Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01178 (oxytocin)
 15,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of hormone binding on the reversible monomer in equilibrium dimer equilibrium of bovine neurophysins I or II in solution have been studied by sedimentation equilibrium measurements performed in conjunction with equilibrium dialysis experiments. Under normal solution conditions saturating amounts of oxytocin displace the neurophysin dimerization equilibrium toward the associated form of the protein to give a dimeric complex with two oxytocin molecules bound per dimer. Vasopressin exerts different influences on this oligomerization process. At low fractional saturation this ligand exhibits a behavior similar to oxytocin with a higher affinity for the neurophysin dimer than the monomer. But in contrast, at higher fractional saturation, vasopressin strongly displaces the aggregation equilibrium toward a monomeric complex bearing two vasopressin molecules. However, in the presence of a high concentration of LiCl two oxytocin molecules are bound per neurophysin protomer (10,000 daltons). These observations, together with earlier data for vasopressin binding, suggest that each neurophysin molecule possesses two structurally distinct hormone binding sites. These observations can be rationalized in a simple schematic model of hormone binding to neurophysin in which oxytocin favors a dimeric form with one hormone binding site available per 10,000 daltons while vasopressin favors the monomeric form with two hormone binding sites available per 10,000 daltons.
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PMID:Interactions of oxytocin and vasopressin with bovine neurophysins I and II. Effects of hormone binding on the protein quaternary structure: a simple model. 93 15

Protracted effect of [2-0-methyltyrosine]-deamino-1-carba-oxytocin, [2-0-methyltyrosine]-oxytocin and its dimeric form was studied on the mammary gland of lactating rat in vivo. Biphasic course of biological response found for monomers and slow onset of response observed for dimer led to the assumption that the substances behaved like hormonogens.
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PMID:Protracted milk-ejecting effect of some oxytocin analogues in rats. 108 3

Flexibility of various structural domains of neurophysin and neurophysin-neurohypophyseal hormone complexes has been investigated through the fast rotational motion of fluorophores in highly viscous medium. Despite seven intrachain disulfide links, it is shown that some domains of neurophysin remain highly flexible. Dimerization of neurophysin does not affect the structural integrity of the individual subunits, each subdomain being conformationally equivalent within each protomer of the unliganded dimer. The absence of heterogeneous fluorescence anisotropy precludes the existence of a dimer tautomerization equilibrium. Binding of the hormonal ligands to neurophysin dimer promotes a large conformational change over the whole protein structure as assessed by differential alterations of the flexibility-rigidity and intrasegmental interaction properties of domains that do not participate directly to the dimerization/binding areas. The order of free-energy coupling between ligand binding and protein subunit association has been evaluated. Data are consistent with a model in which the first mole of bound ligand stabilizes the dimer by increasing the intersubunit contacts while the second mole of ligand induces most of the described conformational change. Accordingly, the positive cooperativity between the two dimeric binding sites is linked mainly to the binding of the second ligand. The induced structural change is perceived differently by each subunit as assessed by opposite local motions of Tyr49 in each liganded protomer and leads to the formation of a dimeric complex with a global pseudospherical symmetry although containing domains of local asymmetry.
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PMID:Conformational flexibility of neurophysin as investigated by local motions of fluorophores. Relationships with neurohypophyseal hormone binding. 401 92

A neurophysin has been isolated from ostrich neurohypophyses using acid acetone extraction, salt fractionation and Sephadex G-75 chromatography. The crude neurophysin eluting from the Sephadex G-75 column was subjected to a) reverse-phase HPLC followed by Sephadex G-75 chromatography, b) DEAE-Sephadex A-50 chromatography or c) isoelectric focusing. The different homogeneous ostrich neurophysin fractions so obtained were compared i.t.o. amino acid composition, spectral properties, N-terminal amino acid residues and PAGE. They all revealed a single N-terminal Ala residue and displayed spectral properties (A280/A260 less than 1) which are typical of mammalian neurophysin-like polypeptides. Ultracentrifugation studies on purified ostrich neurophysin over a range of concentrations revealed a reversible concentration dependent association behaviour characterized by the presence of dimeric complexes at higher concentrations. Partial sequencing from the N-terminus revealed the molecule to be VLDV-like. The purified molecule was also submitted to CNBr fragmentation.
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PMID:Isolation and characterization of a neurophysin from ostrich neurohypophyses. 407 82

Previous hydrodynamic studies [Rholam, M., & Nicolas, P. (1981) Biochemistry 20, 5837-5843] have demonstrated that the dimerization of a neurophysin monomer (prolate ellipsoid with an axial ratio, due to asymmetry, of 5.2) results in a decreased asymmetry (axial ratio, due to asymmetry, of 3.6) as the consequence of a side-by-side association process. By a combination of hydrodynamic measurements, including the use of sedimentation velocity, viscometry, and fluorescence polarization spectroscopy, the influence of hormone binding on the shape and asymmetry properties of the neurophysin dimer was evaluated. The binding of ocytocin, vasopressin, and the tripeptide analogue of the N-terminal sequence of ocytocin, Cys(S-Me)-Tyr-Ile-NH2, results in an increase of S020,W and a decrease in both the reduced viscosity and rotational relaxation time of the bis-liganded dimeric species vs. the nonliganded form. The axial ratio (a/b) due to asymmetry of the ligand-bound dimers was found in each case to be equal to, or slightly greater than, 1.0, indicating a compact spherical shape (Stokes radius 21 A). The profound alteration on molecular dimensions observed upon ligand binding is shown to be the consequence of a ligand-induced conformational change and might explain the intradimeric binding sites positive cooperativity. It is tentatively proposed that the pseudospherical shape of the neurophysin-hormone complexes may enhance the stability of neurophysin and contribute to the prevention of leakage of neuropeptides through the membrane of neurosecretory granules. The data provide a remarkable example of a small protein with a high content in disulfide links and that undergoes conspicuous changes in conformation under the influence of nonapeptide, or tripeptide, ligands.
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PMID:Binding of neurohypophyseal peptides to neurophysin dimer promotes formation of compact and spherical complexes. 713 41

The interaction of bromophenol blue and related dyes with bovine neurophysin-I was studied by equilibrium dialysis and gel filtration, absorption and circular dichroism spectroscopy, and analytical ultracentrifugation. Binding isotherms for bromophenol blue showed positive cooperativity, with one strong site and one or more weaker sites present per polypeptide chain at pH 4 and an apparent increase in relative importance of the weaker sites of lower pH. Circular dichroism (CD) studies suggested displacement of bound dye by peptides that bind to the neurophysin hormone binding site. Titration of bound bromophenol blue indicated that the deprotonated dye was bound to the strong site with approximately 20-fold greater affinity than the protonated dye. The pH dependence of binding of bromophenol blue and of bromocresol purple, which has a higher pKa than bromophenol blue, indicated that binding was dependent on protonation of a protein residue with a pKa of 2.9. This residue was identified as a protein carboxyl, probably on an abnormal side chain, by studies of glycine ethyl ester modified neurophysin and carboxypeptidase-treated neurophysin. The presence of exciton interactions between bound dye molecules when only one dye was bound per polypeptide chain and analytical ultracentrifugation results indicated that dye was bound predominantly to the dimeric form of the protein. The implication of the data are discussed with respect to a kinetic model of dye-neurophysin interaction, used elsewhere in a study of neurophysin dimerization, that assumed interaction of protein monomers with protonated dye. Additionally, results are presented which suggest, in disagreement with conclusions based on the kinetic model, that there is a pH-dependent component of neurophysin dimerization which parallels low pH fluorescence and CD changes observed earlier.
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PMID:Interaction of bromophenol blue and related dyes with bovine neurophysin-I: use as a probe of neurophysin chemistry. 729 64

New methods have been developed for the synthesis of disulfide-bridged homo and hetero peptide dimers (both parallel and antiparallel), as exemplified in the oxytocin and deamino-oxytocin families. The linear sequences were assembled by 9-fluorenyl-methyloxycarbonyl (Fmoc) solid-phase synthesis techniques, with orthogonal protection for the two beta-thiols by appropriate combinations of S-[(N'-methyl-N'-phenylcarbamoyl)sulfernyl] (Snm), S-acetamido-methyl (Acm) and S-2, 4, 6-trimethoxybenzyl (Tmob) groups. Two octapeptide-resins gave rise to four different nonapeptide amides, which were brought together in defined ways to provide access to four of the six possible dimeric products. For each dimer, the first disulfide bond was formed in solution by a directed method, and then the second disulfide bond was formed, without purification of the intermediates, by iodine oxidation. Final isolated yields of the desired pure dimers were in the 20% to 40% range. Biological activities ranged from 0.2% to 6% that of oxytocin, depending on the assay, and were in some cases considerably protracted. These data are consistent with the hypothesis that dimers revert slowly to monomers under the testing conditions.
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PMID:Syntheses and biological activities of parallel and antiparallel homo and hetero bis-cystine dimers of oxytocin and deamino-oxytocin. 887 90

Activin A (beta A-beta A) and activin B (beta B-beta B) are related dimeric proteins that regulate numerous cellular activities. Activin activity is bioneutralized by follistatin, a specific and high-affinity binding protein. Recently, our group developed specific and sensitive enzyme-linked immunosorbent activin assays that do not detect either activin isoform when bound to follistatin, therefore, the assays are specific for biologically relevant ligands. Activin A is measurable in the serum of pregnant women (cross-sectional sample collection), while activin B is not detected in maternal serum. However, activin B is measurable in amniotic fluid and cord blood sera. The purpose of this study was to measure serum activin A, activin B, and follistatin prospectively in longitudinally collected samples during pregnancy. This study design offered observations of relative changes in serum hormone concentration with each person serving as an internal reference. Serum samples were collected bimonthly from seven pregnant women beginning within the second month of gestation, and up to, but not including, the onset of labor. Six of the seven women had normal labor and delivery. One patient required pitocin (an oxytocin agonist) for induction of labor which led to delivery. Activin A, activin B, total follistatin, free follistatin, human chorionic gonadotropin, estradiol, progesterone, FSH, and LH were measured in maternal serum samples using specific assays. Serum activin A levels increased in the final month of pregnancy in the six patients who delivered following normal labor (< 0.78 ng/ml (first trimester) to 1-6 ng/ml (term)). Activin B was not detected in any serum sample (< 0.78 pg/ml). Total serum follistatin (free follistatin, follistatin-activin, and follistatin-inhibin) increased 10- to 45-fold in the final month of pregnancy in four of the women undergoing normal labor (10 ng/ml (first trimester) to 100-450 ng/ml (final month)). Total follistatin was high and variable in two women throughout pregnancy. Total follistatin returned to basal serum concentration in three of the patients during the last 2 weeks of pregnancy. Free follistatin was detected throughout pregnancy (range < 2-35 ng/ml). Free follistatin represented a small percentage of the total follistatin throughout the time of pregnancy and did not rise coincident with the rise in total follistatin. Serum activin A and activin B were not detected during the entire course of pregnancy in the one patient who did not have normal labor and total follistatin did not rise in the last trimester of pregnancy. Gonadotropin and steroid hormones were measured in all patients and were within normative ranges for human pregnancy (inclusive of the non-laboring patient). The results suggest that immunodetectable activin A is present in the third trimester of pregnant women who have normal onset labor. The total follistatin assay results suggest that follistatin-activin (or -inhibin) complexes are upregulated during the third trimester of pregnancy. Importantly, activin A production exceeds the binding capacity of circulating follistatin. Because binding protein free activin A is biologically active we conclude that the activin A detected in late pregnancy is biologically relevant. The findings are consistent with our hypothesis that activin A is an endocrine factor during the last trimester of human pregnancy and may be involved in normal labor.
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PMID:Activin A and follistatin are dynamically regulated during human pregnancy. 907 73

Determination of the structure of the unliganded monomeric state of neurophysin is central to an understanding of the allosteric relationship between neurophysin peptide-binding and dimerization. We examined this state by NMR, using the weakly dimerizing H80E mutant of bovine neurophysin-I. The derived structure, to which more than one conformer appeared to contribute, was compared with the crystal structure of the unliganded des 1-6 bovine neurophysin-II dimer. Significant conformational differences between the two proteins were evident in the orientation of the 3,10 helix, in the 50-58 loop, in beta-turns, and in specific intrachain contacts between amino- and carboxyl domains. However, both had similar secondary structures, in independent confirmation of earlier circular dichroism studies. Previously suggested interactions between the amino terminus and the 50-58 loop in the monomer were also confirmed. Comparison of the observed differences between the two proteins with demonstrated effects of dimerization on the NMR spectrum of bovine neurophysin-I, and preliminary investigation of the effects of dimerization on H80E spectra, allowed tentative distinction between the contributions of sequence and self-association differences to the difference in conformation. Regions altered by dimerization encompass most binding site residues, providing a potential explanation of differences in binding affinity between the unliganded monomeric and dimeric states. Differences between monomer and dimer states in turns, interdomain contacts, and within the interdomain segment of the 50-58 loop suggest that the effects of dimerization on intrasubunit conformation reflect the need to adjust the relative positions of the interface segments of the two domains for optimal interaction with the adjacent subunit and/or reflect the dual role of some residues as participants both at the interface and in interdomain contacts.
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PMID:NMR analysis of the monomeric form of a mutant unliganded bovine neurophysin: comparison with the crystal structure of a neurophysin dimer. 1198 Apr 96

In vivo there appears to be a marked association between oestrogen levels and the expression of the oxytocin (OT) gene in most tissues. Transfection and DNA-protein binding experiments using high levels of either oestrogen receptor (ER)alpha or ERbeta imply a direct interaction of these transcription factors with the multiple hormone response element (HRE) at approximately -160 from the transcription start site of the OT gene in most species. In an extensive set of experiments, we show, using both transfection and protein-DNA binding, that low to moderate amounts of either oestrogen receptor, while being able to interact directly with a classic oestrogen response element (ERE) fail to interact with the human OT -160 HRE. Instead, this element, similar to its bovine counterpart, has a high affinity for the orphan receptors steroidogenic factor 1 and chicken ovalbumin upstream promoter transcription factor. Second, the human and bovine OT promoter can be made artificially responsive towards oestrogen in a cotransfection system over-expressing ERalpha or ERbeta, but not in cells expressing natural levels of these steroid receptors. Interestingly, nuclear extracts from both ERalpha-positive MCF7 cells and ERalpha-negative MDA-MB231 cells both contain a transcription factor which binds specifically to both the hOT-HRE element and to a classic ERE, and which has orphan receptor-like binding properties rather than those of an oestrogen receptor. Together, these and other results suggest that oestrogen action in vivo on the OT gene in all species is more likely to involve a DNA-independent mechanism than classic direct interactions with dimeric oestrogen receptors.
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PMID:The affinity and activity of the multiple hormone response element in the proximal promoter of the human oxytocin gene. 1204 22


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