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)

Binding and spectroscopic properties of ostrich neurophysins were examined with emphasis on the behavior of Tyr-35, a residue that provides a potential probe of the monomer-monomer interface and of allosteric interrelationships between this region and the binding site. Mesotocin-associated ostrich neurophysin was found to bind oxytocin and related peptides with affinities comparable to the mammalian proteins, but induced a significantly different optical activity in bound peptides than the mammalian proteins. Gel-filtration studies indicated higher dimerization constants for the ostrich neurophysins than for the bovine neurophysins. Consistent with this, Tyr-35 was found to be largely buried, as monitored by tyrosine titration and lack of reactivity towards tetranitromethane under non-denaturing conditions. Reaction of Tyr-35 of the mesotocin-associated protein with tetranitromethane under denaturing conditions, followed by refolding, allowed isolation of an active product with an altered interface region as partially evidenced by its titration properties and consistent with its markedly altered CD spectrum. Comparison of the CD spectra of the modified and native proteins and analysis of pH effects indicated the contribution of Tyr-35 to an unusual 237 nm band in the mesotocin-associated protein. Small shifts in the 350 nm CD band of nitrated Tyr-35 on binding peptide and apparent effects of nitration on the induced optical activity in bound peptide provided evidence of at least weak structural communication between Tyr-35 and the binding site. However, no significant effect of nitration on binding affinity was observed, suggesting that, in the mesotocin-associated protein, the region around residue 35 is not a stringent modulator of the thermodynamic behavior of the binding site.
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PMID:Binding and spectroscopic properties of ostrich neurophysins. Probing the role of residue 35 at the monomer-monomer interface. 142 29

The primary structure of an elephant neurophysin, homologous to vasopressin-associated neurophysins, is reported. The protein contains a Tyr for Asn substitution at position 75, a position in direct contact with residues 77 and 78 of the monomer-monomer interface. This Tyr residue therefore serves as a potential reporter of the path involved in the long-range linkage between peptide binding and dimerization in this system. NMR studies of the protein in unliganded and liganded states demonstrated normal dimerization properties and the expected increase in dimerization associated with binding peptide. In keeping with an elevated pKa of 11.1 assigned to Tyr-75 by UV spectrophotometric titration, the NMR signals from the 3,5 and 2,6 ring protons of Tyr-75 were shifted 0.3 and 0.2 ppm upfield, respectively, relative to their positions in small peptides, indicating significant shielding and/or hydrogen bonding. The Tyr-75 ring proton signals narrowed slightly, with no discernible change in chemical shift, on conversion from dimer to monomer in the unliganded state. Ring protons of Tyr-49, distant from the monomer-monomer interface, but adjacent to the peptide-binding site, were markedly perturbed by dimerization, in accord with their behavior in bovine neurophysins. The results suggest that the secondary and tertiary structure of the region 75-78 is largely unchanged by dimerization, and argue against an important role for this region in dimerization-mediated conformational changes that alter the binding site in the unliganded state.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Amino acid sequence and properties of vasopressin-associated elephant neurophysin. 782 4

The effects of the peptide hormone oxytocin (OT) are mediated by the oxytocin receptor, which is a member of the G-protein-coupled receptor family. Defining differences between the binding of agonists and antagonists to the OTR, at the molecular level, is of fundamental importance to understanding OTR activation and to rational drug design. Previous reports have indicated that the N-terminus of the OTR is required for OT binding. The aim of this study was to identify which individual residues within the N-terminal domain of the human OTR provided these OT binding epitopes. A series of truncated OTRs and mutant receptor constructs with systematic alanine substitution were characterized with respect to their pharmacological profile and intracellular signaling capability. Although a number of residues within the OTR will be required for optimal OT-OTR interaction, our data establish that Arg(34) within the N-terminal domain contributes to high-affinity OT binding. Removal of Arg(34) by truncation or substitution resulted in a 2000-fold decrease in OT affinity. In addition, we show that the arginyl at this locus is required for high-affinity binding of agonists in general. However, the importance of Arg(34) is restricted to agonist interaction with the OTR, as it was not required for binding peptide antagonist or non-peptide antagonist. It is noteworthy that the corresponding Arg in the related rat V(1a) vasopressin receptor is also required for high-affinity agonist binding. This study defines, at the molecular level, the role of the N-terminus of the OTR in high-affinity agonist binding and identifies a key residue for this function.
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PMID:Agonist-specific, high-affinity binding epitopes are contributed by an arginine in the N-terminus of the human oxytocin receptor. 1195 56

Pulsatile neuropeptide secretion is associated with burst firing patterns; however, intracellular signaling cascades leading to bursts remain unclear. We explored mechanisms underlying burst firing in oxytocin (OT) neurons in the supraoptic nucleus in brain slices from lactating rats. Application of 10 pm OT for 30 min or progressively rising OT concentrations from 1 to 100 pm induced burst firing in OT neurons in patch-clamp recordings. Burst generation was blocked by OT antagonist and ionotropic glutamate receptor blockers or tetanus toxin. Blocking G-protein activation with suramin or intracellular GDP-beta-S, but not intracellularly administered antibody against the OT-receptor (OTR) C terminus, blocked bursts. Moreover, pretreatment of slices with pertussis toxin, an inhibitor of G(i/o)-proteins, did not block OT-evoked bursts, suggesting that G(i)/G(o) activation is unnecessary for burst generation. Thus, we further examined G alpha(q/11)-associated signaling pathways in OT-evoked bursts. Inhibition of phospholipase C or RhoA/Rho kinase did not block bursts. Activation of G betagamma subunits using myristoylated G betagamma-binding peptide (mSIRK) caused bursts, whereas intracellularly loaded antibody against G beta subunit blocked OT-evoked bursts. Blocking Src family kinase, but not phosphatidylinositol 3-kinase, occluded OT-evoked bursts. Similar to the effects of OT on EPSCs, mSIRK inhibited tonic EPSCs and elicited EPSC clustering. Finally, suckling caused dissociation of OTRs and G beta subunits from G alpha(q/11) subunits shown by coimmunoprecipitation and immunocytochemistry, supporting crucial roles for OTRs and G betagamma subunits in the milk-ejection reflex. We conclude that G betagamma subunits play a dominant role in burst firing evoked by applied OT or by suckling.
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PMID:Dominant role of betagamma subunits of G-proteins in oxytocin-evoked burst firing. 1731 86