino acid residues of the 22-kDa protein preparation, 22-kDa protein was found to be a new protein which was distinguished from antizyme. This is the first report of the presence of an antizyme-like regulator protein in a prokaryote.     

Role of the second immunoglobulin-like loop of nectin in cell-cell adhesion

We investigated whether and how rat liver thioredoxin reductase spares alpha-tocopherol in biomembranes. Purified hydroperoxides of beta-linoleoyl-gamma-palmitoylphosphatidylcholine were decreased 35% by treatment with thioredoxin reductase and 54% by thioredoxin reductase plus E. coli thioredoxin. Thioredoxin reductase also halved the amount of hydroperoxides that had been formed during photoperoxidation of liposomes composed of beta-linoleoyl-gamma-palmitoylphosphatidylcholine, and of emulsions of both cholesterol and cholesteryl linolenate. In erythrocyte ghosts, thioredoxin reductase spared alpha-tocopherol from oxidation by both soybean lipoxygenase and ferricyanide. Thioredoxin reductase also decreased F(2)-isoprostanes in ghosts oxidized by ferricyanide, suggesting that its ability to spare alpha-tocopherol relates to reduction of lipid hydroperoxides.     

CD27 and CD40 inhibit p53-independent mitochondrial pathways in apoptosis of B cells induced by B cell receptor ligation

B cells in the germinal center are known to undergo apoptosis after B cell receptor (BCR) ligation, a process relevant to immunological tolerance. Human CD27 is a B cell co-stimulatory molecule. The aim of this study was to compare the effects of CD27 and CD40 signals on BCR-mediated apoptosis of B cells. BCR ligation activated mitochondrial apoptotic pathways including down-regulation of Bcl-X(L), dissipation of mitochondrial transmembrane potential, release of cytochrome c, and activation of caspase-9. Each of these effects was significantly inhibited by CD27 and CD40. Bik expression was weakly but significantly down-regulated by CD27 but up-regulated by CD40. BCR ligation resulted in p53 activation including its phosphorylation at Ser(15), nuclear translocation, and target gene p53AIP1 induction. CD27 and CD40 clearly suppressed these processes. Analyses that used dominant-negative p53 variants revealed a low but still substantial level of BCR-mediated apoptosis and intact mitochondria-mediated apoptotic pathway. These pathways were further inhibited by CD27 and CD40, although the cells showed no p53 phosphorylation or p53AIP1 expression. Our results suggested that, at the mitochondrial level, CD27 and CD40 co-stimulatory signals regulated the p53-amplified apoptotic pathway in B cells through the inhibition of p53-independent apoptotic pathway primarily induced by BCR ligation.     

Estrogen enhances depolarization-induced glutamate release through activation of phosphatidylinositol 3-kinase and mitogen-activated protein kinase in cultured hippocampal neurons

Changes in synaptic efficacy are considered necessary for learning and memory. Recently, it has been suggested that estrogen controls synaptic function in the central nervous system. However, it is unclear how estrogen regulates synaptic function in central nervous system neurons. We found that estrogen potentiated presynaptic function in cultured hippocampal neurons. Chronic treatment with estradiol (1 or 10 nm) for 24 h significantly increased a high potassium-induced glutamate release. The estrogen-potentiated glutamate release required the activation of both phosphatidylinositol 3-kinase and MAPK.The high potassium-evoked release with or without estradiol pretreatment was blocked by tetanus neurotoxin, which is an inhibitor of exocytosis. In addition, the reduction in intensity of FM1-43 fluorescence, which labeled presynaptic vesicles, was enhanced by estradiol, suggesting that estradiol potentiated the exocytotic mechanism. Furthermore, protein levels of synaptophysin, syntaxin, and synaptotagmin (synaptic proteins, respectively) were up-regulated by estradiol. We confirmed that the up-regulation of synaptophysin was blocked by the MAPK pathway inhibitor, U0126. These results suggested that estrogen enhanced presynaptic function through the up-regulated exocytotic system. In this study, we propose that estrogen reinforced excitatory synaptic transmission via potentiated-glutamate release from presynaptic sites.