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R Schwyzer

Publications and source records attributed to R Schwyzer.

At least 37 records · Page 2Linked to original sources
PubMed1987

Membrane-assisted molecular mechanism of neurokinin receptor subtype selection.

Based on the observed membrane structures of substance P, physalaemin, and eledoisin, preferred conformations, orientations and accumulations of 13 mammalian neurokinins and non-mammalian tachykinins were estimated and compared with pharmacologic and selective binding data taken from the literature. Principal site affinities and relative affinities supported the view that neurokinins bind to three principal mammalian sites: the NK-1 (preferring substance P), the NK-2 (preferring neurokinin A), and the NK-3 site (preferring neurokinin B). Strong hydrophobic membrane interaction of the C-terminal message segment as a perpendicularly oriented alpha-helical domain correlated with NK-1 selection. Electrostatic accumulation of the peptide at the anionic fixed charge layer of the membrane without hydrophobic interaction through a helix correlated with NK-2 preference. Electrostatic repulsion by the anionic fixed charge layer correlated with NK-3 selection. Thus, neurokinin receptor selection is guided by the same principles as opioid receptor selection. Membrane catalysis of specific agonist--receptor interactions may prove to be a quite general phenomenon, and the membrane structure of a peptide more important for its structure--activity relationship than its crystal structure or its mixture of conformers in solution or in vacuo.

Amino Acid Sequence↗
PubMed1986

Molecular mechanism of opioid receptor selection.

Preferred conformations, orientations, and accumulations of 26 opioid peptides on lipid membranes were estimated and compared with pharmacologic and selective binding data taken from the literature. Interaction with mu-receptors was governed by the net positive charge effective at the message domain of the agonist peptides z(eff) as the Boltzmann term ez(eff) that determines relative accumulation on anionic biologic membranes. Selection for delta-receptors was reduced by z(eff) and correlated with e-z(eff). Selection for kappa-receptors was governed by the peptide amphiphilic moment A. A pronounced scalar magnitude A and almost perpendicular orientation of the N-terminal message domain as an alpha-helix were favorable for kappa-site selection. Potencies as kappa-agonists and binding affinities correlated with A X ez(eff). The classical site selectivity caused by the receptor requirements for a complementary fit of the agonist to the discriminator site is thus crucially supplemented by a selection mechanism based on peptide membrane interactions (membrane requirements). In the model presented here, the delta-site is exposed to the aqueous compartment surrounding the target cell at a distance comparable to or greater than the Debye-Hückel length and is in a cationic vicinity. The mu-site is exposed to the anionic fixed-charge compartment of the membrane in aqueous surroundings. The kappa-site is buried in a more hydrophobic membrane compartment close to the fixed-charge compartment. The relative accumulation of the opioid message domains in these compartments is determined by the address domains and constitutes a major part of the site selection mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1986

Estimated conformation, orientation, and accumulation of dynorphin A-(1-13)-tridecapeptide on the surface of neutral lipid membranes.

Equilibrium thermodynamic and kinetic estimations were used to confirm the rather unusual conformation, orientation, and accumulation of dynorphin A-(1-13)-tridecapeptide (dynorphin1-13) on the surface of neutral lipid membranes, as observed by Erne et al. [Erne, D., Sargent, D. F., & Schwyzer, R. (1985) Biochemistry 24, 4261-4263]. I started from the premise that the most stable conformation of molecularly disperse peptides in contact with the hydrophobic phase of a membrane is helical [Henderson, R. (1979) Soc. Gen. Physiol. Ser. 33, 3-15]. Calculation of the Gibbs free energy difference for the transfer of increasing numbers m of N-terminal residues of dynorphin1-13 from their random-coil conformation in water to their alpha-helical conformation in a hydrophobic phase, with the values provided by Von Heijne and Blomberg [Von Heijne, G., & Blomberg, C. (1979) Eur. J. Biochem. 97, 175-181], showed an energy minimum at m = 9 that corresponded to the observed apparent association constant of 9 X 10(4) L/mol. This confirmed our experimental observations. The orientation of dynorphin1-13 in the interphase was estimated by calculation of the molecular amphiphilic moment A. This force vector was defined in analogy to the "helical" and "structural" hydrophobic moments of Eisenberg et al. [Eisenberg, D., Weiss, R. M., & Terwilliger, T. C. (1982) Nature (London) 299, 371-374]. It takes into account the segregation of hydrophobic and hydrophilic residues with respect to the center of the alpha-helix. A peptide located in a hydrophobic-hydrophilic gradient experiences a torque that tends to orient A in a direction perpendicular to the surfaces of equal hydrophobicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynorphins↗
PubMed1986

Membrane lipid phase as catalyst for peptide-receptor interactions.

Catalysis of ligand-receptor interactions is proposed as an important function of the lipid phase of the cell membrane. The catalytic mechanism is deduced from observed specific interactions of amphiphilic peptides with artificial lipid bilayers. In our model a direct ligand-receptor reaction is replaced by multiple sequential steps including surface accumulation of charged ligands, ligand-membrane interactions, and ultimately binding to the receptor itself. By dividing the total free energy of binding among several steps, the energy per step, including the intrinsic receptor interaction energy, is kept to moderate values. The model thereby yields simple explanations for the large apparent association constants, the high association and dissociation rates, and the heterogeneity of binding sites so frequently found with pharmacological and biochemical ligand-receptor interactions. Furthermore, the measured apparent association constant is a function of the whole system rather than just the receptor. The same, fully functional receptor may show different binding characteristics in different surroundings, such as in another tissue or in a reconstituted system.

Adrenocorticotropic Hormone↗
PubMed1985

Preferred conformation, orientation, and accumulation of dynorphin A-(1-13)-tridecapeptide on the surface of neutral lipid membranes.

Infrared attenuated total reflection (IR-ATR) spectroscopy and capacitance minimization (CM) were used to study the secondary structure, orientation, and accumulation of dynorphin A-(1-13)-tridecapeptide (dynorphin1-13) molecules on the surface of planar membranes prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. The peptide assumed a helical structure oriented perpendicularly on the membrane surface. Binding from aqueous solutions containing 10 mM KCl saturated reversibly at about a bilayer area of 110 nm2 per peptide molecule, an apparent dissociation constant of 11 microM, and rate constants of 2 X 10(2) s-1 (adsorption) and 2 X 10(-3) s-1 (desorption). The results complement those obtained by vesicle-mediated hydrophobic labeling [Gysin, B., & Schwyzer, R. (1983) Arch. Biochem. Biophys. 225, 467-474]. They indicate that the behavior of this amphiphilic peptide in contact with neutral lipid membranes may be quite different from that in molecularly disperse or micellar solutions of detergents or lysolecithins and that, in the case of dynorphin1-13, primary amphiphilicity overrules secondary amphiphilicity.

Dynorphins↗
PubMed1984

Interaction of adrenocorticotropin-(11-24)-tetradecapeptide with neutral lipid membranes revealed by infrared attenuated total reflection spectroscopy.

Infrared attenuated total reflection spectroscopy (IR-ATR) revealed that the hydrophilic adrenocorticotropin-(11-24)-tetradecapeptide ( ACTH11 -24, net charge 6+) assumed an irregular secondary structure when incorporated into the aqueous layers between equilibrated multibilayers of planar membranes prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine ( POPC ). This structure was characterized by a perpendicular orientation of the peptide bonds on the bilayer surfaces, as observed earlier for the corresponding segment of adrenocorticotropin-(1-24)-tetracosapeptide (ACTH1-24, 6+). Once incorporated, ACTH11 -24 was not removed by washing, in agreement with its strong positive charge. In contrast to ACTH1-24, ACTH11 -24 was not measurably adsorbed to the neutral membranes from 0.1 mM aqueous solutions. The more hydrophobic adrenocorticotropin-(1-10)-decapeptide is also not adsorbed. We therefore concluded that adsorption of ACTH1-24 to neutral membranes was dependent on its amphiphilic primary (amphipathic primary) structure that resulted from the covalent combination of the hydrophobic ACTH1-10 segment with the hydrophilic ACTH11 -24 segment. This conclusion was consistent with the results obtained by vesicle-mediated hydrophobic photolabeling and equilibrium dialysis.

Adrenocorticotropic Hormone↗
PubMed1984

Hydrophobic and electrostatic interactions between adrenocorticotropin-(1-24) -tetracosapeptide and lipid vesicles. Amphiphilic primary structures.

Hydrophobic photolabeling with 3-(trifluoromethyl) -3-(m-[125I]iodophenyl) diazirine ( [125I]TID [Brunner, J., & Semenza , G. (1981) Biochemistry 20, 7174-7182] ) and equilibrium dialysis were used to study hydrophobic and electrostatic interactions between three adrenocorticotropin fragments and liposomes prepared from mixtures of phosphatidylcholine with phosphatidic acid or phosphatidylserine. Corticotropin-(1-10)-decapeptide (ACTH1-10, net charge 0) formed hydrophobic clusters with [125I]TID in aqueous solutions at peptide concentrations above 1 microM but did not interact appreciably with neutral or anionic liposomes. Corticotropin -(11-24)-tetradecapeptide ( ACTH11 -24, net charge 6+) reacted electrostatically with anionic liposomes but showed no hydrophobic interactions. Corticotropin-(1-24)-tetracosapeptide (ACTH1-24, net charge 6+), a covalent combination of the two fragments, exhibited both hydrophobic and electrostatic interactions with lipid vesicles. Edman degradation and chymotryptic hydrolysis of labeled ACTH1-24 revealed that the hydrophobic interaction involved the N-terminal decapeptide "message" segment (corresponding to ACTH1-10) which entered the membrane and that the electrostatic interaction was caused by the C-terminal tetradecapeptide "address" segment (corresponding to ACTH11 -24) which remained on the aqueous membrane surface. This surface is in complete analogy to that reported for dynorphin- (1-13)-tridecapeptide by Gysin and Schwyzer [ Gysin , B., & Schwyer , R. (1983) FEBS Lett. 158, 12-16; Gysin , B., & Schwyzer , R. (1983) Arch. Biochem. Biophys. 225, 467-474]: in both cases, the specific, hydrophobic membrane interaction of the "message" critically depended on the presence of the hydrophilic "address". The results reported here were consistent with those obtained by infrared attenuated total reflection spectroscopy [ Gremlich , H.-U., Fringeli , U.-P., & Schwyzer , R. (1983) Biochemistry 22, 4257-4263] and were crucial for their interpretation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1983

Conformational changes of adrenocorticotropin peptides upon interaction with lipid membranes revealed by infrared attenuated total reflection spectroscopy.

Infrared attenuated total reflection (IR-ATR) spectroscopy was used to study conformational and topological aspects of the interaction between two adrenocorticotropin fragments and dioleoylphosphatidylcholine membranes. Corticotropin-(1-10)-decapeptide, ACTH1-10, was found to exist as a rigid antiparallel pleated sheet structure in dry membranes. In aqueous environment, it completely escaped from the lipid. This dominant preference for the aqueous phase is a possible explanation for the very low biological potency of ACTH1-10 in some assays. On the other hand, the very potent corticotropin-(1-24)-tetracosapeptide, ACTH1-24, was firmly incorporated into dry and wet membranes. Aqueous environment even promoted the peptide-lipid interaction. Under these latter conditions, part of the molecule entered the bilayer and adopted a helical structure with the axis oriented perpendicularly to the bilayer plane. Contact of a 0.1 mM solution of ACTH1-24 in liquid deuterium oxide with the pure lipid membrane system resulted in measurable adsorption of the peptide to the membrane with the same conformational and topological characteristics as described above (perpendicularly oriented helix entering the bilayer). The helical part of the ACTH1-24 molecule entering the bilayer was the quite hydrophobic N-terminal decapeptide unit ("message" segment). The adjacent hydrophilic C-terminal tetradecapeptide unit ("address" segment) remained on the membrane surface. As the message region is essential for triggering corticotropin receptors, its intrusion into the membrane and its adoption of an oriented, helical conformation may facilitate receptor stimulation.

Adrenocorticotropic Hormone↗
PubMed1983

Liposome-mediated labeling of adrenocorticotropin fragments parallels their biological activity.

To test our hypothesis that specific interactions of ACTH peptides with model lipid membranes reflect the biological importance of similar interactions on target cells, we investigated the liposome-mediated labeling of ACTH fragments with the extremely hydrophobic photolabel, 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine. Correlations were found between the labeling rates and the agonistic and antagonistic potencies of the peptides for in vitro steroidogenesis and inhibition of a synaptosomal protein kinase. A model for the cross-reactivity between ACTH and opioid peptides is discussed.

Adrenal Cortex Hormones↗
PubMed1983

Head group and structure specific interactions of enkephalins and dynorphin with liposomes: investigation by hydrophobic photolabeling.

The interaction of the opioid enkephalins and endorphins with lipid bilayers is largely unknown. Such interactions might, however, be important for understanding the molecular mechanisms of biological action. We have therefore studied the interaction of several enkephalins and of dynorphin-(1-13)-tridecapeptide (dynorphin1-13) with model membrane systems, using the extremely hydrophobic photolabel of J. Brunner and G. Semenza, (Biochemistry 20, 7174-7182 (1981)) 3-trifluoromethyl-3-(m[125I]iodophenyl)diazirine. By observing several limitations of the method, it was possible to characterize hydrophobic interactions of opioid peptides with liposomes prepared from egg yolk phosphatidylcholine (PC) plus dipalmitoylphosphatidic acid (PA), from brain phosphatidylserine (PS) alone, and from brain cerebroside sulfate (CS) alone, Dynorphine1-13 exhibited strong hydrophobic interactions through its N-terminal "message" segment which were potentiated by the "address" that itself remained in the aqueous phase. This behavior was consistent with the reported pharmacological potentiation. The enkephalins were generally weakly labeled in the PC/PA and PS systems. However, in the CS systems the preferentially mu agonists were labeled very strongly whereas the preferentially delta agonists were labeled more weakly yet. The kappa agonist, dynorphin1-13, was strongly, but more equally labeled in the three systems. Thus, there was a head group specificity that, in our series of compounds, correlated with opiate receptor sub-type specificity. The results were consistent with the behavior of the mu agonist, morphine.

Amino Acid Sequence↗
PubMed1982

Interaction of p-nitrophenylalanine enkephalins with mu-, delta- and kappa-subtypes of the opiate receptor.

Substitution of L-p-nitrophenylalanine for phenylalanine in position 4 of [D-Ala2, KLeu-NH2(5)]enkephalin analogues increased their affinity for mu-, delta- and kappa-binding sites in guinea-pig brain, increased their potency to inhibit electrically evoked contractions of the guinea-pig ileum and mouse vas deferens, and increased their analgesic potency in the mouse tail flick test, Introduction of L-adamantylalanine, but not of L-neopentylglycine, in position 5 resulted in a loss of activity.

Animals↗
PubMed1982

Peptides and the new endocrinology.

The discovery of regulatory peptides common to the nervous and the endocrine systems (brain, gut, and skin) has brought about a revolution in our concepts of endocrinology and neurology. We are beginning to understand some of the complex interrelationships between soma and psyche that might, someday, be important for an integrated treatment of diseases. Examples of the actions of certain peptides in the periphery and in the central nervous system are given, and their biosynthesis and molecular anatomy as carriers for information are discussed.

Adrenocorticotropic Hormone↗
PubMed1981

Superpotency and superaffinity phenomena in the stimulation of steroidogenesis in adrenocortical cells by adrenocorticotropin-tobacco mosaic virus conjugates.

Adrenocorticotropin-(1-24)-tetracosapeptide was covalently attached to tobacco mosaic virus in two different manners: (i) through a handle near the C-terminus on tyrosine-(23) and (ii) through a handle at the N-terminus on serine-(1). Compounds of type (i) with their N-terminal message sequence freely exposed on the virion surface were considerably more potent for stimulating steroidogenesis in isolated adrenocortical cells than those of type (ii) with a more congested message. Conjugates with 50 or less hormone molecules per virion were less potent per peptide unit than the "free" handle-substituted hormones, whereas conjugates with 150 ACTH units exhibited superpotency effects. Superpotency disappeared when the substituted virions were disaggregated into (substituted) capsomers, suggesting influences of hormone clustering and virion geometry on biological activity. Superpotent stimulation was irreversible under conditions that immediately inhibited steroidogenesis by ACTH (dilution, addition of a peptide antagonist). Thus, superpotency might be caused by superaffinity arising from a slow rate of dissociation of the conjugates from the target cell receptors. The reason for the slow dissociation rate is still unclear: possible explanations include cooperative affinity, rapid internalization of the conjugate-receptor complexes, or decreased rates of peptide degradation at the receptor site.

Adrenal Cortex↗
PubMed1981

Tobacco mosaic virus-enkephalin conjugates: potentiation of opioid activity.

Covalent tobacco mosaic virus-enkephalin analogue conjugates containing between 5 and 450 agonist molecules attached through their C-terminal amino acids were prepared and assayed in pharmacological and binding assays that distinguish between mu- and delta-receptors. Increases in peptide- and receptor-specific potency and affinity were observed with a certain preference of mu- over delta-receptors. The results may become important for mapping receptors or for isolating opiate receptor-bearing membrane vesicles.

Animals↗
PubMed1981

Electronic, steric, and hydrophobic factors influencing the action of enkephalin-like peptides on opiate receptors.

The requirements of opiate receptors for electronic, steric, and hydrophobic properties of the amino acids in Pos. 4 and 5 of enkephalin-like peptides were studied. A series of [D-Ala2]-enkephalins containing carboranylalanine, adamantylalanine, t-butylglycine and p-nitrophenylalanine were synthesized and their pharmacological activities in the guinea pig ileum and their naloxone displacement in rat brain homogenates determined. An electronegative (-E) aromatic character of the amino acid in Pos. 4 strongly enhanced potency, overruling steric effects. The enhancement was not caused by exceptional enzyme resistance. Amino acid in Pos. 5 contributed to potency mainly through its effect on overall hydrophobicity. The two C-terminal amino acids seem to function as potentiator and address elements in the enkephalins.

Animals↗
PubMed1980

Structure and function in neuropeptides.

This report reviews some aspects of the organization of molecular information, structure-activity relations and receptor interactions of three members of a family of neuroactive and hormonal peptides, adrenocorticotrophin (ACTH), alpha-melanotrophin (alpha-MSH) and the enkephalins, as they are presently being investigated in the author's laboratory (in collaboration with H. W. Kosterlitz, D. Schulster and P. W. Schiller). It has been established that ACTH acts on two different steroidogenically responsive receptors in rat adrenocortical cells: one that stimulates steroidogenesis without cyclic AMP synthesis and one that induces cyclic AMP production. This finding is a further example of the pleiotropic action of the opiocortin gene through different mechanisms. Another recent discovery, also related to the organization of ACTH information, reveals an unexpected interaction of ACTH(1-24) with lipid bilayer membranes: the molecule binds to the membranes in a reversible fashion and penetrates them. Parts of the hormonal message are exposed on the side of the membrane opposite to that to which the hormone was added. New 'fat' amino acids like carboranylalanine and adamantylalanine, as well as t-butylglycine, have been used to establish structure-activity relations and the influence of strongly enhanced lipophilicity on the biological activity of the enkephalins. An address/potentiator function of the two C-terminal amino acids is suggested. Tobacco mosaic virus (TMV) has been used as a carrier for covalently attached peptide hormones. Attachment of large numbers of hormone molecules endows these conjugates with the properties of superpotency, superaffinity and prolonged action on the target cell. Some of these properties are illustrated by TMV-enkephalin conjugates.

Adrenocorticotropic Hormone↗