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M Marraud

Publications and source records attributed to M Marraud.

At least 55 records · Page 3Linked to original sources
PubMed1991

Electron distributions in peptides and related molecules. 1. An experimental and theoretical study of N-acetyl-L-tryptophan methylamide.

The thermal vibrations and electron density of N-Ac-L-Trp-NHMe have been analyzed using single-crystal X-ray diffraction data measured at 103 K with Mo K alpha radiation to a resolution corresponding to (sin theta max)/ lambda = 1.17 A-1. Measurements of 10,527 reflections gave 4913 unique data [R(int)(magnitude of F2) = 0.019] of which 2641 had I greater than 3 sigma (I). A multipolar atomic density model was fitted [R(magnitude of F) = 0.028] in order to calculate phases for the crystal structure factors and map the valence-electron distribution. The phase problem for determining deformation densities by Fourier synthesis for noncentrosymmetric crystals is discussed. The experimental density agrees well with the theoretical density from an ab initio SCF molecular wave function calculated at the crystallographic molecular geometry with a split-valence basis set. Both the experimental and theoretical analyses confirm that the electron distribution is the same in the two different peptide groups in the molecule. Crystal data: C14H17N3O2, Mr = 259.31, orthorhombic, P2(1)2(1)2(1), Z = 4, F(000) = 522 e from 295 to 103 K; at 295 K, a = 8.152(2), b = 11.170 (2), c = 15.068 (3) A, V = 1372 A3, Dx = 1.26 mg mm-3; at 103 K, a = 8.209 (3), b = 11.016 (2), c = 14.760 (4) A, V = 1135 A3, Dx = 1.29 mg mm-3, mu = 0.083 mm-1 for lambda = 0.7107 A.

Chemical Phenomena↗
PubMed1991

Two-dimensional 1H-NMR study of antigen-antibody interactions: binding of synthetic decapeptides to an anti-acetylcholine receptor monoclonal antibody.

Two-dimensional NMR experiments [correlated spectroscopy (COSY) and two-dimensional transferred nuclear Overhauser enhancement spectroscopy (TR-NOESY)] have been applied to study the interactions of a monoclonal antibody (mAb) directed to the main immunogenic region (MIR) of the acetylcholine receptor (AChR), and four synthetic decapeptides from the MIR. The decapeptides were the Torpedo AChR alpha 67-76 fragment (W67-N68-P69-A70-D71-Y72-G73-+ ++G74-I75-K76) and its three [A69], [A73], and [A76] analogues. The results led to the following conclusions: (1) the magnitude of the TR-NOE cross peaks does not depend only on the structuration of the peptide in the bound state, but also on restrictions of the mobility, i.e., on the correlation time tau c, which can be different for every residue; (2) the binding capacity of the synthetic peptides to mAbs measured by radioimmunoassay is directly correlated to the NOE magnitude; and (3) the combined interpretation of the COSY and TR-NOESY experiments gives a qualitative information about the nature and the overall conformation of the sequence which is in contact with the mAb binding site.

Amino Acid Sequence↗
PubMed1991

X-ray conformational study of hydrazino peptide analogues.

We have solved the crystal structures of nine pseudo-peptide analogues deriving from the hydrazino analogue of glycine or valine (N beta H2-N alpha H-C alpha HR-CO2H, R = H or iPr) or proline (N beta H2-N alpha-C alpha H-CO2H) and containing the hydrazide (CO-N beta H-N alpha less than) or N beta-Z-aminoamide [formula; see text] [CO-N alpha(N beta HZ)] peptidomimetic link. This study gives access to the average geometry of these two links, to their inter- and intramolecular interaction modes, and to their influence on the conformational properties of the molecules.

Amino Acid Sequence↗
PubMed1991

The main immunogenic region (MIR) of the nicotinic acetylcholine receptor and the anti-MIR antibodies.

Myasthenia gravis (MG) is caused by autoantibodies against the nicotinic acetylcholine receptor (AChR) of the neuromuscular junction. The anti-AChR antibodies are heterogeneous. However, a small region on the extracellular part of the AChR alpha subunit, called the main immunogenic region (MIR), seems to be the major target of the anti-AChR antibodies, but not of the specific T-cells, in experimental animals and possibly in MG patients. The major loop of the overlapping epitopes for all testable anti-MIR monoclonal antibodies (MAbs) was localized within residues 67-76 (WNPADYGGIK for Torpedo and WNPDDYGGVK for human AChR) of the alpha subunit. The N-terminal half of alpha 67-76 is the most critical, Asn68 and Asp71 being indispensable for binding. Yet anti-MIR antibodies are functionally and structurally quite heterogeneous. Anti-MIR MAbs do not affect channel gating, but they are very potent in mediating acceleration of AChR degradation (antigenic modulation) in cell cultures and in transferring experimental MG in animals. Fab fragments of anti-MIR MAbs bound to the AChR prevent the majority of the MG patients' antibodies from binding to and causing loss of the AChR. Whether this inhibition means that most MG antibodies bind on the same small region or is a result of broad steric/allosteric effects is under current investigation.

Adult↗
PubMed1991

Changes in the c.d. spectra of calf thymus DNA induced by sequential polypeptides in aqueous solutions. Part I.

Interactions of calf thymus DNA with sequential polypeptides were studied using c.d. spectroscopy in aqueous solutions. It was found that DNA structural alterations induced by sequential polypeptides (L-Arg-X-Gly)n (where X = L-Val, Leu, Ile, Nva, Nle) are modulated by the nature of the X residue. Thus, the polypeptide (L-Arg-L-Nva-Gly)n induced the 10.2B-DNA form, whereas the polypeptides (L-Arg-L-Ile-Gly)n having one methyl group less on the X residue side chain, did not provide any significant modification to the structure of DNA. The effect of ionic strength from 0.14 M NaCl (physiological value) to zero was also analysed on the basis of the observed c.d. changes and the degree of complexation in the DNA-polypeptides was estimated.

Amino Acid Sequence↗
PubMed1991

Changes in the c.d. spectra of calf thymus DNA induced by sequential polypeptides in trifluoroethanol solutions. Part II.

Interactions between calf thymus DNA and (L-Arg-X-Gly)n sequential polypeptides (where X = L-Ala, Val, Leu, Ile, Nva, Nle) in trifluoroethanol: water (40:60) solutions in the salt range of 0.12-0.5 M NaCl, were studied using c.d. spectroscopy. It was found that DNA tertiary structure (psi form) is modulated by the nature of the polypeptides (variation of X residue). The effect of the secondary structure of polypeptides on the formation of psi-DNA was also analysed. Unordered polypeptides destabilized psi aggregates, while helical polypeptides favoured DNA tertiary structure. A loss of tertiary structure was observed in the presence of the (L-Arg-L-Val-Gly)n, which can be attributed to the ability of valine to suppress psi-type DNA.

Amino Acid Sequence↗
PubMed1991

Synthesis, crystal structure and molecular conformation of the tBuCO-D,L-Ala-delta Z-Phe-NHiPr alpha,beta-unsaturated dipeptide.

The crystal structure of the tBuCO-D,L-Ala-delta Z-Phe-NHiPr dipeptide has been solved by X-ray diffraction. The peptide crystallizes in monoclinic space group P2(1)/c with a = 13.445 (3) A, b = 35.088 (4) A, c = 14.755 (3) A, beta = 116.73 (1) degree, Z = 12 and dc = 1.151 g.cm-3. The three independent molecules per asymmetric unit accommodate a beta II-folded conformation, but only one of them contains the typical i + 3----i interaction characterizing a beta-turn. In the other two molecules, the N...O distance exceeds 3.2 A, a value generally considered the upper limit for hydrogen bonds in peptides. In solution, the beta II-turn conformation is largely predominant.

Dipeptides↗
PubMed1991

The main immunogenic region of the acetylcholine receptor. Structure and role in myasthenia gravis.

Auto-antibodies to the nicotine acetylcholine receptor (AChR) cause the disease myasthenia gravis (MG). Animals immunized with AChR or receiving anti-AChR antibodies acquire MG symptoms. The majority of the monoclonal antibodies (mAbs) raised in rats against intact AChR bind to a region on the extracellular side of the AChR's alpha-subunit, the main immunogenic region (MIR). The major loop of the overlapping epitopes for several anti-MIR mAbs has been localised between residues 67-76 of the alpha-subunit. Anti-MIR mAbs are very potent in accelerating AChR degradation (antigenic modulation) in muscle cell cultures and transferring experimental MG in animals. Fab fragments of single anti-MIR mAbs when bound to the AChR inhibit two-thirds of the MG patients' antibodies from binding and from inducing antigenic modulation of the AChR. This suggest that the majority of the human MG antibodies are also directed against the MIR. It has however to be verified by direct experiments.

Animals↗
PubMed1990

Antigenic role of single residues within the main immunogenic region of the nicotinic acetylcholine receptor.

The target of most of the autoantibodies against the acetylcholine receptor (AChR) in myasthenic sera is the main immunogenic region (MIR) on the extracellular side of the AChR alpha-subunit. Binding of anti-MIR monoclonal antibodies (mAbs) has been recently localized between residues alpha 67 and alpha 76 of Torpedo californica electric organ (WNPADYGGIK) and human muscle (WNPDDYGGVK) AChR. In order to evaluate the contribution of each residue to the antigenicity of the MIR, we synthesized peptides corresponding to residues alpha 67-76 from Torpedo and human AChRs, together with 13 peptide analogues. Nine of these analogues had one residue of the Torpedo decapeptide replaced by L-alanine, three had a structure which was intermediate between those of the Torpedo and human alpha 67-76 decapeptides, and one had D-alanine in position 73. Binding studies employing six anti-MIR mAbs and all 15 peptides revealed that some residues (Asn68 and Asp71) are indispensable for binding by all mAbs tested, whereas others are important only for binding by some mAbs. Antibody binding was mainly restricted to residues alpha 68-74, the most critical sequence being alpha 68-71. Fish electric organ and human MIR form two distinct groups of strongly overlapping epitopes. Some peptide analogues enhanced mAb binding compared with Torpedo and human peptides, suggesting that the construction of a very antigenic MIR is feasible.

Amino Acid Sequence↗
PubMed1990

17O- and 14N-NMR studies of Leu-enkephalin and enkephalin-related fragments in aqueous solution.

17O- and 14N-nmr chemical shifts and line widths of the carboxyl and amino terminal groups of Leu-enkephalin--Tyr-Gly-Gly-Phe-[17O]Leu-Oh--and enkephalin-related fragments--[17O]Leu-OH, Phe-[17O]Leu-OH, Gly-Phe-[17O]Leu-OH, and Gly-Gly-Phe-[17O]Leu-OH--were measured in aqueous solution over the entire H pH range. Enrichment in 17O was achieved by saponification of the corresponding O-methyl esters. Ionization constants and titration shifts were obtained by nonlinear least-squares fits to one-proton titration curves. [17O]Leu-OH exhibits a profound pH-dependent solvation change on deprotonation of the carboxyl group, as shown by 17O- and 14N-nmr line widths. In contrast, the peptides studied do not exhibit pH-dependent conformational (solvation) changes on deprotonation of the carboxyl group, and a head-to-tail intramolecular association between the ionic terminal groups should be excluded. It is shown that the peptides do not exhibit isotropic overall molecular motion and that segmental motion rather than fast internal motion influences the effective correlation times at the sites of the carboxyl oxygens and the amino nitrogen.

Amino Acid Sequence↗
PubMed1989

17O-NMR studies of the conformational and dynamic properties of enkephalins in aqueous and organic solutions using selectively labeled analogues.

The synthesis of Leu-enkephalin selectively 17O-enriched in Gly2 and Gly3 is reported. The 17O-nmr chemical shifts of [17O-Gly2, Leu5]- and [17O-Gly3, Leu5]-enkephalins in H2O are almost identical and independent of the pH. Since hydrogen bonding is the dominant factor governing the chemical shifts of the peptide oxygen, it can be concluded that the hydration state of both oxygens is identical and independent of the pH. The 17O chemical shifts of the [17O-Leu5]-enkephalin terminal carboxyl group at pH approximately 1.9 and 5.6 are very different in H2O but very similar in CH3CN/DMSO (4:1) solution. This suggests that the protonation state of the carboxyl group at both pH values in CH3CN/DMSO solution is the same and consequently that Leu-enkephalin exists in the neutral form at pH approximately 5.6. In this organic mixed solvent system both Gly2 and Gly3 oxygen resonances exhibit a significant shift to high frequency by the same extent (delta delta approximately 30 ppm). It is concluded that both peptide oxygens are not hydrogen bonded to an appreciable extent and that no specific 2----5 hydrogen bonding exists to an appreciable extent. This conclusion is in agreement with the energy of activation for molecular rotation, as determined from T1 measurements, which was found to be almost identical for both [17O-Gly2, Leu5]- and [17O-Gly3, Leu5]-enkephalins in CH3CN/DMSO (4:1) mixed solvent.

Enkephalins↗
PubMed1989

A crystal molecular conformation of leucine-enkephalin related to the morphine molecule.

Leucine-enkephalin (Try1-Gly2-Gly3-Phe4-Leu5) has been crystallized as a trihydrate from water solution. X-ray diffraction reveals a tightly folded molecular conformation with two fused beta III- (Gly2-Gly3) and beta I- (Gly3-Phe4) turns. The Tyr1 and Phe4 aromatic rings have a close orthogonal arrangement analogous to the tyramine and cyclohexenyl rings in morphine. This suggests that the conformation found in the trihydrate crystal structure could be required for recognition by mu-receptor sites.

Enkephalin, Leucine↗
PubMed1989

Pseudopeptides and beta folding: x-ray structures compared with structures in solution.

In order to restrain the flexibility of the peptide molecules and reduce their biodegradation, modifications of the main chain are now introduced in pseudopeptide analogues. Surprisingly, there is very little data on the conformational properties of these derivatives. We have examined pseudopeptide analogues of RCO-X-Y-NHR' model dipeptides in the depsi, N-methylated, reduced, retro, alpha, beta-dehydro, beta-amino acid, and hydrazino series, in the solid state by x-ray diffraction, and in solution by ir and 1H-nmr spectroscopy. This study provides us with accurate dimensions of the peptide surrogates, and gives some information on the conformational tendencies induced by these substitutions, with reference to those of the related dipeptide sequences.

Dipeptides↗
PubMed1989

Two-dimensional 1H-NMR study of synthetic peptides containing the main immunogenic region of the Torpedo acetylcholine receptor.

A comparative 1H-NMR spectral study of a synthetic decapeptide containing the main immunogenic region of the Torpedo acetylcholine receptor (AChR; WNPADYGGIK, representing the alpha 67-76 fragment of Torpedo AChR) with four analogous peptides (WNP3-D5YGGIK, WNPAA5YGGIK, WNPADYGGA9K, and WNPD4DYGGV9K) has been carried out in dimethyl sulfoxide. One- and two-dimensional nmr experiments [correlated spectroscopy (COSY), relayed COSY, and phase-sensitive nuclear Overhauser enhancement spectroscopy (NOESY)] were performed to obtain complete assignments of the proton resonances. The presence of strong and multiple short- and long-range NOEs, and especially a strong long-range NOE between the two Asn2-C alpha H and Gly7-C alpha H protons, argues in favor of a rigid folded structure in all five cases. Temperature dependence measurements indicate the existence of three intramolecular interactions involving the Asp3, Gly8, and Lys10 amide protons.

Amino Acid Sequence↗
PubMed1989

Conformational perturbations in retro-analogs of the tBuCO-Ala-Gly-NHiPr dipeptide. Crystal structure of the retro-dipeptide with a reversed Ala-Gly amide bond.

The three retro-analogs of the tBuCO-Ala-Gly-NHiPr dipeptide, in which each amide bond had been successively reversed, were studied in solution by 1H-n.m.r. and i.r. spectroscopy with reference to the conformational properties of their parent dipeptide. Reversal of the Ala-Gly amide bond proved to perturb the folding tendency of the backbone less than the inversion of either of the terminal amide bonds. The crystal structure of the retro-peptide containing a reversed Ala-Gly amide bond was also solved by X-ray diffraction and constitutes the first available data for this retro-peptide series. In contrast to the beta II-folded structure of the parent dipeptide, the retro-peptide molecule adopts an open conformation in the crystal.

Dipeptides↗
PubMed1988

NMR study of a lymphocyte differentiating thymic factor. An investigation of the Zn(II)-nonapeptide complexes (thymulin).

Detailed investigations of a serum peptide (less than Glu1-Ala2-Lys3-Ser4-Gln5-Gly6-Gly7-Ser8-++ +Asn9) were carried out by 1H and 13C NMR spectroscopy to elucidate the structure of the complex formed with Zn(II), thymulin, which has been found to be active in vivo. These experiments were performed in dimethyl sulfoxide-d6 solution at different metal:peptide ratios. The results suggest the following conclusions. (i) The Zn(II) complexation corresponds to a fast exchange on the NMR time scale. (ii) The evolution of 1H and 13C NMR chemical shifts indicates the existence of two types of complexes: a 1:2 species associating two peptide molecules and one Zn(II) ion and a complex with 1:1 stoichiometry. The former is predominant for metal:peptide ratios below unity. (iii) In the 1:2 complex, Zn(II) is coordinated by the Ser4-O gamma H and Asn9-CO2- sites, while in the 1:1 complex, Ser8-O gamma H is the third ligand to the Zn(II) ion. The results are compared with those for the [Ala4] and [Ala8] analogues, and those for the complexes of thymulin with other metal ions (Cu2+ and Al3+) in terms of its biological activity. These comparative studies suggested that the 1:1 complex is the only conformation recognized by the antibodies.

Dimethyl Sulfoxide↗