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H Yuan

Publications and source records attributed to H Yuan.

At least 163 records · Page 9Linked to original sources
PubMed1995

Solution structure of the oxidized 2[4Fe-4S] ferredoxin from Clostridium pasteurianum.

Following the recently developed approach to the solution structure of paramagnetic high-potential iron-sulfur proteins, the three-dimensional structure in solution of the oxidized Clostridium pasteurianum ferredoxin has been solved by 1H-NMR. The X-ray structure is not available. The protein contains 55 amino acids and two [4Fe-4S] clusters. In the oxidized state, the clusters have S = 0 ground states, but are paramagnetic because of thermal population of excited states. Due to the somewhat small size of the protein and to the presence of two clusters, approximately 55% of the residues have at least one proton with a non-selective T1 smaller than 25 ms. The protein has thus been used as a test system to challenge the present paramagnetic NMR methodology both in achieving an extended assignment and in obtaining a suitable number of constraints. 79% of protein protons have been assigned. Analogy with other ferredoxins of known structure has been of help to speed up the final stages of the assignment, although we have shown that this independent information is not necessary. In addition to dipolar connectivities, partially detected through tailored experiments, 3JHN-H alpha, H-bond constraints and dihedral angle constraints on the Cys chi 2 angles have been generated by using a recently derived Karplus-type relationship for the hyperfine shifts of cysteine beta CH2 protons. In total, 456 constraints have been used in distance geometry calculations. The final quality of the structures is satisfactory, with root-mean-square deviation values of 66 pm and 108 pm for backbone and heavy atoms, respectively. The resulting structure is compared with that of Clostridium acidi urici ferredoxin [Duée, E. D., Fanchon, E., Vicat, J., Sieker, L. C., Meyer, J. & Moulis, J.-M. (1994) J. Mol. Biol. 243, 683-695]. The two proteins are very similar in the overall folding, secondary structure elements and side-chain orientations. The C alpha root-mean-square deviation values between the X-ray-determined C. acidi urici ferredoxin structure and the conformer with lowest energy of the C. pasteurianum ferredoxin family is 78 pm (residues 3-53). Discrepancies in residues 26-28 may arise from the disorder observed in the X-ray structure in that region.

Amino Acid Sequence↗
PubMed1995

Relevance of oxidative stress to the limited replicative capacity of cultured human diploid cells: the limit of cumulative population doublings increases under low concentrations of oxygen and decreases in response to aminotriazole.

Human diploid cells, TIG-7, were serially cultivated under 1%, 5% or 21% (air) oxygen. The limit of their cumulative population doublings was extended by 16% or 10% under 1% or 5% oxygen, respectively, as compared with that under 21% oxygen. When TIG-7 cells were serially cultivated in the presence of 10 mM or 20 mM 3-amino-1H-1,2,4-triazole, an inhibitor of catalase scavenging hydrogen peroxide, the limit of their cumulative population doublings was shortened by 4.4% or 14.4%, respectively, as compared with untreated cells. In addition, long-term, rather than short-term, exposure of TIG-7 cells to aminotriazole retarded cell growth. Treatment with aminotriazole caused decreases not only in catalase activity but also in superoxide dismutase activity and reduced glutathione concentration, and an increase in glutathione peroxidase activity. These results suggest that the limit of the cumulative population doublings of human diploid cells is extended or shortened under decreasing or increasing oxidative stress, respectively. Oxidative stress may be relevant to replicative capacity, and a causative factor for oxidative stress may be hydrogen peroxide.

Amitrole↗
PubMed1995

Interaction of the von Willebrand factor (vWF) with collagen. Localization of the primary collagen-binding site by analysis of recombinant vWF a domain polypeptides.

The von Willebrand factor (vWF) mediates platelet adhesion to the vascular subendothelium by binding to collagen, other matrix constituents, and the platelet receptor glycoproteins Ib/IX and IIb/IIIa. Although substantial progress has been made in defining vWF structure-function relationships, there are conflicting data regarding the location of its collagen-binding site(s). Possible collagen-binding sites have been localized in the A1 and A3 domains of vWF. To study the proposed binding sites, we have expressed cDNA sequences encoding the A1 and A3 domains of vWF in Escherichia coli and purified the resulting proteins from bacterial inclusion bodies. In addition, a chimeric molecule containing residues 465-598 of the vWF A1 domain polypeptide (vWF-A1) fused in frame to residues 1018-1114 of the vWF A3 domain polypeptide (vWF-A3) was also expressed. Each of the three recombinant proteins purified as a monomer and contained a single disulfide bond. As previously reported (Cruz, M. A., Handin, R. I., and Wise, R. J. (1993) J. Biol. Chem. 268, 21238-21245), recombinant vWF-A1 inhibited ristocetin-induced platelet agglutination, but did not compete with vWF multimers for collagen binding. In contrast, vWF-A3 inhibited the binding of multimeric vWF to immobilized collagen, but did not inhibit ristocetin-induced platelet agglutination. Metabolically labeled vWF-A3 bound to immobilized collagen in a saturable and reversible manner with a Kd of 1.8 x 10(-6) M. The vWF-A1/A3 chimera was bifunctional. It inhibited vWF binding to platelet glycoprotein Ib/IX with an IC50 of 0.6 x 10(-6) M and inhibited vWF binding to collagen with an IC50 of 0.5-1.0 x 10(-6) M. These results, taken together, provide firm evidence that the major collagen-binding site in vWF resides in the A3 domain.

Base Sequence↗
PubMed1995

Species difference in the resistibility of embryonic fibroblasts against oxygen-induced growth inhibition.

The growth of fibroblasts, which were isolated from human, rabbit, rat, mouse, and chick embryos, was inhibited partially under 50% oxygen and nearly completely under 95% oxygen. There was species difference in the resistivity of these cells against oxygen-induced growth inhibition. The extent of the resistivity was in the following order: chick cells > rat cells > human cells > rabbit cells approximately mouse cells. The order of their ability to recover from oxygen-induced growth inhibition was similar to the above order of species. There was also species difference in their antioxidant enzyme activities, including superoxide dismutase, catalase, and glutathione peroxidase activities, and their reduced glutathione concentration. Chick cells, having the highest resistivity against oxygen-induced growth inhibition, were at the lowest activity levels of antioxidant enzymes and at the highest concentration level of reduced glutathione. The species difference in resistivity against oxygen-induced growth inhibition seems to depend on the reduced glutathione concentration, but not on the antioxidant enzyme activities.

Animals↗
PubMed1995

Cross-clade neutralization of primary isolates of human immunodeficiency virus type 1 by human monoclonal antibodies and tetrameric CD4-IgG.

We have tested three human monoclonal antibodies (MAbs) IgG1b12, 2G12, and 2F5) to the envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1), and a tetrameric CD4-IgG molecule (CD4-IgG2), for the ability to neutralize primary HIV-1 isolates from the genetic clades A through F and from group O. Each of the reagents broadly and potently neutralized B-clade isolates. The 2F5 MAb and the CD4-IgG2 molecule also neutralized strains from outside the B clade, with the same breadth and potency that they showed against B-clade strains. The other two MAbs were able to neutralize a significant proportion of strains from outside the B clade, although there was a reduction in their efficacy compared with their activity against B-clade isolates. Neutralization of isolates by 2F5 correlated with their possession of the LDKW motif in a segment of gp41 near the membrane-spanning domain. The other two MAbs and CD4-IgG2 recognize discontinuous binding sites on gp120, and so no comparison between genetic sequence and virus neutralization was possible. Our data show that a vaccine based on the induction of humoral immunity that is broadly active across the genetic clades is not impossible if immunogens that express the epitopes for MAbs such as 2F5, 2G12, and IgG1b12 in immunogenic configurations can be created. Furthermore, if the three MAbs and CD4-IgG2 produce clinical benefit in immunotherapeutic trials in the United States or Europe, they may also do so elsewhere in the world.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Regulation by vascular endothelial growth factor of human colon cancer tumorigenesis in a mouse model of experimental liver metastasis.

To investigate the relationship between angiogenesis and hepatic tumorigenesis, we examined the expression of vascular endothelial growth factor (VEGF) in 8 human colon carcinoma cell lines and in 30 human colorectal cancer liver metastases. Abundant message for VEGF was found in all tumors, localized to the malignant cells within each neoplasm. Two receptors for VEGF, KDR and flt1, were also demonstrated in most of the tumors examined. KDR and flt1 mRNA were limited to tumor endothelial cells and were more strongly expressed in the hepatic metastases than in the sinusoidal endothelium of the surrounding liver parenchyma. VEGF monoclonal antibody administration in tumor-bearing athymic mice led to a dose- and time-dependent inhibition of growth of subcutaneous xenografts and to a marked reduction in the number and size of experimental liver metastases. In hepatic metastases of VEGF antibody-treated mice, neither blood vessels nor expression of the mouse KDR homologue flk-1 could be demonstrated. These data indicate that VEGF is a commonly expressed angiogenic factor in human colorectal cancer metastases, that VEGF receptors are up-regulated as a concomitant of hepatic tumorigenesis, and that modulation of VEGF gene expression or activity may represent a potentially effective antineoplastic therapy in colorectal cancer.

Animals↗
PubMed1995

Distribution of occupied and unoccupied estrogen receptors in the rat brain: effects of physiological gonadal steroid exposure.

In vitro autoradiographic methods have been developed for selective measurement of occupied and unoccupied estrogen receptors (ERs) in brain tissue sections. Addition of protamine sulfate traps unoccupied ERs in the tissue sections, allowing them to be detected after a short period of incubation with labeled estrogen. Occupied ERs are assessed, after washing in buffer without protamine to eliminate unoccupied receptor, by incubating the sections for 2 h at 37 C to exchange isotopically labeled steroid for the endogenous unlabeled ligand. Total ER binding capacity is estimated by summing the values for occupied and unoccupied ER. In all brain regions of normal females, ER occupation is low at estrus, reflecting the very low levels of circulating estradiol present at this stage of the estrous cycle, rising to approximately 50% of binding capacity at proestrus. By contrast, in intact males ER occupation varies considerably between brain regions, from a high of 55% of binding capacity in the bed nucleus of the stria terminalis to a low of 21% in the hypothalamic arcuate nucleus. Gonadectomy or treatment of intact males with the aromatase inhibitor 4-hydroxy androstenedione greatly reduces or eliminates ER occupation, depending on the brain region. In both sexes, changes in levels of endogenous gonadal steroids have little effect on total (occupied plus unoccupied) ER concentrations, with the exception of the hypothalamic ventromedial nucleus of the female, in which total ER concentration declines at estrus. These results are consistent with the hypothesis that local aromatization may be the primary determinant of regional ER occupation in the brain of the male rat, in contrast to the female, in which high levels of ER occupation are found only during the preovulatory estrogen surge. Although physiological changes in circulating estradiol and aromatizable androgen concentrations induce large changes in ER occupation, they have little effect on total ER content in most regions of the brain, suggesting that previous reports of changes in ER messenger RNA levels under different conditions of gonadal steroid exposure may not be directly reflected in steady state levels of the cognate receptor site.

Animals↗
PubMed1995

Changes in prevalence, intensity of infection and morbidity due to Schistosoma japonicum infection in a community following a single treatment with praziquantel.

A repeat survey for schistosomiasis japonica was carried out in Sisan community 1 year after chemotherapy with praziquantel was stopped. Prevalence of infection had fallen from 43.7 to 10.2%, intensity (population geometric mean) had dropped from 6.3 to 0.6 eggs per gram of stool and morbidity decreased significantly.

Adolescent↗
PubMed1994

Interaction between a novel F9-specific factor and octamer-binding proteins is required for cell-type-restricted activity of the fibroblast growth factor 4 enhancer.

Understanding how diverse transcription patterns are achieved through common factor binding elements is a fundamental question that underlies much of developmental and cellular biology. One example is provided by the fibroblast growth factor 4 (FGF-4) gene, whose expression is restricted to specific embryonic tissues during development and to undifferentiated embryonal carcinoma cells in tissue culture. Analysis of the cis- and trans-acting elements required for the activity of the previously identified FGF-4 enhancer in F9 embryonal carcinoma cells showed that enhancer function depends on sequences that bind Sp1 and ubiquitous as well as F9-specific octamer-binding proteins. However, sequences immediately upstream of the octamer motif, which conform to a binding site for the high-mobility group (HMG) domain factor family, were also critical to enhancer function. We have identified a novel F9-specific factor, Fx, which specifically recognizes this motif. Fx formed complexes with either Oct-1 or Oct-3 in a template-dependent manner. The ability of different enhancer variants to form the Oct-Fx complexes correlated with enhancer activity, indicating that these complexes play an essential role in transcriptional activation of the FGF-4 gene. Thus, while FGF-4 enhancer function is octamer site dependent, its developmentally restricted activity is determined by the interaction of octamer-binding proteins with the tissue-specific factor Fx.

Animals↗
PubMed1993

LISREL modeling of high density lipoprotein cholesterol (HDL) levels in male twins.

Based on the LISREL modeling approach for data from monozygotic (MZ) and dizygotic (DZ) twins [Heath et al., 1989; Neale and Cardon, 1992], the hypothesized variance of the logarithm of high density lipoprotein cholesterol due to additive genetic factors was estimated to equal 19% for males. Unobserved common environment accounted for 32% of the variance of log HDL. Both estimates controlled for body mass, alcohol consumption, and smoking. The model had very strong goodness-of-fit indices.

Alcohol Drinking↗
PubMed1993

Specific binding of [125I]iodomelatonin in pigeon and quail spleen membrane preparations and effect with hydrocortisone-treatment.

[125I]Iodomelatonin binding sites were studied in the spleens of pigeon and quail. Scatchard analyses of the membrane preparations collected at midday (12:00) revealed an equilibrium dissociation constant (Kd) of 250 +/- 74 pmol.L-1 and a maximal number of binding sites (Bmax) of 13.4 +/- 1.8 fmol/mg protein in the pigeon spleen and Kd = 390 +/- 132 pmol.L-1, Bmax = 21.3 +/- 3.7 fmol/mg protein in the quail spleen. Circadian studies indicated that spleens collected at midnight (24:00) had 53% and 70.9% less [125I]iodomelatonin binding sites than the samples collected at midday in the pigeon and quail, respectively. Specificity studies showed only melatonin and 6-chloromelatonin had significant inhibition to [125I]iodomelatonin binding. Hydrocortisone 15 mg.kg-1 x d-1 im for 5 d selectively increased [125I] iodomelatonin binding sites in pigeon spleen. These results suggest that spleen is a site of melatonin action outside the brain.

Animals↗
PubMed1993

[Clinical observation of the effect of pretreatment with nifedipine in preventing oxygen free radicals in the cardiopulmonary release bypass operation].

The effect of pretreatment with nifedipine in preventing oxygen free radicals release was observed in the cardiopulmonary bypass (CPB) operation. Twenty cases were divided into two groups for comparison. Nifedipine (0.6 mg/kg) was given to the test group. MDA, XO, UA and SOD were measured. These examinations were taken at pre-aortic clamping, 15 min after aortic clamping, and 30, 60, 120, 180 min after reperfusion. The results indicated that pretreatment with nifedipine reduced oxygen free radicals release in the CPB operation.

Adolescent↗
PubMed1992

Alternative structures for alternating poly(dA-dT) tracts: the structure of the B-DNA decamer C-G-A-T-A-T-A-T-C-G.

The X-ray crystal structure of the decamer C-G-A-T-A-T-A-T-C-G has been solved with two contrasting cations, Ca2+ and Mg2+. Crystals with calcium are space group P2(1)2(1)2(1), cell dimensions a = 38.76 A, b = 40.06 A, and c = 33.73 A, and diffract to 1.7-A resolution. Crystals with magnesium have the same space group, cell dimensions a = 38.69 A, b = 39.56 A, and c = 33.64 A, and diffract to 2.0 A. Their structures were solved independently by molecular replacement, beginning with idealized Arnott B-DNA geometry. The calcium structure refined to R = 17.8% for the 3683 reflections greater than 2 sigma, with 404 DNA atoms, 95 solvent peaks, and 1 Ca(H2O)7(2+) ion. The magnesium structure refined to R = 16.5% for the 1852 reflections greater than 2 sigma, with 404 DNA atoms, 62 solvent peaks, and 1 Mg(H2O)6(2+) ion. The two structures are virtually identical and are isostructural with C-G-A-T-C-G-A-T-C-G [Grzeskowiak et al. (1991) J. Biol. Chem. 266, 8861-8883] and C-G-A-T-T-A-A-T-C-G [Quintana et al. (1992) J. Mol. Biol. 225, 375-395]. Comparison of C-G-A-T-A-T-A-T-C-G with C-G-C-A-T-A-T-A-T-G-C-G [Yoon et al. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 6332-6336] shows that the expected alternation of twist angles is found in the central A-T-A-T-A-T region of the decamer (A-T small, T-A large), but the minor groove remains wide at the center, rather than narrow. Minor groove narrowing is produced, in these two structures, not by overwinding of the helix, but by an increase in base pair propeller. This analysis confirms the concept that poly(dA-dT).poly(dA-dT) is polymorphous, with different local conformations possible in different local environments.

Base Sequence↗
PubMed1992

The mitochondrial F1ATPase alpha-subunit is necessary for efficient import of mitochondrial precursors.

The mitochondrial import and assembly of the F1ATPase subunits requires, respectively, the participation of the molecular chaperones hsp70SSA1 and hsp70SSC1 and other components operating on opposite sides of the mitochondrial membrane. In previous studies, both the homology and the assembly properties of the F1ATPase alpha-subunit (ATP1p) compared to the groEL homologue, hsp60, have led to the proposal that this subunit could exhibit chaperone-like activity. In this report the extent to which this subunit participates in protein transport has been determined by comparing import into mitochondria that lack the F1ATPase alpha-subunit (delta ATP1) versus mitochondria that lack the other major catalytic subunit, the F1ATPase beta-subunit (delta ATP2). Yeast mutants lacking the alpha-subunit but not the beta-subunit grow much more slowly than expected on fermentable carbon sources and exhibit delayed kinetics of protein import for several mitochondrial precursors such as the F1 beta subunit, hsp60MIF4 and subunits 4 and 5 of the cytochrome oxidase. In vitro and in vivo the F1 beta-subunit precursor accumulates as a translocation intermediate in absence of the F1 alpha-subunit. In the absence of both the ATPase subunits yeast grows at the same rate as a strain lacking only the beta-subunit, and import of mitochondrial precursors is restored to that of wild type. These data indicate that the F1 alpha-subunit likely functions as an "assembly partner" to influence protein import rather than functioning directly as a chaperone. These data are discussed in light of the relationship between the import and assembly of proteins in mitochondria.

Biological Transport↗
PubMed1992

Bipartite signal for read-through suppression in murine leukemia virus mRNA: an eight-nucleotide purine-rich sequence immediately downstream of the gag termination codon followed by an RNA pseudoknot.

The pol gene of murine leukemia virus and other mammalian type C retroviruses is expressed by read-through suppression of an in-frame UAG codon which separates the gag and pol coding regions. In this study, we have analyzed the sequence requirements for read-through suppression by placing different portions of wild-type and mutant viral sequences from the gag-pol junction between reporter genes and testing transcripts of these constructs for suppression in reticulocyte lysates. We find that the read-through signal is contained within the first 57 nucleotides on the 3' side of the UAG codon. Our results indicate that the identities of six conserved bases in the eight-nucleotide, purine-rich sequence immediately downstream of the UAG codon are critical for suppression, as is the existence of a pseudoknot structure spanning the next 49 nucleotides. Thus, read-through suppression depends on a complex, bipartite signal in the mRNA.

Animals↗
PubMed1992

The identification of 125I-labelled iodomelatonin-binding sites in the testes and ovaries of the chicken (Gallus domesticus).

The existence of 125I-labelled iodomelatonin-binding sites in chicken ovaries and testes was investigated. The specific binding of 125I-labelled iodomelatonin to chicken ovarian and testicular tissue satisfies all the criteria for a binding site. It was rapid, stable, saturable, reversible, specific and of high affinity. Equilibrium studies showed that total and non-specific binding increased over a range of 5-150 pmol 125I-labelled iodomelatonin/l tested, with specific binding reaching saturation towards the middle range of radioligand concentrations. Scatchard analyses indicated a dissociation constant (Kd) of 36.5 +/- 5.3 pmol/l (means +/- S.E.M.) in the membrane preparations of chicken testes at the middle point in the period of light and a maximum number of binding sites (Bmax) of 0.93 +/- 0.40 fmol/mg protein (n = 6). In membrane preparations of chicken ovaries, the Kd was 102.2 +/- 27.3 pmol/l and the Bmax was 2.77 +/- 0.38 fmol/mg protein (n = 6). Equilibrium and kinetic dissociation constants in the picomolar range indicate high-affinity and physiologically relevant 125I-labelled iodomelatonin-binding sites. Competitive inhibition studies determined the following order of relative potency for inhibition of 125I-labelled iodomelatonin-binding to chicken gonadal membranes: 6-chloromelatonin greater than melatonin greater than N-acetylserotonin much much greater than 5-hydroxytryptamine, tryptamine, 5-methoxytryptophol, 1-acetylindole-3-acetic acid, 5-hydroxyindole-3-acetic acid and L-tryptophan. The presence of 125I-labelled iodomelatonin-binding sites suggests a direct pineal-gonadal connection in the chicken.

Animals↗