Increase in expression of P2X1 receptors in the atria of patients suffering from dilated cardiomyopathy

P2X1 receptors are ATP-sensitive ligand-gated cation-selective channels abundant in smooth muscle tissues such as bladder and vas deferens. They have also been detected in the central and peripheral nervous system and in heart tissue. We have earlier reported distinct changes in the expression of the PX1 subtype of P2X receptors in hearts of patients suffering from dilated cardiomyopathy (DCM). The study was, however, based on Western blots from only five DCM samples and three control hearts. Moreover, the antibody was directed against a peptide derived from the sequence of rat P2X1. In the present project we have examined larger groups of both DCM and control hearts (n = 14 and 11, respectively). Furthermore, the antibody used in this paper differs significantly from the one used in our previous report. The present antibody was raised against an 18-residue peptide sequence (Lys 68-84 Val) derived from the human P2X1 sequence. Most of the label in the Western blots was concentrated over a triplet of bands migrating with an apparent Mr of about 45,000. Quantitative densitometry indicated that this band was more strongly expressed (by approximately 80%) in DCM hearts compared with the controls.

Expression and localisation of stanniocalcin 1 in rat bladder, kidney and ovary

Bony fish use the glycoprotein hormone stanniocalcin (STC) to counteract hypercalcaemia. This is achieved through dual mechanisms involving gill calcium uptake inhibition and stimulation of renal inorganic phosphate reabsorption. Human STC (hSTC-1) shows considerable homology with both rat and mouse STC (mSTC) and their mRNA is expressed in a wide range of tissues. In fish, STC is produced by endocrine glands known as the corpuscles of Stannius but in mammals the widespread expression is suggestive of a paracrine rather than an endocrine role. In order to determine the distribution and strucutral characteristics of hSTC-1, the recombinant protein was expressed in bacteria, purified by metal-ion affinity chromatography, and a study was made of the likely epitopes for raising an antibody. This novel hSTC-1 antibody was used to test the purification protocol. Since the role of mammalian STC is largely unknown, the specific distribution of STC needed to be addressed. To test the specificity of the antibody, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blotting was undertaken in homogenised rat bladder, ovary and kidney.

Identification and localisation of ATP P2X receptors in rat midbrain

P2X receptors that are gated by extracellular ATP are among the few known examples of ligand-gated cation-selective channels. There have been seven cloned proteins identified to date as members of the P2X receptor family in a wide range of tissues from the peripheral and central nervous systems and from many species. To determine the distribution of the P2X subtypes in the rat midbrain, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blotting was combined with immunolocalisation using confocal microscopy. Subtypes P2X1-6 were detected in the periaqueductal gray area and the ependymal layer bordering the ventricle with a widespread distribution.

Localisation of P2X receptors in human salivary gland epithelial cells and human embryonic kidney cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis/Western blotting and immunofluorescence

Human salivary gland epithelial cells, a continuous cell line derived from an irradiated human salivary gland and human embryonic kidney cell line human embryonic kidney (HEK)293 were examined for the purpose of establishing whether they expressed endogenous P2X ionotropic receptors at any stage in their cycles. HSG cells were found to express P2X1-6 subtypes using both Western blotting and immunofluorescence labeling. HEK293 cells had no detectable levels of P2X1-3 and P2X6 under normal circumstances along with very low levels of P2X4 and P2X5 but when the cells were grown past confluence then all subtypes were expressed on the surface membrane with the exception of P2X2. The results are discussed in terms of the likely influence of ATP acting as an intercellular signaling molecule.

Analysis of novel P2X subunit-specific antibodies in rat cardiac and smooth muscle

P2X receptors are cation-selective channels gated by extracellular adenosine triphosphate (ATP). There are relatively few known types of ligand-gated receptors. In vertebrates they include acetylcholine (Ach), 5-hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA), glycine, and glutamate as well as ATP. Ach, 5-HT, GABA and glycine ligand-gated receptors are related in evolutionary terms, while glutamate and ATP receptors form separate groups. There have been seven cloned proteins identified to date as members of the P2X receptor family in a wide range of cells and species. We have carried out hydropathy investigations and sequence comparisons of each of the seven subunits in order to examine the putative transmembrane and cysteine-rich extracellular domains. Probable locations of disulphide bridges are consistent with there being two separate extracellular folding domains. Assessment of the putative surface-accessible regions was used to select small localised amino acid segments in nonglycosylated regions for raising antibodies against each of the P2X receptor subunits. To test the specificity of these novel P2X receptor antibodies and their presence in cardiac and smooth muscle, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blotting was undertaken in homogenised rat heart, bladder, kidney, and vas deferens.

Structure study of osteostatin PTHrP[Thr107](107-139)

The structure of chicken osteostatin or parathyroid hormone-related protein (PTHrP) (residues 107-139) containing an Ala/Thr substitution at the N-terminus was studied using two-dimensional proton NMR spectroscopy in an aqueous environment. Osteostatin is a separate circulating domain responsible for a range of activities related to the modulation of bone formation as well as keratinocyte proliferation. Anti-mitogenic properties of osteostatin have been detected in breast cancer cells and cytosolic calcium is used by osteostatin to signal in some neurons through a non-PTH receptor, unlike the separate circulating N-terminal domain. A structural basis for the activity is presented with particular emphasis given to the conformation of the bioactive segment 107-111, forming part of a finger-like projection capable of binding to the non-PTH receptor both in the presence and absence of the remainder of the molecule which appears simply to act as a largely globular carrier.

Vesicle-associated proteins and P2X receptor clusters at single sympathetic varicosities in mouse vas deferens

1. Antibodies against vesicle-associated proteins of the SNARE complex (syntaxin (AbS), SNAP 25 (AbS25), synaptobrevin (VAMP; AbV) and the alpha1B subunit of calcium channels (Abalpha(1B)) were located with respect to sympathetic varicosities (labelled with the ubiquitous vesicle proteoglycan antibody AbSV2) and to clusters of P2X receptor subunits (labelled with antibodies AbP2X(1) to AbP2X(6)). In addition, these receptor clusters were located with respect to Schwann cells labelled with antibodies to S100 (AbS100).2. The spatial relation between proteins of the SNARE complex and calcium channels was determined. AbS25 patches ranged from 250-500 nm in size and were often colocalised with smaller AbS patches (250-350 nm). Abalpha(1B) patches (300-700 nm diameter) were always coincidental with AbS patches. AbV patches (400-1000 nm in diameter) also coincided with AbS patches.3. The spatial relation between different P2X subunit clusters and varicosities labelled with AbSV2 was ascertained. Large (500-700 nm diameter) AbP2X(1) receptor clusters were found colocalised with many (91%) AbSV2 labelled varicosities, although small diameter (250-350 nm) AbP2X(1) clusters occurred at random over the muscle. Small AbP2X(2) clusters were found uniquely in the vicinity of AbSV2 labelled varicosities, but were not entirely coincidental with these. Small AbP2X(3) receptor clusters were found in close association with AbSV2 labelled nerves. Small diameter AbP2X(4) clusters (250-350 nm) were found throughout the muscle with some of these coincidental with AbSV2 labelling. Small diameter AbP2X(5) (250-350 nm) cluster labelling was found in juxtaposition to strings of AbSV2 labelled varicosities but were not coincidental with these. Small (250-350 nm) diameter AbP2X(6) clusters were also found in close juxtaposition to AbSV2 labelled nerves.4. The spatial relation between different P2X subtype clusters and Schwann cells labelled with AbS100 was examined. Both AbP2X(1) and AbP2X(3) receptor clusters were found in close apposition with AbS100, with clusters of the former sometimes coincidental with patches of the latter. On the other hand AbP2X(2) was found in association with AbS100 at low levels while AbP2X(4) labelling was generally not coincidental with AbS100. AbP2X(5) and AbP2X(6) labelling was often colocalised with AbS100 labelling.5. The spatial relation between proteins of the SNARE complex and P2X(1) receptors was determined. Large AbP2X(1) clusters were often found apposed by AbS, AbV and Abalpha(1B) labelled patches.6. Destruction of the sympathetic varicosities with 6-hydroxydopamine led to the virtual disappearance of AbP2X(2) labelling, but to a large increase in the number of small AbP2X(1) receptor clusters and a reduction in the number of large AbP2X(1) clusters. AbS100 Schwann cell labelling was largely unaffected.7. These observations are interpreted as showing that most terminal sympathetic varicosities possess active zones about 250-700 nm diameter, delineated by syntaxin, SNAP 25 and N-type calcium channels and that synaptic vesicles are concentrated at these sites as indicated by the localisation of VAMP. Most of these terminal varicosities possess active zones that are precisely apposed to large clusters of P2X(1) receptors. However small clusters of P2X(2) to P2X(6) receptors can be found that are near the strings of varicosities but not usually coincidental with them except P2X(3). The functional significance of this arrangement of vesicle-associated proteins and P2X receptors for the generation of synaptic potentials at the autonomic neuromuscular junction is discussed.

P2X (purinergic) receptor distributions in rat blood vessels

The distribution of purinergic (P2X1 and P2X2) receptors on smooth muscle cells in relation to autonomic nerve varicosities in rat blood vessels has been determined using immunofluorescence and confocal microscopy. P2X1 and P2X2 receptors were visualised using rabbit polyclonal antibodies against the extracellular domain of the receptors and varicosities visualised using a mouse monoclonal antibody against the ubiquitous synaptic vesicle proteoglycan SV2. Two size classes of P2X1 receptor clusters were observed on the smooth muscle cells of mesenteric, renal, and pulmonary arteries as well as in the aorta and in veins: a large approximately elliptical cluster 1.32+/-0.21 microm long and 0.96+/-0.10 microm in diameter; and a smaller spherical cluster with a diameter of 0.32+/-0.05 microm. The latter occurred throughout the media of arteries of all sizes, whereas the former were restricted to the adventitial surface of the media and to endothelial cells, except for the pulmonary artery, in which large receptor clusters were found throughout the media of the vessel. At the adventitial surface, the large clusters are in general located beneath SV2 labelled varicosities. None of the small clusters was associated with varicosities. Three-dimensional reconstruction of the P2X and SV2 labelling at individual varicosities showed that the varicosities were immediately apposed to the P2X receptor clusters. P2X2 receptors were located on nerves and on endothelial cells. They were also found in low density on the smooth muscle cells in the media. These observations are discussed in relation to the mechanism of purinergic transmission to the smooth muscle cells of blood vessels.

Development of P2X receptor clusters on smooth muscle cells in relation to nerve varicosities in the rat urinary bladder

Postnatal development of the distribution of different isoforms of purinergic (P2X) receptors on smooth muscle cells in relation to the development of the innervation of the cells by nerve varicosities in the rat urinary bladder has been determined with immunofluorescence and confocal microscopy. Antibodies against the extracellular domains of the P2X(1) to P2X(6) receptors were used to detect the receptors in the bladder. Several other antibodies were used to identify sympathetic varicosities and Schwann cells. At one day postnatal (D1) there were few strings of varicosities denoting isolated axons, with most axons confined to large nerve trunks. Small size clusters of P2X(1) to P2X(6) receptor subtypes (about 0.4 microm diameter) were observed in the muscle which were independent of each other, and sometimes juxtaposed to the rare isolated varicosity strings. At D4 large numbers of strings of varicosities could be discerned throughout the detrusor. Most of these clouds of small P2X(1) to P2X(6) receptor clusters in their immediate vicinity. Some of these were colocalised with the varicosities, which were of parasympathetic origin as they failed to counter-stain with antibodies to tyrosine hydroxylase. Up to D14 there was a gradual coalescence of many of the isolated P2X(1-6) small receptor clusters so that they became colocalized, often at varicosities. Most of the varicosities in isolated strings possessed receptor clusters at this time. By D21 it was rare to find varicosity strings in the detrusor that were not either in close juxtaposition with P2X small receptor clusters or possessing such clusters in colocalization. However, large numbers of small P2X receptor clusters, many of which consisted of a mixture of isoforms, could be found spatially unrelated to nerve varicosities throughout the detrusor muscle. In the adult, single axons were either coextensive with one or more isoforms of P2X receptor clusters or these were immediately juxtaposed to the axons so that is was rare to find a varicosity that did not possess a receptor cluster. However, different combinations of colocalized P2X receptor isoforms could still be discerned in small clusters unrelated to varicosities. These observations are discussed in relation to the mechanism of formation of the receptor clusters and their migration beneath parasympathetic varicosities during development.

Ligand recognition sites on P2X receptors studied by quantitative autoradiography of [3H]alpha,beta-methylene-ATP binding in rat brain

The specificity of alpha, beta-methylene-ATP for P2X receptor binding sites in the CNS has been examined by testing the effects of several ATP analogues and other ATP-related substances on the binding of 10 nM [3H]alpha,beta-methylene-ATP to 20 microns thick sections of fresh-frozen rat brain. The labelling of the putative P2X receptor binding sites by [3H]alpha,beta-methylene-ATP was evaluated by quantitative densitometry. [3H]alpha,beta-methylene-ATP binding was strongly inhibited by two close ATP analogues, 3'-O-(trinitrophenyl)-adenosine-5'-triphosphate and beta,gamma-imido-ATP (IC50 2.5 microM). beta,gamma-Methylene-ATP was, however, less potent (< 50% inhibition at 25 microM). Inosine-5'-triphosphate, guanosine-5'-triphosphate, uridine-5'-triphosphate, and cytidine-5'-triphosphate were practically inactive up to concentrations of 100 microM. Periodate oxidised ATP and 1, N6-etheno-ATP produced < 50% inhibition at 100 and 500 microM concentrations, respectively. Cations (K+, Rb+, Cs+, and Mg2+ at 5 mM and Na+ at 150 mM) reduced [3H]alpha,beta-methylene-ATP binding by no more than 50%. Several agents known to interact with Ca2+- and/or ATP-related cationic channels (Cd2+, glibenclamide, dantrolene, nifedipine, and thapsigargin) had no effect. We conclude that [3H]alpha,beta-methylene-ATP at low nanomolar concentrations binds to a site that has very strict structural requirements and is pharmacologically similar to ATP P2X receptors.

Alterations in the expression of P2X1 receptors in failing and nondiseased human atria

This is the first report of the analysis of the ATP-specific P2X1 receptor subunit in human hearts. We have examined homogenate samples of human left atria for the presence of P2X1 receptors using Western blots. Anti-P2X1 immunoreactivity was detected in populations of nondiseased atria as well as in atria from explanted hearts from patients with terminally failing heart conditions such as dilated cardiomyopathy. At least three groups of P2X1 immunoreactive proteins were detected in the Western blots with approximate molecular mass values of 50, 70, and 160 kDa. We report changes in expression of their 50 and 70 kDa components. These changes may be related to the type of deficit in these hearts since the changes have been observed in hearts with decreased ejection fractions characteristic of dilated cardiomyopathy.

Solution structure of parathyroid hormone related protein (residues 1-34) containing an Ala substituted for an Ile in position 15 (PTHrP[Ala15]-(1-34))

The structure of human parathyroid hormone (PTH) related protein (residues 1-34) containing an Ala substituted for an Ile in position 15 was studied by two-dimensional proton nuclear magnetic resonance spectroscopy. This mutant retains quite high levels of adenylate cyclase activity based on slightly reduced PTH receptor binding capacity. Three segments of helix were revealed extending from His5 to Lys11, Lys13 to Arg19, and from Phe22 to Thr33/Ala34, with a decided kink between the first two helices around Gly12. N- and C-terminal helices were stabilized by charged and hydrophobic side chain interactions between His5 and Glu30, Asp17 and both His9 and His25, and between Leu8 and Ala29, resulting in a globular molecule occupying a single conformation. While the structure of the entire mid-molecule region differed greatly from the structure of the native peptide, the structure of both N- and C-terminal regions remains essentially unaltered. The residues responsible for initiating signal transduction in the mutant are located in the vicinity of the residues responsible for receptor binding. The C-terminal amphipathic helix forming the receptor binding site exhibits reduced binding as a result of the closely applied N-terminal signal transduction-activating region. Although not contributing directly to receptor binding, the N-terminal region can sterically affect hormone binding through modifications to certain N-terminal side chains.

Structural motif and characteristics of the extracellular domain of P2X receptors

Seven sequences of the proteins recently cloned from rat tissues and identified as P2X receptors are examined. Their putative transmembrane and extracellular domains and the most probable locations of disulphide bridges are discussed. Some surface accessible regions are identified and the structure of the putative ATP binding domain is discussed in the light of known selectivities and physiological characteristics of individual P2X subunits. The summarised information and the theoretical considerations regarding the protein structure of P2X receptors have been used to select amino acid sequences for raising antibodies against the P2X1 receptor subunit. Initial results suggest that, in rat brainstem, P2X1 receptor subunits are found on a distinct subpopulation of neuronal perikarya in distributions consistent with distributions of known alpha,beta-methylene-ATP autoradiography and physiological effects of purinoceptor activation.

Pseudosubstrate flexibility in chicken smooth muscle myosin light chain kinase

Chicken smooth muscle myosin light chain kinase pseudosubstrate is contained within the C-terminal region of the sequence MLCK(774-807)amide. It forms a helical conformation which interacts with the connecting peptide contained within the N-terminal portion of the sequence. These regions are linked by a well-defined turn around Ser-787 which supports a model of pseudosubstrate regulation involving the hinging of the pseudosubstrate or autoregulatory recognition sequence away from the active site of the catalytic core following the binding of calmodulin to the kinase.

Evidence that the PTH receptor binding site on PTHrP(1-34) can hinge at Arg19/Arg20

The structure of the biologically-active mutant of human parathyroid hormone related protein (residues 1-34) containing an Ala substituted for a His in position 9 reveals two segments of helix extending from Glu4 to Lys13 and from Phe22 to Ala34, with a reverse turn from Gln16 to Arg19. The C-terminal region contains the bulk of the PTH receptor binding site in an amphipathic helix and is capable of hinging at Arg19/Arg20. The region of the molecule containing full antagonist properties is thus confined to the C-terminal helix.

Structure of the pseudosubstrate recognition site of chicken smooth muscle myosin light chain kinase

The structure of the chicken smooth muscle myosin light chain kinase pseudosubstrate sequence MLCK(774-807)amide was studied using two-dimensional proton NMR spectroscopy. Resonance assignments were made with the aid of totally correlated and nuclear Overhauser effect spectroscopy. A distance geometry algorithm was used to process the body of NMR distance and angle data and the resulting family of structures was further refined using dynamic simulated annealing. The major structural features determined include two helical segments extending from Asp-777 to Lys-785 and from Arg-790/Met-791 to Trp-800 connected by a turn region from Leu-786 to Asp-789 enabling the helices to interact in solution. The C-terminal helix incorporates the bulk of the pseudosubstrate recognition site which is partially overlapped by the calmodulin binding site while the N-terminal helix forms the bulk of the connecting peptide. The demonstrated turn between the helices may assist in enabling the autoregulatory or pseudosubstrate recognition sequence to be rotated out of the active site of the catalytic core following calmodulin binding.

Structure of prejunctional receptor binding analog of human neuropeptide Y dimer ANA-NPY

Human neuropeptide Y (NPY) analog ANA-NPY or [L17, Q19, A20, A23, L28, L31]NPY (13-36)-amide binds weakly to postjunctional receptors to raise blood pressure but binds tightly to prejunctional receptors to inhibit neurotransmitter release. ANA-NPY forms a well-conserved anti-parallel helical structure overlapping E23-Y36 with strong amphipathic character. The C-terminal portions of the monomers are better defined than the N-terminal ends. The N-terminal helices extend only from D16-E23/L24. The prejunctional receptor-specific binding site is confined within the C-terminal helices while the residues responsible for partial binding to the postjunctional receptors are located in the more disordered N-terminal segments.

Conformation of a tetradecapeptide epitope of myelin basic protein

The peptide AcAla-Ser-Gln-Lys-Arg-Pro-Ser-Gln-Arg-His-Gly-Ser-Lys-Tyr, which comprises the first 14 residues of the acetylated N-terminus of myelin basic protein, is an epitopic site for two monoclonal antibodies to the human protein. The conformations of the tetradecapeptide in aqueous solutions were investigated employing high-resolution 1H- and 13C-NMR spectroscopy. Two-dimensional techniques were used to assign the spectra observed from both nuclei. Nuclear-Overhauser-effect data, amide proton temperature coefficients, 13C spin-lattice relaxation times, distance geometry calculations and dynamic simulated annealing provided evidence that the solution conformations of the tetradecapeptide included a nascent alpha-helix in the N-terminal segment, and a loop extending from Ser7 to Ser12 that bring His10 and Tyr14 into close proximity.

Structure of the presynaptic (Y2) receptor-specific neuropeptide Y analog ANA-NPY

Neuropeptide Y analog ANA-NPY or [Leu-17, Gln-19, Ala-20, Ala-23, Leu-28, Leu-31]NPY(13-36)-amide binds to postjunctional or Y1 receptors to raise blood pressure and to prejunctional or Y2 receptors to inhibit neurotransmitter release. ANA-NPY affects Y2 receptors in the same way as intact NPY but exhibits far less potent effects on Y1 receptors. The structure of ANA-NPY was examined using two-dimensional proton nuclear magnetic resonance spectroscopy. Complete assignment of all backbone and side chain hydrogens was accomplished with totally correlated spectroscopy (TOCSY) experiments providing through-bond 1H-1H connectivities, and nuclear Overhauser effect spectroscopy (NOESY), providing the through-space and sequential backbone connectivities. The tertiary solution structure of the peptide was performed using distance geometry and dynamic simulated annealing. ANA-NPY exhibits a helical structure with strong amphipathic character with a bend around Glu-24 indicating that the C-terminal segment 25-35 forms a single alpha-helical motif.

Stabilized NMR structure of the hypercalcemia of malignancy peptide PTHrP[Ala-26](1-34)amide

The structure of the biologically active mutant PTHrP[Ala-26](1-34)amide in 10% trifluoroethanol was studied by two-dimensional proton NMR spectroscopy. Complete assignments of all backbone and side chain hydrogens were made with the aid of totally correlated and nuclear Overhauser effect spectroscopy. The NMR data were utilized in the distance geometry algorithm (DIANA) and the resulting family of structures further refined using dynamic simulated annealing (X-PLOR). The major structural features include two segments of alpha-helix extending from Glu-4 to Lys-13 and from Phe-21/Phe-22 to Ala-34, with a turn from Gln-16 to Arg-19 and a hinge around Ser-14/Ile-15. A close resemblance to the structure of PTH(1-34)amide in water was noted. A comparison of the structural features common to PTH and PTHrP in different solvents was made which enabled the key structural features likely to be involved in PTH receptor binding to be identified.

Stabilized structure of the presynaptic (Y2) receptor-specific neuropeptide Y analog N-acetyl[Leu-28,Leu-31]NPY(24-36)

Neuropeptide Y analog N-acetyl[Leu-28,Leu-31]NPY(24-36)-amide binds specifically to prejunctional or Y2 receptors acting to inhibit neurotransmitter release. The structure of this biologically active mutant was studied by two-dimensional proton nuclear magnetic resonance spectroscopy. Assignments of all backbone and side chain hydrogens were made by using totally correlated spectroscopy (TOCSY) experiments providing through-bond 1H-1H connectivities, and nuclear Overhauser effect spectroscopy (NOESY), which provided through-space and sequential backbone connectivities. Structure analysis of the peptide was performed using distance geometry and dynamic simulated annealing revealing the presence of a helical structure exhibiting an amphiphilic character and slight constriction in the segment 24-29.

A novel neuropeptide Y analog, N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36), with functional specificity for the presynaptic (Y2) receptor

We have carried out functional and in vitro studies on a novel analog of neuropeptide Y which shows selectivity for the prejunctional or neuropeptide Y Y2 receptor. In anaesthetised rats N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36) attenuates cardiac vagal action (a prejunctional or neuropeptide Y Y2 action) and has no significant pressor effects (postjunctional or neuropeptide Y Y1 action). In the human neuroblastoma cell line (SMS-KAN) which expresses and endogenous Y2-like neuropeptide Y receptor, N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36) competes with peptide YY for binding sites with an IC50 of 0.5 +/- 0.1 nM. In contrast in a fibroblast Chinese hamster ovary cell line which expresses the cloned human neuropeptide Y Y1 receptor and is used to study changes in cytosolic calcium evoked by (a neuropeptide Y Y1 effect), N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36) showed no activity even at high concentrations. The steric structure for this novel compound has been determined using proton nuclear magnetic resonance (NMR) spectroscopy and it is consistent with the C-terminal end of published structures of neuropeptide Y. We suggest acetylation and amino acid substitutions stabilise the molecule and allow it to bind only to the neuropeptide Y Y2 receptor.

NMR solution structure of human parathyroid hormone(1-34)

The aqueous solution structure of the biologically-active N-terminal domain of human parathyroid hormone (residues 1-34) was studied by two-dimensional proton nuclear magnetic resonance (2D NMR) spectroscopy, distance geometry, and dynamic simulated annealing. Unambiguous NMR assignments of all backbone and side chain hydrogens were made with the aid of totally correlated spectroscopy experiments, which provided through-bond 1H-1H connectivities, and nuclear Overhauser effect spectroscopy, which provided through-space and sequential backbone connectivities. The NMR data acquired were utilized in a distance geometry algorithm to generate a family of structures which were then refined using dynamic simulated annealing. The major structural feature evident is alpha-helix extending from residues Glu4 to Lys13 and from Val21 to Gln29 with a turn incorporating Asn16-Glu19 resulting in a quite globular C-terminal domain with a hydrophobic core comprising Leu15, Leu18, Trp23, and Val31. Structure-activity studies are interpreted in terms of the deduced conformation of the PTH structure with particular reference to the likely PTH receptor binding site formed primarily by the bulk of the C-terminal helix.

Stabilized NMR structure of human parathyroid hormone(1-34)

The structure of the biologically-active N-terminal region of human parathyroid hormone, PTH(1-34), was investigated in the presence of 10% trifluoroethanol using two-dimensional proton NMR spectroscopy, distance geometry and dynamic simulated annealing. Complete assignments of all backbone and side chain hydrogens were made with the aid of totally correlated spectroscopy (TOCSY) experiments, providing through-bond 1H-1H connectivities, and NOESY providing through-space and sequential backbone connectivities. Distance and angle constraints were used in the distance geometry algorithm DIANA II to generate a family of structures satisfying all inputs. The lowest energy structures were further refined using the dynamic-simulated-annealing protocol XPLOR 3. The major structural features evident in 10% trifluoroethanol are two segments of alpha-helix extending from residues Glu4 to Lys14/His14 and Ser17 to Asp30. A short length of unordered structure joined the two spans of helix. The structures of the N-terminal regions (4-13/14) agreed closely with the structure found in human parathyroid-hormone-related protein (PTHrP)(1-34) obtained earlier by Ray, Barden and Kemp [19]. However, PTHrP(16-19) exhibited a reverse turn which is incorporated in an extended helix in PTH. The consequent interactions between several hydrophobic residues in the C-terminal region in PTHrP are absent in PTH. Moreover, the turn in PTHrP(22-25) at the start of the C-terminal helix is present as a more standard loop of helix in PTH. Comparisons between the structures of the two hormones has enabled the probable location and structure of the PTH receptor-binding site to be placed in the segment of amphiphilic alpha-helix (24-31).