Neuropeptide Y receptors from calf brain: effect of crude Conus venom preparations on [3H]NPY binding

Formation of angiotensin-(1-7) from angiotensin II by the venom of Conus geographus

The binding of [3H]angiotensin II to AT(1) receptors on Chinese Hamster Ovary cells expressing the human AT(1) receptor (CHO-AT(1) cells) is potently inhibited by venoms of the marine snails Conus geographus and C. betulinus. On the other hand, the binding of the nonpeptide AT(1) receptor-selective antagonist [3H]candesartan is not affected but competition binding curves of angiotensin II and the peptide antagonist [Sar(1),Ile(8)]angiotensin II (sarile) are shifted to the right. These effects resulted from the breakdown of angiotensin II into smaller fragments that do not bind to the AT(1) receptor. In this context, angiotensin-(1-7) is the most prominent fragment and angiotensin-(1-4) and angiotensin-(1-5) are also formed but to a lesser extent. The molecular weight of the involved peptidases exceeds 50 kDa, as determined by gel chromatography and ultrafitration.

High affinity displacement of [(3)H]NPY binding to the crude venom of conus anemone by insect neuropeptides

The venom from Conus anemone contains a protein, named ANPY toxin, which displayed high affinity (IC(50) in nanomolar range) to neuropeptide Y (NPY), [Leu(31), Pro(34)]NPY, peptide YY, pancreatic polypeptide, the Y(1) antagonist 1229U91, and C-terminal NPY fragments. N-terminal fragments and the free acid form of NPY did not bind to ANPY. The truncated NPY fragments displayed very low affinity to Y(1) receptors and partially inhibited [(3)H]NPY binding to anti-NPY antiserum. Several insect neuropeptides, the sequences of which related to the C-terminal fragments of NPY, were observed to bind with similar affinity or even 20 times higher (Lom-MS and Scg-NPF) affinity than NPY. In contrast, no significant binding of these insect peptides was observed for Y(1) receptors and anti-NPY antiserum. Therefore, ANPY can be viewed as an acceptor that binds with very high affinity to a broad spectrum of vertebrate and invertebrate neuropeptides that share a similar C-terminal amino acid sequence.

Identification of tyrosine sulfation in Conus pennaceus conotoxins alpha-PnIA and alpha-PnIB: further investigation of labile sulfo- and phosphopeptides by electrospray, matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure MALDI mass spectrometry

Liquid chromatography/electrospray ionization mass spectrometry was used to investigate the peptide composition of the venom of Conus pennaceus, a molluscivorous cone shell from the Red Sea. Based on observed M(r)s, this venom contained all known conotoxins previously isolated and identified from this species. Interestingly, the doubly protonated species of only two of these conotoxins, alpha-PnIA and alpha-PnIB, showed additional related ions at +40 m/z (+80 Da), indicating the presence of either sulfation or phosphorylation in both components. High-performance liquid chromatographic (HPLC) fractions containing these two conotoxins were examined by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry in both positive and negative ion modes, as well as by MALDI high-energy collision-induced dissociation. These experiments established the presence of a single sulfated tyrosine residue within both alpha-PnIA and alpha-PnIB. Hence their post-translationally modified sequences are GCCSLPPCAANNPDY(S)C-NH2 (alpha-PnIA) and GCCSLPPCALSNPDY(S)C-NH2 (alpha-PnIB). This assignment was supported by comparison of their mass spectral behavior with that of known sulfated and phosphorylated peptides. This data clarified further the distinguishing features of the ionization and fragmentation of such modified peptides. Selective disulfide folding of synthetic alpha-PnIB demonstrated that both sulfated and non-sulfated toxins co-elute on reversed-phase HPLC and that alpha-PnIB possesses the same disulfide connectivity as other 'classical' alpha-conotoxins reported previously.

Non-competitive binding of the nonpeptide antagonist BIBP3226 to rat forebrain neuropeptide Y1 receptors

[3H]Neuropeptide Y labelled neuropeptide Y receptors in rat forebrain membranes as a homogenous class of high-affinity sites. Between 80 and 85% of these receptors showed high affinity for Y1-selective antagonists such as (R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine amide (BIBP3226). While competitive in functional studies, BIBP3226 produced parallel shifts of the Scatchard plots of [3H]neuropeptide Y saturation binding in rat forebrain membranes. Mechanisms which are routinely invoked to explain non-competitive binding do not apply to BIBP3226. Wash-out experiments, involving successive treatment of the membranes with BIBP3226, buffer (wash-out step) and [3H]neuropeptide Y, argue against irreversible or a pseudo-irreversible binding of the antagonist. Allosteric inhibition is also unlikely since BIBP3226 did not affect the rate of dissociation of [3H]neuropeptide Y in isotope dilution experiments. The non-hydrolyzable guanine nucleotide, 5'-guanylylimidodiphosphate (Gpp(NH)p), abolished the binding of [3H]neuropeptide Y and increased its rate of dissociation in isotope dilution experiments. This suggests that the initial [3H]neuropeptide Y-receptor association is a low affinity process and that the observed binding of [3H]neuropeptide Y is related to the formation of a ternary [3H]neuropeptide Y-receptor-G protein complex. Two- or even multistate models (in which BIBP3226 could potentially behave as an inverse agonist) could therefore be needed to explain the non-competitive antagonism of BIBP3226 in broken cell preparations.

High-affinity binding of [3H]neuropeptide Y to a polypeptide from the venom of Conus anemone

Venom preparation from Conus anemone contains a component that binds radiolabeled neuropeptide Y ([3H]neuropeptide Y) with high affinity (KD = 2.9 nM +/- 0.2 nM, Bmax = 15.2 +/- 0.5 pmol/mg protein). Binding of [3H]neuropeptide Y to the venom component is displaced with nanomolar affinity of unlabeled human and porcine neuropeptide Y, porcine [Leu31-Pro34]neuropeptide Y, peptide YY, avian and bovine pancreatic polypeptide, and the (18-36) and (25-36) C-terminal fragments from neuropeptide Y. No displacement is found with the (1-24) N-terminal neuropeptide Y fragment, human secretin, porcine dynorphin A and Boc-DAKLI (bolton Hunter coupled dynorphin A analog kappa ligand) nor with the non-peptide neuropeptide Y receptor antagonist BIBP3266. Gel filtration chromatography and denaturing (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) show that the [3H]neuropeptide Y-binding component is very likely a single-chain polypeptide with a molecular mass of 18.5 kDa.