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S Lee

Publications and source records attributed to S Lee.

At least 739 records · Page 41Linked to original sources
PubMed1997

Conformations and orientations of aromatic amino acid residues of tachyplesin I in phospholipid membranes.

Tachyplesin I, an antibacterial and antiviral heptadecapeptide from the hemocyte debris of Tachypleus tridentatus, contains four aromatic amino acids (Trp2, Phe4, Tyr8, and Tyr13) which have been shown to be crucial for activity. In order to investigate conformations and orientations of the aromatic amino acid residues of tachyplesin I in lipid bilayers, its analogs, [Phe8]- and/or [Phe13]-tachyplesin(s) I in which Tyr8 and Tyr13 are replaced by Phe, were synthesized. Circular dichroism spectral studies showed that three peptides are considerably different in conformation in aqueous solution at pH 8.0 whereas they take similar conformations in the presence of neutral egg yolk phosphatidylcholine (EYPC) liposomes. Energy transfer kinetics showed that the distances of Trp2-Tyr8 and Trp2-Tyr13 are 16 A (max of 18.3 A, min of 15.1 A) and 18 A (max of 20.2 A, min of 16.6 A) in buffer but are 12 A (max of 15.2 A, min of 8.6 A) and 18 A (max of 22.9 A, min of 12.9 A), respectively, in the presence of acidic EYPC/EYPG (3:1) liposomes. Decay kinetics for Trp2 fluorescence indicated that Trp2 takes at least three conformations in buffer and in acidic liposomes where fractions of three Trp2 conformers vary by changing the medium from buffer to acidic liposomes. Although tachyplesin I is not in amphiphilic structure in buffer in spite of its rigid antiparallel beta-conformation, its interaction with lipid bilayers appears to induce amphiphilic structure via minor alteration of peptide backbone and side chain orientations, resulting in shortening the distance of Trp2-Tyr8.

Amino Acid Sequence↗
PubMed1997

De novo design, synthesis, and characterization of a pore-forming small globular protein and its insertion into lipid bilayers.

The question of how to design a water-soluble globular protein remains. We report here the synthesis of a native-like and pore-forming small globular protein (SGP, 69 amino acid residues). The protein was designed to have four helices: a Trp-containing short hydrophobic helix in the middle surrounded by three Tyr-containing long basic amphiphilic helices. Size-exclusion chromatography and CD measurements indicated that in buffer solution SGP is monomeric with a 50% helical structure. SGP did not completely denature even at high temperature (90 degrees C) and at relatively high Gu x HCl concentration so that the denaturant concentration at the midpoint of the transition is 5 M. Dye binding studies and fluorescence energy transfer experiments showed that SGP possesses a hydrophobic binding site and its Trp of the central helix is present at a relatively hydrophobic region and accepts the energy from Tyr(s) in other amphiphilic helices, indicating that SGP takes a stable globular-like structure in aqueous solution. From the depth-dependent fluorescent studies using egg PC liposomes containing n-doxyl fatty acids and brominated phospholipid as quenchers, it was found that the hydrophobic central alpha-helix is able to enter spontaneously into the lipid bilayers and the Trp in the central alpha-helix is located at about the middle of the alkyl chain in the outer layer of the phospholipid bilayer. The peptide is also able to increase the membrane permeability with two modes of current (basal current and single ion channel) in planar phospholipid bilayers, indicating the spontaneous insertion of the protein into the lipid bilayer (basal current) and then the formation of a uniform size of channel pore (14 pS). SGP is useful as a basic and starting model to find good amino acid sequences that fold to a desired protein structure and to search translocation mechanisms from aqueous solution into lipid bilayers.

Amino Acid Sequence↗
PubMed1997

Inhibition of 5-lipoxygenase blocks IL-1 beta-induced vascular adhesion molecule-1 gene expression in human endothelial cells.

Inflammation is characterized by the recruitment of leukocytes and their subsequent migration from the vasculature into the tissue, where they often cause severe damage. Endothelial cells play a major role in this cascade by expressing cell surface adhesion molecules, such as VCAM-1 and ICAM-1, and chemokines, in response to cytokines. Many of these genes are under the control of inflammatory response transcription factors such as nuclear factor (NF)-kappa B. In this study, we examined the effects of 5-lipoxygenase inhibitors (nordihydroguaiaretic acid and AA861) on IL-1 beta-induced VCAM-1 gene expression in HUVECs. We demonstrated that 5-lipoxygenase inhibitors, but not cyclooxygenase inhibitors, block IL-1 beta-induced VCAM-1 cell surface expression and promoter activity. In transiently transfected HUVECs, NF-kappa B-dependent gene expression was inhibited by 5-lipoxygenase inhibitors. These inhibitors did not block IL-1 beta-induced nuclear translocation of NF-kappa B, inhibitor of kappa B-alpha proteolytic degradation, or significantly reduce phosphorylation of p65. These studies indicate that inhibition of 5-lipoxygenase blocks cytokine-induced VCAM-1 gene expression by reducing the functional activity of NF-kappa B/Rel proteins in HUVECs.

Benzoquinones↗
PubMed1997

The von Hippel-Lindau tumor-suppressor gene product forms a stable complex with human CUL-2, a member of the Cdc53 family of proteins.

The inactivation of the von Hippel-Lindau (VHL) gene predisposes affected individuals to VHL syndrome and is an early genetic event associated with sporadic renal cell carcinoma and CNS hemangioblastomas. The VHL protein (pVHL) has been shown to form a stable complex with elongin B and elongin C, two factors that stabilize and activate the transcription elongation factor elongin A. Here, Hs-CUL-2, a member of the recently identified multigene family, the cullins, is shown to specifically associate with the trimeric pVHL-elongin B-C (VBC) complex in vitro and in vivo. Nearly 70% of naturally occurring cancer-predisposing mutations of VHL disrupt this interaction. The pVHL-Hs-CUL-2 association is strictly dependent on the integrity of the trimeric VBC complex. Immunofluorescence studies show Hs-CUL-2 to be a cytosolic protein that can be translocated to the nucleus by pVHL. Recently it has been shown that a yeast Hs-CUL-2 homolog, Cdc53, is part of a ubiquitin protein ligase complex that targets cell cycle proteins for degradation by the ubiquitin proteolytic pathway. In Caenorhabditis elegans, a null mutation of another Hs-cul-2 homolog, Ce-cul-1, results in hyperplasia in all tissues and is required for cell cycle exit. Hence, Hs-cul-2 may be required for VHL function and, therefore, may be a candidate human tumor-suppressor gene.

Amino Acid Sequence↗
PubMed1997

Micelle Formation of Dodecylammonium Surfactant with Mixed Counterions: Perfluorocarboxylate and Alkanesulfonate Ions

Micelle formation was studied for four mixing combinations of dodecylammonium (DA) salts having perfluorocarboxylate ions (trifluoroacetate (PA) and pentafluoropropionate (PP) and alkane sulfonate ions (methane sulfonate (MS) and ethane sulfonate (ES)) as their counterions, i.e., DAPA/DAMS, DAPA/DAES, DAPP/DAMS, and DAPP/DAES. The fluorocarbon anions as counterions exhibited that the degree of counterion binding to micelle (beta) as well as the extent of stabilizing micelles and lowering ability of critical micellization concentration (CMC) are greater than hydrocarbon anions. The "mixed micelle formation" was examined in terms of CMC as a function of mole fraction (Xi) in each surfactant mixture. The CMCs of the mixed surfactant systems studied here, correspond to those of "surfactant with mixed counterions". However, by regarding tentatively those combinations as binary mixed surfactant systems, the CMC vs Xi curves (singly dispersed phase curves) as well as CMC vs micellar composition (Yi) curves (micellar phase curves) were simulated by applying the present authors' and Rubingh's equations which have been derived respectively with and without taking into account mutual added-salt effect (or the beta value for each pure system). A negative deviation from ideal mixing was observed for each combination, indicating that mixing of fluorocarbon anion with hydrocarbon anion as counterion of DA salts results in more stabilized micelle formation. Plotting the derivative of specific conductance (kappa) by total concentration of surfactant (Ct), dkappa/dCt against Ct, the curves showed a constant value at the sufficiently higher concentration range than CMC, and the constant values were found able to be related to the degree of dissociation of micelles (alpha). Even for the mixed systems, the alpha or beta values were estimated from the conductivity data. The greater power to stabilize micelle formation by fluorocarbon ions was interpreted on the basis of concept of "contact hydrophobic interaction" proposed by Mukerjee (Mukerjee, P., Colloids Surf. A: Physicochem. Eng. Aspects 84, 49 (1994)).

Journal Article↗
PubMed1997

Can energy transfer be an indicator for DNA intercalation?

Contact energy transfer from DNA bases to various ligands, which can be represented by the ratio of the fluorescence intensity Q(lambda)/Q310nm, is measured by conventional fluorometer. 4',6-Diamidino-2-phenylindole and 2'-(4-hydroxyphenyl)-5-(4-methyl-1-piperazinyl)-2,5'-bi-1H-benzimidazole can accept energy from DNA bases and exhibit the ratio Q(lambda)/Q310nm, similar to that of intercalators, although these molecules are known to bind preferentially to the minor groove of the adenine-thymine rich region of DNA. When porphyrin is intercalated in DNA or poly[d(G-C)2], the shape of the ratio Q(lambda)/Q310nm is distinct from that of the ethidium-DNA complex with two maxima at 250 nm and 280 nm. The ratio Q(lambda)/Q310nm of the porphyrin-poly[d(A-T)2] complex, in which porphyrin is known to bind 'outside' of the DNA stem, is similar to that of intercalators. Therefore, energy from excited DNA bases can be transferred not only to an intercalated ligand through direct contact but also to that bound in the minor groove. It follows from this observation that using energy transfer as a criterion for DNA intercalation requires extreme caution.

DNA↗
PubMed1997

Human p53 binds Holliday junctions strongly and facilitates their cleavage.

Holliday junctions in DNA are generated as a product of homologous recombination events. To test the hypothesis that human p53 may bind to Holliday junctions, synthetic junctions with four approximately 75-base pair (Hol75) or approximately 565-base pair (Hol565) arms were generated. As seen by electron microscopy, under conditions in which 50-61% of the Hol565 DNAs were bound by p53, 80-96% of the p53 was located specifically at the junction with, in the latter case, only 4% of the p53 visualized at the DNA ends or along the arms. Given the large number of potential binding sites, this represents very high specificity for the junctions. Gel retardation assays using the Hol75 DNA confirm these observations, and indicate that the tight junction complexes have a half-life of greater than 4 h. The binding of p53 to three-way junctions is severalfold less than to four-way junctions. Addition of p53 greatly increases the rate of resolution of the Hol75 DNA by T4 endonuclease VII and T7 endonuclease I, two enzymes known to cleave such junctions. This latter finding further confirms the interaction of p53 with Holliday junctions and suggests that p53 binding facilitates their resolution in vivo.

Binding Sites↗
PubMed1997

Gene deficiency of glutathione S-transferase mu isoform associated with susceptibility to lung cancer in a Chinese population.

Increased lung cancer risk associated with genetic polymorphism of glutathione S-transferase (GST, EC 2.5.1.18) isozyme mu was examined in a Chinese population. A significantly higher proportion in lung cancer patients showed GST mu deficiency compared with control group (71.0% vs. 51.1%, P < 0.005). Although the susceptibility to lung cancer showing gene deletion for GST mu isoform in non-smoking group is not significantly different from that in smoking group, a great number of individuals with gene deletion was found among cancer patients who are less than 50 years old. The pathology of lung tumors related to that lack of class mu isoform which occurred most frequently in patients with small cell carcinomas. Thus, present data further support that sensitivity to chemical toxins and pulmonary carcinogens may be affected by GST mu isoform polymorphism.

Adenocarcinoma↗
PubMed1997

Saccharomyces cerevisiae MSH2, a mispaired base recognition protein, also recognizes Holliday junctions in DNA.

Genetic and biochemical studies have suggested that mismatch repair proteins interact with recombination intermediates to prevent recombination, or to limit the extent of formation of heteroduplex DNA during recombination between divergent DNA sequences. To test the idea that mismatch repair proteins regulate recombination by interacting with recombination intermediates, we investigated whether the Saccharomyces cerevisiae MutS homolog MSH2 could interact with Holliday junctions. Both filter-binding and electron-microscopic analysis showed that MSH2 bound to duplex DNA molecules containing Holliday junctions with a higher affinity than to control duplex DNA, single-stranded DNA or a control duplex DNA containing a mispaired base. The MSH2-Holliday junction complexes were also more stable than MSH2-duplex DNA complexes. This observation suggests that MSH2 protein could directly coordinate the interaction between mismatch repair and genetic recombination observed in genetic studies.

Base Composition↗
PubMed1997

Sequential isologous organ transplantation in inbred rats: pancreaticoduodenal transplants.

A total of 847 inbred Lewis rats of mixed sex were used in this pancreaticoduodenal (Pd) donor aging study. Pd grafts were taken from 9- to 12-month-old donors and transplanted into 3-month-old recipients (thus, the first generation Pd graft, or 1 Pd). After 9 to 12 months, the same Pd grafts were again harvested and transplanted into 3-month-old rats (thus the 2 Pd generation). This cycle was repeated to obtain the 3, 4, and 5 Pd series. Sequential transplantation was able to extend the Pd grafts' mean survival time to 32 months for fourteen 4 Pd grafts, and to 39.2 months for four 5 Pd grafts (the longest lived graft survived for 42 months). The pancreas and duodenal sections of the grafts remained normal throughout the entire study. However, the aortic sections of the grafts (which were harvested to include the superior mesenteric and celiac arteries) all exhibited moderate to massive atherosclerotic changes by the 5 Pd mean survival age of 39.2 months. Such histological changes commenced even before 21 months of Pd graft age in some animals, gradually progressing to dilation of the aorta (and subsequent narrowing of aortic tributaries), as well as formation of an eggshell-like inner membrane shielding the aortic intima, by 42 months. Such atherosclerotic changes precluded transplantations beyond the 5 Pd series.

Age Factors↗
PubMed1997

Role of arginine vasopressin and corticotropin-releasing factor in mediating alcohol-induced adrenocorticotropin and vasopressin secretion in male rats bearing lesions of the paraventricular nuclei.

In male rats, lesions of the paraventricular nucleus (PVN) of the hypothalamus attenuate, but do not abolish, adrenocorticotropin (ACTH) secretion in response to acute alcohol injection. As the PVN is the major source of corticotropin-releasing factor (CRF) in the median eminence, this observation suggests that extra-PVN brain regions, and/or ACTH secretagogues other than CRF (e.g. arginine vasopressin (AVP)), mediate ACTH stimulation by alcohol. This hypothesis was tested by examining the effect of AVP immunoneutralization in PVN-lesioned (PVNx) rats. Removal of endogenous AVP diminished alcohol-evoked ACTH secretion in both sham-operated and PVNx animals, indicating that AVP from outside the PVN partially mediates the hypothalamic-pituitary-adrenal (HPA) axis response to alcohol. This led us to determine whether alcohol might also regulate AVP steady-state gene expression in the supraoptic nucleus (SON) and PVN, and/or CRF mRNA in the PVN and the central nucleus of the amygdala (AMY). In the magnocellular portion of the PVN, sham-operated animals showed significantly increased PVN levels of both CRF and AVP mRNAs 3 h after alcohol. In the SON, alcohol administration tended to decrease AVP gene expression in PVNx rats, while the drug increased AVP mRNA levels in the SON of sham-operated rats. AMY levels of CRF mRNA were unaffected by these manipulations. Finally, since the regulation of alcohol-induced AVP mRNA levels in the SON appeared to depend on the presence of the PVN, we measured peripheral levels of AVP in both sham-operated and PVNx animals after injection of vehicle or alcohol. Although AVP decreased in all groups, alcohol depressed AVP secretion to a greater extent in PVNx animals, suggesting that AVP systems are more sensitive to inhibition in the absence of the PVN. Our results demonstrate that although AVP of PVN origin may participate in regulating the stimulatory effect to AVP on ACTH secretion, AVP from areas other than the PVN also plays a role. Additionally, regulation of both AVP gene expression in the SON and secretion in the systemic circulation are altered in rats bearing lesions of the PVN.

Adrenocorticotropic Hormone↗
PubMed1997

Site-directed mutagenesis of the phosphocholine-binding site of human C-reactive protein: role of Thr76 and Trp67.

We have reported previously that residues Lys57, Arg58, and Trp67 of human C-reactive protein (CRP) contribute to the structure of the phosphocholine (PCh)-binding site. In this study, based on the three-dimensional structures of human CRP and serum amyloid P, we constructed an additional mutant, T76Y, to probe the structural determinants of the PCh-binding site of CRP. Binding properties of four mutant CRPs, K57Q/R58G, W67K, K57Q/R58G/W67K, and T76Y were compared. Wild-type (wt) and all mutant CRPs were purified by affinity chromatography on PCh-, pneumococcal C-polysaccharide (PnC)-, or phosphoethanolamine-conjugated agarose columns. Purified mutant CRPs, K57Q/R58G/W67K and T76Y failed to bind to solid phase, PCh-substituted BSA. They did, however, bind to immobilized PnC, although with substantially decreased avidity compared with wt CRP. W67K, K57Q/R58G/W67K, and T76Y CRP required a 10-fold higher Ca2+ concentration than wt CRP to bind PnC and exhibited decreased avidity for mAb EA4.1, which recognizes a Ca2+-dependent epitope. We conclude that Thr76 is a determinant of the PCh-binding site, probably interacting with the choline group. This conclusion is supported by recent crystallographic data indicating that this residue participates in the formation of a hydrophobic pocket that constitutes the binding site for choline. Trp67, Lys57, and Arg58 do not directly contact PCh, but appear to be required for the proper conformation of the binding site.

C-Reactive Protein↗
PubMed1997

Stress-wave-assisted transport through the plasma membrane in vitro.

BACKGROUND AND OBJECTIVE: Laser-induced stress waves have been shown to alter the permeability of the plasma membrane without affecting cell viability. The aim of the work reported here was to quantify the molecular uptake by cell cultures in vitro and determine optimal stress-wave parameters. STUDY DESIGN/MATERIALS AND METHODS: Human peripheral blood mononuclear cells were exposed to laser-induced stress waves in an experimental arrangement that eliminated interference from ancillary effects such as plasma, heat, or cavitation. A radiolabeled compound (tritiated thymidine) was used as the probe. RESULTS: Stress waves enhanced the diffusion of tritiated thymidine by inducing a transient permeabilization of the plasma membrane. Furthermore, maximum intracellular concentration (2 x 10(5) thymidine molecules/cell or 10% of the extracellular concentration) was reached with only 2-3 stress waves. CONCLUSION: Laser-induced stress waves provide an efficient method for delivering molecules through the plasma membrane into the cytoplasm of cells.

Cell Culture Techniques↗
PubMed1997

Structure of Semliki Forest virus core protein.

Alphaviruses are enveloped, insect-borne viruses, which contains a positive-sense RNA genome. The protein capsid is surrounded by a lipid membrane, which is penetrated by glycoprotein spikes. The structure of the Sindbis virus (SINV) (the type virus) core protein (SCP) was previously determined and found to have a chymotrypsin-like structure. SCP is a serine proteinase which cleaves itself from a polyprotein. Semliki Forest virus (SFV) is among the most distantly related alphaviruses to SINV. Similar to SCP, autocatalysis is inhibited in SFCP after cleavage of the polyprotein by leaving the carboxy-terminal tryptophan in the specificity pocket. The structures of two different crystal forms (I and II) of SFV core protein (SFCP) have been determined to 3.0 A and 3.3 A resolution, respectively. The SFCP monomer backbone structure is very similar to that of SCP. The dimeric association between monomers, A and B, found in two different crystal forms of SCP is also present in both crystal forms of SFCP. However, a third monomer, C, occurs in SFCP crystal form I. While monomers A and B make a tail-to-tail dimer contact, monomers B and C make a head-to-head dimer contact. A hydrophobic pocket on the surface of the capsid protein, the proposed site of binding of the E2 glycoprotein, has large conformational differences with respect to SCP and, in contrast to SCP, is found devoid of bound peptide. In particular, Tyr184 is pointing out of the hydrophobic pocket in SFCP, whereas the equivalent tyrosine in SCP is pointing into the pocket. The conformation of Tyr184, found in SFCP, is consistent with its availability for iodination, as observed in the homologous SINV cores. This suggests, by comparison with SCP, that E2 binding to cores causes major conformational changes, including the burial of Tyr184, which would stabilize the intact virus on budding from an infected cell. The head-to-tail contacts found in the pentameric and hexameric associations within the virion utilize in the same monomer surface regions as found in the crystalline dimer interfaces.

Amino Acid Sequence↗
PubMed1997

Vinculin and talin: kinetics of entry and exit from the cytoskeletal pool.

Vinculin and talin, two major components of focal contacts, exist in cytosolic and cytoskeletal pools. The kinetics of entry and exit of the two proteins between the two pools were investigated in normal and transformed cells. In cultured chick embryo fibroblasts, a fraction (2-5%) of the newly synthesized vinculin and talin reached maximal levels in the cytoskeleton in 30-45 min. Both proteins had 2-3 times shorter half-lives in the cytoskeletal pool (t1/2 = 6-7 h) than in the cytosolic pool (t1/2 = 14-15 h), which suggests that the incorporation of cytosolic vinculin and talin into the cytoskeleton does not involve a simple equilibrium between the two pools. However, after disruption of cell-to-substrate adhesion by trypsinization, an equilibrium in the incorporation between the two pools was transiently established, resulting in the use of the preexisting cytosolic pools of the two proteins during re-establishment of cell-to-matrix contacts. Viral transformation did not cause a significant change in the incorporation rates into the cytoskeleton. However, it decreased the half-lives of both proteins in the cytoskeletal pool (t1/2 = approximately 4 h) and in the cytosolic pool (t1/2 = 9-10 h). The increased turn-over rates of vinculin and talin in the cytoskeletal pool in transformed cells may contribute to the enhanced motility of transformed cells.

Animals↗
PubMed1997

Psychometric properties of the Eating Disorders Inventory (EDI-1) in a nonclinical Chinese population in Hong Kong.

OBJECTIVES: To evaluate the psychometric properties of the Chinese Eating Disorders Inventory (EDI-1) in a nonclinical population in Hong Kong. METHOD: 1,172 (females 606, males 566) Chinese undergraduates completed the Chinese EDI-1; 105 of them also completed the 12-item General Health Questionnaire (GHQ-12). RESULTS: In female subjects, the Chinese EDI-1 and its subscales met conventional standards of internal consistency, item-total, item-subscale, and subscale correlations, and exhibited an excellent degree of factorial integrity. The subscales discriminated among male, female, high Drive for Thinness, high Body Dissatisfaction, constitutionally slim, and Canadian female subjects. Female GHQ-12 cases and noncases were only distinguished by the Interpersonal Distrust, Interoceptive Awareness, and Ineffectiveness subscales. 3.3% of female subjects could be characterized as being pathologically weight preoccupied. DISCUSSION: This study provides preliminary evidence that the Chinese EDI-1 is an economical, reliable, and potentially useful self-report instrument for investigating the psychological and behavioral dimensions of eating disorders in Hong Kong. But further work is needed to evaluate its transcultural validity in clinical and less modernized Chinese populations.

Adolescent↗
PubMed1997

Beyond body image: the integration of feminist and transcultural theories in the understanding of self starvation.

OBJECTIVE: The present study represents an intersection between cross-cultural theorizing and teminist scholarship. It is an attempt to provoke as well as augment prevailing biomedical models that esteem fear of fatness as the primary motivation for voluntary starvation in anorexic women. METHOD: Recent studies of eating disturbance in both Eastern and Western societies are invoked to demonstrate the ways in which women straddling two worlds, be it generational, work-family, cultural or traditional and modern, may employ food denial as an instrumental means of negotiating the transition, disconnection, and oppression that they uniformly endure. RESULTS: A feminist/transcultural interpretation of the literature suggests that by construing anorexia nervosa as a body image disorder or Western culture-bound syndrome, extant models miss the broader contexts and varied meanings of food refusal. DISCUSSION: The implications of cross-disciplinary perspectives for theory building and treatment are discussed, acknowledging not only the gendered nature of eating disorders but their embodiment of power differentials as well.

Anorexia Nervosa↗