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M Marraud

Publications and source records attributed to M Marraud.

71 records · Page 4Linked to original sources
PubMed1987

Ab initio quantum mechanical calculations of the variation of the 1H and 13C nuclear magnetic shielding constants in proline as a function of the angle psi.

The variation of the nuclear magnetic shielding constant of the different protons and carbons of trans HCO-L-Pro-NH2 with the value of the angle psi is calculated by a non-empirical method for three conformations of the proline ring. The results concerning the CH protons show that the chemical shift of the alpha, beta and gamma endo hydrogens can vary by more than 1 ppm when psi goes from -30 degrees to 180 degrees. The theoretical variation of the chemical shift difference between alpha and gamma or beta and gamma carbons is found to be sensitive to the puckering of the proline ring. For the second of these differences the theoretical results are in agreement with Siemion's relation only for a limited range of molecular conformations. Additional calculations show that the variations of the proton shifts with the value of psi are due to the magnetic anisotropy of the proline carbonyl group and to the polarization of the CH bonds by the multipolar charge distribution carried by this carbonyl. The results are discussed in relation to experiment and the possibility of using 1H and 13C chemical shifts for the determination of the value of the torsion angle about the C alpha C' bond.

Carbon Isotopes↗
PubMed1986

NMR study of thymulin, a lymphocyte differentiating thymic nonapeptide. Conformational states of free peptide in solution.

The nonapeptide less than Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (formerly called serum thymic factor) is a factor produced by the thymic epithelium, which needs a zinc ion to express its immunoregulatory properties. We report here on 1H and 13C NMR investigation of the conformational properties of the free peptide in aqueous medium and in dimethyl sulfoxide-d6 solution by a combination of homo- and heteronuclear one- and two-dimensional experiments. The various resonances have been assigned in a straightforward manner on the basis of 1H,1H COSY spectroscopy for the recognition of the proton spin systems; two-dimensional NOESY spectra with the correlation peaks across amide bonds and for the amino acid sequence assignment; amide bonds and for the amino acid sequence assignment; 13C,1H COSY experiments using selective polarization transfer from 1H- to 13C-nucleus via the 13C,1H long-range couplings for the attribution of the carboxyl and carbonyl groups; and 13C,1H COSY experiments with selective polarization transfer via the 13C,1H direct couplings for the assignment of all the aliphatic carbons. Other experiments such as pH-dependent chemical shifts, combined use of multiple and selective proton-decoupled 1H and 13C NMR spectra, the temperature and the concentration dependence of the proton shifts of the amide resonances, the solvent dependences of peptide carbonyl carbon resonances, and comparison of the spectra with three different analogues were performed. In aqueous solution, the data are compatible with the assumption of a highly mobile dynamic equilibrium among different conformations, whereas in dimethyl sulfoxide-d6, a more rigid structure is found involving three internal hydrogen bonds. These observations provide an insight into the conformational tendencies of this peptidic hormone in two different media.

Dimethyl Sulfoxide↗
PubMed1984

Backbone side chain interactions in peptides. I. Crystal structures of model dipeptides with the Pro-Ser sequence.

The preferential occurrence of amino-acid residues having short polar side-chain within beta-folded regions of crystallized proteins suggests the existence of some stabilizing interaction involving the side polar function. Three model dipeptides tBuCO-L-Pro-L-Ser-NHMe 1, tBuCO-L-Pro-D-Ser-NHMe 2 in the pure enantiomeric a and racemic b forms, and iPrCO-L-Pro-D-Ser-OMe 3 have been investigated in the solid state by X-ray crystallography. Homo and heterochiral sequences 1 and 2 are folded in the beta I and beta II types, respectively, whereas 3 obviously accommodates an open conformation. Besides the i + 3 leads to i hydrogen bond typical of beta-bends in 1, 2a, and 2b, the Ser NH group in all four crystal structures is a proton donor to the lone orbitals of the Ser O gamma oxygen atom. The result is that the disposition of the Ser C alpha--C beta bond corresponds to the rotamer III (chi 1 congruent to 60 degrees). As shown by the crystal structure of 3, the intra-Ser NH. . .O gamma hydrogen bonding is not restricted to beta-folded Pro-Ser sequences. Therefore, this interaction is not only a stabilizing factor for beta-turns but it is also probably responsible for the already mentioned stability of rotamer III for the Ser C alpha--C beta bond in peptides and protein.

Dipeptides↗
PubMed1984

Backbone side chain interactions in peptides. II. Solution study of serine-containing model dipeptides.

The high content of serine in beta-folded regions of proteins may be the consequence of some specific interaction between the peptide backbone and the hydroxyl group of the Ser side-chain. The resolution of the X-ray structures of three peptides with the Pro-Ser sequence protected on both ends by amide and/or ester functions indicates that the Ser NH bond is a proton donating group to the Ser O gamma atom in the solid state. The present study deals with spectroscopic investigations on five Ser-containing model dipeptides with the L-Pro-D-Ser 1, L-Pro-L-Ser 2, L-Ala-L-Ser 3, L-Ser-L-Ala 4 and L-Ser-Gly 5 sequences protected on their N and C-termini by tBuCO and NHMe groups, respectively. The N--H. . .O gamma interaction found in the solid state of 1 and 2 is at least partly retained in solution and its occurrence in X-Ser sequences is fully compatible with beta-folding. The same is not true for Ser-X sequences in which the competition between the typical beta-turn i + 3 leads to i hydrogen bond and the N--H . . . O gamma interaction results in lower contents of beta-folded conformers. Because of this latter interaction, the rotamer III (chi 1 congruent to 60 degrees) is the most frequent disposition of the Ser C alpha--C beta bond in all five derivatives.

Circular Dichroism↗
PubMed1981

N-methyl peptides. III. Solution conformational study and crystal structure of N-pivaloyl-L-prolyl-N-methyl-N'-isopropyl-L-alaninamide.

The study of tBuCO-L-Pro-Me-L-Ala-NHiPr (1) by i.r. and n.m.r spectroscopies has indicated that the middle amide group accommodates preferentially the cis arrangement in inert (CCl4) and aprotic (DMSO) solvents. Cis conformers are folded by a strong intramolecular hydrogen bond involving both terminal CO and NH groups whereas the minor trans conformers accommodate an open conformation. The cis folded form is retained in the solid state and its crystal structure was fully characterized by X-ray diffraction.

Crystallization↗
PubMed1981

N-Methyl peptides. IV. Water and beta-turn in peptides. Crystal structure of N-pivaloyl-L-prolyl-N,N'-dimethyl-D-alaninamide in the anhydrous and monohydrated states.

The model tripeptide tBuCO-L-Pro-Me-D-Ala-MHMe crystallizes in both anhydrous (1) and monohydrated (2) states: 1, monoclinic space group C2 with a = 20.030 (2) A, b = 5.836 (2) A, c = 14.958 (3) A and beta = 94.11 (1) degrees; 2, orthorhombic space group P212121 with a = 6.971 (6) A, b = 11.766 (3) A, and c = 22.394 (8) A. Both crystal structures were solved by X-ray diffraction in order to characterize the influence of water on the molecular structure. The anhydrous molecule accommodates the well-known, beta II-folded conformation with three trans amide functions and an intramolecular i + 3 leads to hydrogen bond. In the hydrated molecule, water is inserted in a loop containing 12 atoms and induces some conformational changes of the peptide backbone.

Dipeptides↗
PubMedDate not supplied

Triphosgene: an efficient carbonylating agent for liquid and solid-phase aza-peptide synthesis. Application to the synthesis of two aza-analogues of the AChR MIR decapeptide.

The N alpha/C alphaH exchange in aza-peptides has the advantage of preserving the side chain. Bis(trichloromethyl)carbonate or triphosgene is a solid, stable phosgene substitute which retains its high reactivity. Temperature and coupling times are greatly reduced with reference to other usually recommended carbonylating agents, while purity and yield are increased. It has been used, in both liquid- and solid-phase procedures, for the synthesis of various aza-analogues of dipeptides, tripeptides and decapeptides containing the alanine, aspartic acid and asparagine aza-residue.

Aza Compounds↗
PubMedDate not supplied

Folded structures in protonated reduced dipeptides.

Reduced dipeptides with the general formula RCO-Xaa-rXbb-N+HR'R" (rXbb, reduced analogue of residue Xbb: NH-C alpha HR1-CrH2) are shown to adopt a folded conformation in solution and in the solid state. The protonated reduced amide bond is an active proton donor capable of interacting with a peptide carbonyl to give a strong hydrogen bond topologically equivalent to the i+2 or i+3-->i interaction. The resulting conformation is similar to the y- or beta-turn structure found in peptides and proteins.

Crystallization↗
PubMedDate not supplied

Production of antibodies to alpha(181-192) peptides of neuronal nicotinic acetylcholine receptor coupled to protein carriers in different orientations.

The antibodies to nicotinic acetylcholine receptor alpha(181-192) synthetic peptides were elicited in rabbits and mice using the peptides conjugated to protein carriers in different orientations, either through C-terminal Cys (S-conjugates), or through amino groups (N-conjugates). S-conjugated peptides were less potent in eliciting peptide-specific antibodies compared to N-conjugates and this type of conjugation resulted in antibodies to the coupling reagent. However, the epitopes present in either S- or N-conjugated peptides appeared to be similar, indicating that amino acid residues, which form the epitope, were located in the middle part of the peptide and did not include both N- and C-terminal residues. Peptide conjugation to a protein carrier did not play a role in stabilizing the peptide conformation, but was necessary to concentrate the peptide epitopes on the carrier surface enabling bivalent antibody binding.

Amino Acid Sequence↗
PubMedDate not supplied

1H-NMR studies on arginine tripeptides: evidence for guanidinium-C-terminal carboxylate interactions.

Guanidinium-C-terminal carboxylate interactions are involved in the establishment of the secondary structure of various biologically active peptide sequences. The conformational properties of a series of arginine-containing tripeptides, L-Arg-X-Gly (X = L-Ala, Val, Leu), in DMSO solutions at physiological pH, have been studied by means of 1D and 2D 1H-NMR spectroscopy. Measurements of the chemical shifts, NOE effects and temperature coefficients showed that the ArgN epsilon H and ArgN eta H2 groups form two hydrogen bonds with the C-terminal carboxylate moiety, whereas the ArgN alpha-terminal nitrogen is in the amino state. Our results point out the significant contribution of the C-terminal carboxylate group, at physiological pH, in the stabilization of the Arg side-chain structure in peptides simultaneously containing arginine residues and carboxy terminal sequences.

Amino Acid Sequence↗
PubMedDate not supplied

2D-NMR and molecular dynamics analysis of the Torpedo californica acetylcholine receptor alpha 67-76 fragment and of its [Ala76]-analogue.

The alpha 67-76 fragment (Trp67-Asn68-Pro69-Ala70-Asp71-Tyr72 -Gly73-Gly74- Ile75-Lys76) of the Torpedo californica acetylcholine receptor (AChR) is selectively recognized by antibodies against the main immunogenic region of the AChR. The antibody binding capacity of its [Ala76]-analogue is usually higher than that of the natural fragment. A conformational analysis of these two decapeptides has been carried out in Me2SO by 2D-NMR and molecular dynamics using the SYBYL and BIOGROMOS programs. The natural sequence presents the most numerous and strongest NOE connectivities and is accordingly less flexible than the [Ala76]-analogue. Due to the flexible orientation of the side chains in both peptides, the NOE backbone side chain and side chain-side chain connectivities have not been introduced as distance constraints in the molecular dynamics calculations. It appeared that the N-terminal heptapeptide in both sequences assumes two very similar folded conformations, whereas the Ala substitution induces conformational flexibility in the C-terminal tripeptide sequence. The most flexible [Ala76]-analogue is the most tightly bound to the monoclonal mAb6 anti-AChR antibody, and the transferred NOEs from the bound to the free peptide in D2O reveal some similarity with the intrinsic NOEs for the free natural sequence in Me2SO, suggesting that the bound conformation of the [Ala76]-analogue could not be very different from that of the free natural fragment.

Animals↗
PubMedDate not supplied

Cyclic lactam analogues containing the main immunogenic region of Torpedo acetylcholine receptor.

The majority of autoantibodies against the nicotinic acetylcholine receptor (AChR) bind to an extracellular region of the AChR's alpha-subunit, named main immunogenic region (MIR), with the sequence W67-N-P-A-DY-G-G-I-K76 for the Torpedo californica electric organ. We report on the synthesis and the biological and 1H-NMR studies of two cyclic MIR compounds--namely, [D71,K76]-MIR-NH2 and Ac-[Orn68,D71,A76]-MIR-NH2. The relatively small chemical shift differences between [D71,K76]-MIR-NH2 and the biologically active [A76]-analogue suggest that both MIR derivatives possess similar conformations. Thus, the observed limited anti-MIR MAb binding capacity of [D71,K76]-MIR-NH2 is attributed to the D71,K76 side-chain blockage, through lactam. Formation of the Orn68,D71 cycle in the Ac-[Orn68,D71,A76]-MIR-NH2 preserves, unchanged, the low antigenicity of the linear Ac-[Orn68,A76]-MIR-NH2, thus confirming the key role of position 68. The low temperature coefficient value of A70-NH and the observed NOE effect between P69-C delta H2 and A70-NH in Ac-[Orn68,D71,A76]-MIR-NH2 argue in favor of a type I beta-turn in the Trp67-Orn-P-A70 sequence. However, the N-terminus beta-folding and the Orn68,D71 cycle appear ineffective for optimal antibody molecular recognition.

Amino Acid Sequence↗
PubMedDate not supplied

Use of sequential oligopeptide carriers (SOCn) in the design of potent Leishmania gp63 immunogenic peptides.

The antigenic sequence Ac-IASRYDQL (gp63-SRYD) of the major surface glycoprotein of Leishmania, gp63, was covalently attached to the Lys-N epsilon H2 groups of a new sequential oligopeptide carrier (SOCn), namely, (Lys-Aib-Gly)n (n = 5.6), in order to obtain potent immunogens and site-specific antibodies. It was shown, using 1H-NMR spectroscopy, that the gp63-SRYD octapeptides bound to the SOCn retain their original structural profile outlined by an ionic interaction between R and D side chains and a type 1 beta-turn involving the QNH-->RCO hydrogen bonding. Also, the gp63-SRYD octapeptides linked to the carrier do not experience conformational restrictions, probably because of the favorable conformation of the SOCn. Immunizations of outbred rabbits with the peptide carriers designed resulted in high-titered antibody response to the gp63-SRYD octapeptide and the gp63 cognate protein. Thus, this chemically defined model may be used for incorporating "protective" Leishmania epitopes and ultimately for the design of a multivalent synthetic vaccine against leishmaniosis.

Animals↗