Candida thermophila sp. nov., a novel thermophilic yeast isolated from soil

Yeast strain Y94T, which is capable of growth at high temperature, was isolated from soil in Korea. Characteristics of the strain include asexual reproduction by multilateral budding, the absence of extracellular starch-like compounds, a negative Diazonium blue B colour reaction, and the absence of arthrospores, ballistoconidia and ascospores; the strain can therefore be placed in the genus Candida. A maximum growth temperature of 50-51 degrees C, along with certain other physiological characteristics, and a unique 26S rDNA partial sequence separate this strain from other ascomycetous yeasts. Taken together, these results suggest that the strain is a novel species and the name Candida thermophila sp. nov. (type strain is Y94T = JCM 10994T = KCCM 50661T) is proposed.

Self-assembly of influenza hemagglutinin: studies of ectodomain aggregation by in situ atomic force microscopy

We have used in situ tapping mode atomic force microscopy (AFM) to study the structural morphology of two fragments of the influenza hemagglutinin protein bound to supported bilayers. The two proteins that we studied are the bromelain-cleaved hemagglutinin (BHA), corresponding to the full ectodomain of the hemagglutinin protein, and FHA2, the 127 amino acid N-terminal fragment of the HA2 subunit of the hemagglutinin protein. While BHA is water soluble at neutral pH and is known to bind to membranes via specific interactions with a viral receptor, FHA2 can only be solubilized in water with an appropriate detergent. Furthermore, FHA2 is known to readily bind to membranes at neutral pH in the absence of a receptor. Our in situ AFM studies demonstrated that, when bound to supported bilayers at neutral pH, both these proteins are self-assembled as single trimeric molecules. In situ acidification resulted in further lateral association of the FHA2 without a large perturbation of the bilayer. In contrast, BHA remained largely unaffected by acidification, except in areas of exposed mica where it is aggregated. Remarkably, these results are consistent with previous observations that FHA2 promotes membrane fusion while BHA only induces liposome leakage at low pH. The results presented here are the first example of in situ imaging of the ectodomain of a viral envelope protein allowing characterization of the real-time self-assembly of a membrane fusion protein.

LMP1-induced downregulation of CD99 molecules in Hodgkin and Reed-Sternberg cells

Hodgkin's and Reed-Sternberg (H-RS) cells are morphological hallmarks of Hodgkin's disease (HD). So far, several characteristics frequently seen in H-RS cells from different origins have been described, such as the high expression of Epstein-Barr virus latent membrane protein 1 (LMP1), the elevation of NF-kappaB activity, and the aberrant expression of molecules such as CD15, CD30, and CD99. Despite extensive studies on the nature of H-RS cells, the molecular mechanism by which H-RS cells are generated remained elusive. Recently, the forced down-regulation of CD99 was reported to induce typical H-RS phenotypes in vitro in a B cell line. Furthermore, it was revealed that LMP1 markedly reduces the CD99 expression at the transcriptional level. Since the presence of LMP1 is known to be associated with the H-RS cell formation, the data provide a possibility of linkage between LMP1 and HD via CD99, thus suggesting that, at least in part, the loss of CD99 may play a critical role in the pathogenic sequence to the formation of H-RS cells in HD. In this review, the role of CD99 in the generation of H-RS cells and its molecular mechanism will be suggested.

The 1-127 HA2 construct of influenza virus hemagglutinin induces cell-cell hemifusion

Conformational changes in the HA2 subunit of influenza hemagglutinin (HA) are coupled to membrane fusion. We investigated the fusogenic activity of the polypeptide FHA2 representing 127 amino-terminal residues of the ectodomain of HA2. While the conformation of FHA2 both at neutral and at low pH is nearly identical to the final low-pH conformation of HA2, FHA2 still induces lipid mixing between liposomes in a low-pH-dependent manner. Here, we found that FHA2 induces lipid mixing between bound cells, indicating that the "spring-loaded" energy is not required for FHA2-mediated membrane merger. Although, unlike HA, FHA2 did not form an expanding fusion pore, both acidic pH and membrane concentrations of FHA2, required for lipid mixing, have been close to those required for HA-mediated fusion. Similar to what is observed for HA, FHA2-induced lipid mixing was reversibly blocked by lysophosphatidylcholine and low temperature, 4 degrees C. The same genetic modification of the fusion peptide inhibits both HA- and FHA2-fusogenic activities. The kink region of FHA2, critical for FHA2-mediated lipid mixing, was exposed in the low-pH conformation of the whole HA prior to fusion. The ability of FHA2 to mediate lipid mixing very similar to HA-mediated lipid mixing is consistent with the hypothesis that hemifusion requires just a portion of the energy released in the conformational change of HA at acidic pH.

Sphingomonas aquatilis sp. nov., Sphingomonas koreensis sp. nov., and Sphingomonas taejonensis sp. nov., yellow-pigmented bacteria isolated from natural mineral water

The taxonomic status of four strains from several mineral water sources in Taejon, Korea, was examined. The DNA base compositions of these strains ranged from 62 to 66 mol %. All of the strains contained sphingolipids and ubiquinone 10 as the main respiratory quinone. The cellular fatty acids of these strains included octadecenoic acid, hexadecanoic acid and 2-hydroxymyristic acid, without 3-hydroxy fatty acids. On the basis of morphological, physiological and chemotaxonomic characteristics, together with 16S rDNA sequence comparison and DNA-DNA reassociation data, three new species of the genus Sphingomonas are proposed for the strains isolated from natural mineral water: Sphingomonas aquatilis sp. nov. for strain JSS7T (= KCTC 2881T = KCCM 41067T), Sphingomonas koreensis sp. nov. for strains JSS26T (= KCTC 2882T = KCCM 41069T) and JSS28 (= KCTC 2883 = KCCM 41066) and Sphingomonas taejonensis sp. nov. for strain JSS54T (= KCTC 2884T = KCCM 41068T).

The neuronal t-SNARE complex is a parallel four-helix bundle

Assembly of the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complex is an essential step for neurotransmitter release in synapses. The presynaptic plasma membrane associated proteins (t-SNAREs), SNAP-25 (synaptosome-associated protein of 25,000 Da) and syntaxin 1A may form an intermediate complex that later binds to vesicle-associated membrane protein 2 (VAMP2). Using spin labeling electron paramagnetic resonance (EPR), we found that the two t-SNARE proteins assemble into a parallel four-helix bundle that consists of two identical syntaxin 1A components and the N-terminal and C-terminal domains of SNAP-25. Although the structure is generally similar to that of the final SNARE complex, the middle region of the helical bundle appears more flexible in the t-SNARE complex. Such flexibility might facilitate interactions between VAMP2 and the t-SNARE complex.

Fungicidal effect of antimicrobial peptide, PMAP-23, isolated from porcine myeloid against Candida albicans

The antifungal activity and mechanism of a 23-mer peptide, PMAP-23, derived from pig myeloid was investigated. PMAP-23 displayed strong antifungal activity against yeast and mold. To investigate the antifungal mechanism of PMAP-23, fluorescence activated flow cytometry and confocal laser scanning microscopy were performed. Candida albicans treated with PMAP-23 showed higher fluorescence intensity by propidium iodide(PI) staining, which was similar to that of Melittin than untreated cells. Confocal microscopy showed that the peptide was located in the plasma membrane. The action of peptides against fungal cell membranes was examined by treating prepared protoplasts of C. albicans with the peptide and lipid vesicle titration test. The result showed that the peptide prevented the regeneration of fungal cell walls and induced release of the fluorescent dye trapped in the artificial membrane vesicles, indicating that the peptide exerts its antifungal activity by acting on the plasma lipid membrane.

Frequency of acyclovir-resistant herpes simplex virus in clinical specimens and laboratory isolates

The proportion of acyclovir (ACV)-resistant herpes simplex virus (HSV) isolates in clinical specimens and laboratory isolates was determined. HSV isolates in clinical specimens and laboratory isolates were cultured in the absence or presence of 5 microg of ACV per ml. The frequency of ACV-resistant HSV was calculated as (average virus titer in the wells with ACV)/(average virus titer in the wells without ACV). The mutation frequency of HSV type 1 isolates in clinical samples (directly from patient lesions) was 7.5 x 10(-4) +/- 2.5 x 10(-4) (mean +/- standard error), and that of HSV type 2 isolates was 15.0 x 10(-4) +/- 4.6 x 10(-4). The mutation frequencies of isolates derived in the laboratory from these clinical samples were very similar. Similarly, the 50% inhibitory concentrations for isolates in clinical samples and laboratory isolates were identical. The frequencies of ACV-resistant HSV types 1 and 2 were in a narrow range of 7.5 x 10(-4) to 15.0 x 10(-4) among isolates in clinical specimens and did not change for laboratory-derived pools of viral isolates.

CD99 regulates the transport of MHC class I molecules from the Golgi complex to the cell surface

The down-regulation of surface expression of MHC class I molecules has recently been reported in the CD99-deficient lymphoblastoid B cell line displaying the characteristics of Hodgkin's and Reed-Sternberg phenotype. Here, we demonstrate that the reduction of MHC class I molecules on the cell surface is primarily due to a defect in the transport from the Golgi complex to the plasma membrane. Loss of CD99 did not affect the steady-state expression levels of mRNA and protein of MHC class I molecules. In addition, the assembly of MHC class I molecules and the transport from the endoplasmic reticulum to the cis-Golgi occurred normally in the CD99-deficient cells, and no difference was detected between the CD99-deficient and the control cells in the pattern and degree of endocytosis. Instead, the CD99-deficient cells displayed the delayed transport of newly synthesized MHC class I molecules to the plasma membrane, thus causing accumulation of the molecules within the cells. The accumulated MHC class I molecules in the CD99-deficient cells were colocalized with alpha-mannosidase II and gamma-adaptin in the Golgi compartment. These results suggest that CD99 may be associated with the post-Golgi trafficking machinery by regulating the transport to the plasma membrane rather than the endocytosis of surface MHC class I molecules, providing a novel mechanism of MHC class I down-regulation for immune escape.

Arachidonic acid and nonsteroidal anti-inflammatory drugs induce conformational changes in the human prostaglandin endoperoxide H2 synthase-2 (cyclooxygenase-2)

By using the technique of site-directed spin labeling combined with EPR spectroscopy, we have observed that binding of arachidonic acid and nonsteroidal anti-inflammatory drugs induces conformational changes in the human prostaglandin endoperoxide H(2) synthase enzyme (PGHS-2). Line shape broadening resulting from spin-spin coupling of nitroxide pairs introduced into the membrane-binding helices of PGHS-2 was used to calculate the inter-helical distances and changes in these distances that occur in response to binding various ligands. The inter-residue distances determined for the PGHS-2 holoenzyme using EPR were 1-7.9 A shorter than those of the crystal structure of the PGHS-2 holoenzyme. However, inter-helical distances calculated and determined by EPR for PGHS-2 complexed with arachidonic acid, flurbiprofen, and SC-58125 were in close agreement with those obtained from the cognate crystal structures. These results indicate that the structure of the solubilized PGHS-2 holoenzyme measured in solution differs from the crystal structure of PGHS-2 holoenzyme obtained by x-ray analysis. Furthermore, binding of ligands induces a conformational change in the holo-PGHS-2, converting it to a structure similar to those obtained by x-ray analysis. Proteolysis protection assays had previously provided circumstantial evidence that binding of heme and non-steroidal anti-inflammatory drugs alters the conformation of PGHS, but the present experiments are the first to directly measure such changes. The finding that arachidonate can also induce a conformational change in PGHS-2 was unexpected, and the magnitude of changes suggests this structural flexibility may be integral to the cyclooxygenase catalytic mechanism.

Light-induced rotation of a transmembrane alpha-helix in bacteriorhodopsin

Spin labeling EPR spectroscopy has been used to characterize light-induced conformational changes of bacteriorhodopsin (bR). Pairs of nitroxide spin labels were attached to engineered cysteine residues at strategic positions near the cytoplasmic ends of transmembrane alpha-helices B, F, and G in order to monitor distance changes upon light activation. The EPR analysis of six doubly labeled bR mutants indicates that the cytoplasmic end of helix F not only tilts outwards, but also rotates counter-clockwise during the photocycle. The direction of the rotation of helix F is the opposite of the clockwise rotation previously reported for bovine rhodopsin. The opposite chirality of the F helix rotation in the two systems is perhaps related to the differences in the cis-trans photoisomerization of the retinal in the two proteins. Using time-resolved EPR, we monitored the rotation of helix F also in real time, and found that the signal from the rotation arises concurrently with the reprotonation of the retinal Schiff base.

Insights into a structure-based mechanism of viral membrane fusion

A number of different viral spike proteins, responsible for membrane fusion, show striking similarities in their core structures. The prospect of developing a general structure-based mechanism seems plausible in light of these newly determined structures. Influenza hemagglutinin (HA) is the best-studied fusion machine, whose action has previously been described by a hypothetical "spring-loaded" model. This model has recently been extended to explain the mechanism of other systems, such as HIV gp120-gp41. However, evidence supporting this idea is insufficient, requiring re-examination of the mechanism of HA-induced membrane fusion. Recent experiments with a shortened construct of HA, which is able to induce lipid mixing, have provided evidence for an alternative scenario for HA-induced membrane fusion and perhaps that of other viral systems.

Block of sodium currents in rat dorsal root ganglion neurons by diphenhydramine

To elucidate the local anesthetic mechanism of diphenhydramine, its effects on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) sodium currents in rat dorsal root ganglion (DRG) neurons were examined by the whole-cell voltage clamp method. Diphenhydramine blocked TTX-S and TTX-R sodium currents with K(d) values of 48 and 86 microM, respectively, at a holding potential of -80 mV. It shifted the conductance-voltage curve for TTX-S sodium currents in the depolarizing direction but had little effect on that for TTX-R sodium currents. Diphenhydramine caused a shift of the steady-state inactivation curve for both types of sodium currents in the hyperpolarizing direction. The time-dependent inactivation became faster and the recovery from the inactivation was slowed by diphenhydramine in both types of sodium currents. Diphenhydramine produced a profound use-dependent block when the cells were repeatedly stimulated with high-frequency depolarizing pulses. The use-dependent block was more pronounced in TTX-R sodium currents. The results show that diphenhydramine blocks sodium channels of sensory neurons similarly to local anesthetics.

Protective effect of boldine on oxidative mitochondrial damage in streptozotocin-induced diabetic rats

Increased oxidative stress has been suggested to be involved in the pathogenesis and progression of diabetic tissue damage. Several antioxidants have been described as beneficial for oxidative stress-associated diseases. Boldine ([s]-2,9-dihydroxy-1, 10-dimethoxyaporphine) is a major alkaloid found in the leaves and bark of boldo (Peumus boldus Molina), and has been shown to possess antioxidant activity and anti-inflammatory effects. From this point of view, the possible anti-diabetic effect of boldine and its mechanism were evaluated. The experiments were performed on male rats divided into four groups: control, boldine (100 mg kg(-1), daily in drinking water), diabetic [single dose of 80 mg kg(-1)of streptozotocin (STZ), i.p.] and diabetic simultaneously fed with boldine for 8 weeks. Diabetic status was evaluated periodically with changes of plasma glucose levels and body weight in rats. The effect of boldine on the STZ-induced diabetic rats was examined with the formation of malondialdehydes and carbonyls and the activities of endogenous antioxidant enzymes (superoxide dismutase and glutathione peroxidase) in mitochondria of the pancreas, kidney and liver. The scavenging action of boldine on oxygen free radicals and the effect on mitochondrial free-radical production were also investigated. The treatment of boldine attenuated the development of hyperglycemia and weight loss induced by STZ injection in rats. The levels of malondialdehyde (MDA) and carbonyls in liver, kidney and pancreas mitochondria were significantly increased in STZ-treated rats and decreased after boldine administration. The activities of mitochondrial manganese superoxide dismutase (MnSOD) in the liver, pancreas and kidney were significantly elevated in STZ-treated rats. Boldine administration decreased STZ-induced elevation of MnSOD activity in kidney and pancreas mitochondria, but not in liver mitochondria. In the STZ-treated group, glutathione peroxidase activities decreased in liver mitochondria, and were elevated in pancreas and kidney mitochondria. The boldine treatment restored the altered enzyme activities in the liver and pancreas, but not the kidney. Boldine attenuated both STZ- and iron plus ascorbate-induced MDA and carbonyl formation and thiol oxidation in the pancreas homogenates. Boldine decomposed superoxide anions, hydrogen peroxides and hydroxyl radicals in a dose-dependent manner. The alkaloid significantly attenuated the production of superoxide anions, hydrogen peroxide and nitric oxide caused by liver mitochondria. The results indicate that boldine may exert an inhibitory effect on STZ-induced oxidative tissue damage and altered antioxidant enzyme activity by the decomposition of reactive oxygen species and inhibition of nitric oxide production and by the reduction of the peroxidation-induced product formation. Boldine may attenuate the development of STZ-induced diabetes in rats and interfere with the role of oxidative stress, one of the pathogeneses of diabetes mellitus.

DNA-DNA relatedness among Thermoactinomyces species: Thermoactinomyces candidus as a synonym of Thermoactinomyces vulgaris and Thermoactinomyces thalpophilus as a synonym of Thermoactinomyces sacchari

DNA-DNA relatedness of all validly described Thermoactinomyces species was determined to infer the genetic relationships between them. The levels of DNA-DNA relatedness among the type strains of Thermoactinomyces species ranged from 2-5 to 92.8%. Based on DNA relatedness data, the type strains of Thermoactinomyces intermedius, Thermoactinomyces putidus, Thermoactinomyces dichotomicus and Thermoactinomyces peptonophilus were considered to be distinct species of the genus Thermoactinomyces. However, the relationship between the type strains of Thermoactinomyces vulgaris and Thermoactinomyces candidus and the relationship between the type strains of Thermoactinomyces sacchari and Thermoactinomyces thalpophilus were reevaluated from levels of DNA-DNA relatedness. The independent DNA relatedness values between Thermoactinomyces vulgaris KCTC 9076T and Thermoactinomyces candidus KCTC 9557T were 90.8 and 92.8%. Thermoactinomyces thalpophilus KCTC 9789T and Thermoactinomyces sacchari KCTC 9790T exhibited independent values of 85.6 and 87.3%. Accordingly, on the basis of DNA-DNA relatedness data together with 16S rDNA sequence data determined recently, it is proposed that Thermoactinomyces candidus should be considered as a synonym of Thermoactinomyces vulgaris and Thermoactinomyces thalpophilus be considered as a synonym of Thermoactinomyces sacchari.

Amitriptyline modulation of Na(+) channels in rat dorsal root ganglion neurons

The effects of amitriptyline, a tricyclic antidepressant, on tetrodotoxin-sensitive and tetrodotoxin-resistant Na(+) currents in rat dorsal root ganglion neurons were studied using the whole-cell patch clamp method. Amitriptyline blocked both types of Na(+)currents in a dose-and holding potential-dependent manner. At the holding potential of -80 mV, the apparent dissociation constants (K(d)) for amitriptyline to block tetrodotoxin-sensitive and tetrodotoxin-resistant Na(+) channels were 4.7 and 105 microM, respectively. These values increased to 181 and 193 microM, respectively, when the membrane was held at a potential negative enough to remove the steady-state inactivation. Amitriptyline dose-dependently shifted the steady-state inactivation curves in the hyperpolarizing direction and increased the values of the slope factors for both types of Na(+) channels. The voltage dependence of the activation of both types of Na(+) channels was shifted in the depolarizing direction. It was concluded that amitriptyline blocked the two types of Na(+) channels in rat sensory neurons by modulating the activation and the inactivation kinetics.

Phylogenetic analysis of the small hydrophobic (SH) gene of mumps virus in Korea: identification of a new genotype

Viral RNAs extracted from fifteen mumps virus isolated from throat swab, saliva, blood, urine or CSF during mumps epidemics between 1997-1998 in Korea were amplified by reverse transcriptase-polymerase chain reaction (RT-PCR) and compared by nucleotide sequencing of the small hydrophobic (SH) gene. The deduced amino acid sequences of the SH gene were aligned with the published sequences of mumps virus isolated in different geographic areas. A comparison of the SH gene of mumps viruses in Korea indicated 96.2-100% and 91.2-100% similarity at the nucleotide and amino acid levels, respectively. Phylogenetic analysis, using the neighbor-joining method, showed that Korean mumps virus strains formed a genetically distinct monophyletic group from previously reported genotypes based on the 315-bp length nucleotide and 57 deduced amino acid sequences of the SH gene, and possibly be designated as a new genotype (I).

ATP evokes different currents in TTX-sensitive and TTX-resistant cells of dorsal root ganglia

The relationship between the level of expression of tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) sodium currents and the occurrence of two kinetically different ATP-induced currents in rat dorsal root ganglion neurons was studied. ATP evoked two distinct types of currents, one with fast activation and desensitization (I-fast) and the other with slow and persistent development (I-slow). In all TTX-S cells which expressed solely TTX-S sodium currents ATP evoked I-fast. The other cells expressed a variable proportion of TTX-S and TTX-R sodium currents. Only 15% of these TTX-R+S cells responded to ATP with I-fast. I-slow was evoked in both cell types but the magnitude of response was much greater in TTX-R+S cells. This result suggests that a different array of ion channels is equipped in different types of sensory neurons.

Inhibitory action of thimerosal, a sulfhydryl oxidant, on sodium channels in rat sensory neurons

The effects of thimerosal, a sulfhydryl oxidizing agent, on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) sodium channels in rat dorsal root ganglion neurons were studied using the whole-cell patch clamp technique. Thimerosal blocked the two types of sodium channels in a dose-dependent manner. The inhibitory effect of thimerosal was much more pronounced in TTX-R sodium channels than TTX-S sodium channels. The effect of thimerosal was irreversible upon wash-out with thimerosal-free external solution. However, dithiothreitol, a reducing agent, partially reversed it. Thimerosal shifted the steady-state inactivation curves for both types of sodium channels in the hyperpolarizing direction. The voltage dependence of activation of both types of sodium channels was shifted in the depolarizing direction by thimerosal. The inactivation rate in both types of sodium channels increased after thimerosal treatment. All these effects of thimerosal would add up to cause a depression of sodium channel function leading to a diminished neuronal excitability.

Gordonia nitida sp. nov., a bacterium that degrades 3-ethylpyridine and 3-methylpyridine

A bacterial strain, LE31T, which is capable of degrading 3-ethylpyridine and 3-methylpyridine, was isolated from an industrial wastewater and was taxonomically studied by using a polyphasic approach. Strain LE31T was identified as a member of the genus Gordonia on the basis of chemotaxonomic characteristics and phylogenetic inference-based 16S rDNA sequence. The cell wall contained meso-diaminopimelic acid, arabinose and galactose (wall chemotype IV). The predominant menaquinone was MK-9(H2). The mycolic acids contained 47-55 carbon atoms. The major fatty acids were C16:0, C18:1 omega9c, 10-methyl-C18:0 (TBSA). The G+C content of DNA was 67 mol%. The 16S rDNA sequence of strain LE31T was most similar to that of the type strain of Gordonia rubropertincta. The differences in some phenotypic characteristics and the genetic distinctiveness distinguish strain LE31T from the Gordonia species described previously. Therefore it is proposed that strain LE31T should be placed in the genus Gordonia as a new species. The name Gordonia nitida is proposed for strain LE31T. The type strain of the new species is strain LE31T (= KCTC 0605BPT = KCCM 80004T).

Factors determining vesicular lipid mixing induced by shortened constructs of influenza hemagglutinin

The HA2 subunit of influenza hemagglutinin is responsible for fusion of the viral and host-cell membranes during infection. An N-terminal 127 amino acid construct of HA2, FHA2-127, is shown to induce lipid mixing of large unilamellar vesicles under endosomal low pH conditions. Thus, FHA2 could serve as a good model system for biophysical studies of membrane fusion. With FHA2, we began to develop a mechanistic model which could explain how this short construct facilitates membrane fusion. In this endeavor, we studied the possible role of the kinked loop region (amino acids 105-113). A construct missing this loop, FHA2-90, although able to induce lipid mixing, has lost the sharp pH-dependent transition seen with FHA2-127 and native HA. In addition, FHA2-127 promotes extensive vesicle aggregation more effectively than FHA2-90 upon acidification. These data suggest that the kinked loop may play a pH-dependent regulatory role. To test this, we compared bis-ANS binding to the two constructs and observed that binding to FHA2-127 increases at a faster rate than FHA2-90 as the pH is decreased, indicating that the kinked loop not only is an ANS-binding site, but that it binds better at low pH. The pH dependence of this transition directly correlates with that observed in lipid mixing. Further, cysteine mutations of acidic residues in the kinked region are both fusion inactive and bind much less ANS, whereas a similar mutation of a threonine residue had little effect on fusion activity or ANS binding. This evidence lends further support to our idea that the kinked loop serves a regulatory role. To test the physiological relevance of the FHA2-127 fusion mechanism, we studied the effects of a G1E mutation, known to abolish fusion in native HA. We found that G1E-127 is fusion inactive as expected. This evidence indirectly suggests that the mechanism of FHA2-127 is perhaps physiologically relevant and from its study, we can learn much about the mechanism of native HA.

N-Ethylmaleimide modulation of tetrodotoxin-sensitive and tetrodotoxin-resistant sodium channels in rat dorsal root ganglion neurons

The effects of N-ethylmaleimide (NEM), an alkylating reagent to protein sulfhydryl groups, on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) sodium channels in rat dorsal root ganglion (DRG) neurons were studied using the whole cell configuration of patch-clamp technique. When currents were evoked by step depolarizations to 0 mV from a holding potential of -80 mV NEM decreased the amplitude of TTX-S sodium current, but exerted little or no effect on that of TTX-R sodium current. The inhibitory effect of NEM on TTX-S sodium channel was mainly due to the shift of the steady-state inactivation curve in the hyperpolarizing direction. NEM did not affect the voltage-dependence of the activation of TTX-S sodium channel. The steady-state inactivation curve for TTX-R sodium channel was shifted by NEM in the hyperpolarizing direction as that for TTX-S sodium channel. NEM caused a change in the voltage-dependence of the activation of TTX-R sodium channel unlike TTX-S sodium channel. After NEM treatment, the amplitudes of TTX-R sodium currents at test voltages below -10 mV were increased, but those at more positive voltages were not affected. This was explained by the shift in the conductance-voltage curve for TTX-R sodium channels in the hyperpolarizing direction after NEM treatment.

Viral latent membrane protein 1 (LMP-1)-induced CD99 down-regulation in B cells leads to the generation of cells with Hodgkin's and Reed-Sternberg phenotype

Recently we reported that the down-regulation of CD99 (Mic2) is a primary requirement for the generation of Hodgkin's and Reed-Sternberg (H-RS) cells seen in Hodgkin's disease. In this study, we provide evidence that the down-regulation of CD99 is induced by high expression of Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1), which is highly expressed in H-RS cells of EBV-associated Hodgkin's disease. To investigate the effect of LMP-1 on the expression of CD99 in vitro, we established a stable cell line by transfecting an SV40-early promoter driven-LMP-1 expression construct into a neoplastic lymphoblastoid B cell line, IM9, in which the level of endogenous LMP-1 expression is almost negligible. In this cell line, the overexpression of LMP-1 led to the down-regulation of CD99 and the acquisition of morphological and functional characteristics of H-RS cells indistinguishable from those in lymph nodes of Hodgkin's disease patients and in CD99-deficient B cells. In addition, induced LMP-1 expression in an EBV-negative B cell clone, BJAB, directly caused the down-regulation of surface CD99 expression. Northern and Western analysis data, showing that overexpression of LMP-1 negatively influenced the expression of CD99, were supported by experiments in which a CD99 promoter-driven luciferase promoter reporter construct transfected into 293T cells was down-regulated when LMP-1 was coexpressed. Therefore, our data strongly suggest that the EBV LMP-1 protein plays a pivotal role in the down-regulation of CD99 via transcriptional regulation, which leads to the generation of the H-RS cells. (Blood. 2000;95:294-300)

High CD99 expression in memory T and B cells in reactive lymph nodes

We investigated the expression of CD99 in 35 hyperplastic perigastric lymph nodes, which were resected for gastric carcinoma or chronic peptic ulcer. Essentially, all lymphocytes in lymph nodes expressed CD99, but there were two populations with respect to the intensity of CD99 expression--CD99high and CD99low cells. We showed CD99high cells were distributed in paracortical and medullary cords by immunohistochemical study while germinal center cells were CD99low. Using three-color flow cytometric analysis with CD3, CD4, CD8, CD19, CD23, CD45RA, CD45RO, CD69, CD138, IgM, IgD, and IgG, most of CD99high cells were shown to be activated/memory T cells. CD4+CD45RO+ T cells were the subset revealing the highest intensity of CD99 expression while CD4+CD45RA+ T cells were CD99low. Among B cells, IgG+ B cells revealed a higher level of CD99 molecules than IgM+ B cells. These results suggest that CD99 is one of activation-related molecules which are upregulated in recently activated lymphocytes.

A piston model for transmembrane signaling of the aspartate receptor

To characterize the mechanism by which receptors propagate conformational changes across membranes, nitroxide spin labels were attached at strategic positions in the bacterial aspartate receptor. By collecting the electron paramagnetic resonance spectra of these labeled receptors in the presence and absence of the ligand aspartate, ligand binding was shown to generate an approximately 1 angstrom intrasubunit piston-type movement of one transmembrane helix downward relative to the other transmembrane helix. The receptor-associated phosphorylation cascade proteins CheA and CheW did not alter the ligand-induced movement. Because the piston movement is very small, the ability of receptors to produce large outcomes in response to stimuli is caused by the ability of the receptor-coupled enzymes to detect small changes in the conformation of the receptor.