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See detailConformally Equivariant Quantization - a Complete Classification
Michel, Jean-Philippe ULiege

in Symmetry, Integrability and Geometry: Methods and Applications [=SIGMA] (2012), 8(022), 20

Conformally equivariant quantization is a peculiar map between symbols of real weight d and differential operators acting on tensor densities, whose real weights are designed by l and l+d. The existence ... [more ▼]

Conformally equivariant quantization is a peculiar map between symbols of real weight d and differential operators acting on tensor densities, whose real weights are designed by l and l+d. The existence and uniqueness of such a map has been proved by Duval, Lecomte and Ovsienko for a generic weight d. Later, Silhan has determined the critical values of d for which unique existence is lost, and conjectured that for those values of d existence is lost for a generic weight l. We fully determine the cases of existence and uniqueness of the conformally equivariant quantization in terms of the values of d and l. Namely, (i) unique existence is lost if and only if there is a nontrivial conformally invariant differential operator on the space of symbols of weight d, and (ii) in that case the conformally equivariant quantization exists only for a finite number of l, corresponding to nontrivial conformally invariant differential operators on l-densities. The assertion (i) is proved in the more general context of IFFT (or AHS) equivariant quantization. [less ▲]

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See detailConformance relation, associated equivalence, and minimum canonical tester in LOTOS
Leduc, Guy ULiege

in Jonsson, B.; Parrow, J.; Pehrson, B. (Eds.) Protocol Specification, Testing, and Verification, XI (1991, June)

We first study the conf relation proposed by E. Brinksma and G. Scollo to formalise testing conformance. It is well-known from their work that, in order to test whether an implementation of a ... [more ▼]

We first study the conf relation proposed by E. Brinksma and G. Scollo to formalise testing conformance. It is well-known from their work that, in order to test whether an implementation of a specification S (i.e. I conf S), it suffices to build, from S, a canonical tester T(S) such that, when T(S) is synchronised with an implementation I, it always reaches a correct final state if, and only if, I conf S. For instance, if I is not a valid implementation of S, the canonical tester T(S) may deadlock with I before reaching a correct final state. We put into evidence the role of the equivalence relation, conf-eq, associated naturally with conf. An important result states that if S1 conf S2, their canonical testers T1 and T2 must also satisfy T1 conf-eq T2, and reversely. Therefore, the best approach is to define the canonical tester modulo conf-eq, whereas it is currently defined modulo the testing equivalence te. Taking into account that conf-eq is weaker than te, we were able to propose a minimum canonical tester which is simpler than T(S): unlike T(S), it may have fewer traces than the specification S. The term minimum means that no trace from this tester can be deleted without losing the exhaustive test property or, stated otherwise, without taking the risk of accepting an invalid implementation (in the conf sense). [less ▲]

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See detailLa conformation bouchère des agneaux. Etude d'après la variabilité génétique entre races
Laville, E.; Bouix, J.; Sayd, T. et al

in INRA Productions Animales (2002), 15(1), 53-66

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See detailConformation of Homopolypeptides Studied by Single Molecule Force Spectroscopy
Willet, N.; Lecommandoux, S; Hinterdorfer, P et al

Conference (2010, May 25)

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See detailConformational analyses of bacillomycin D, a natural antimicrobial lipopeptide, alone or in interaction with lipid monolayers at the air-water interface
Nasir, Mehmet Nail ULiege; Besson, Françoise

in Journal of Colloid & Interface Science (2012), 387(1), 187-193

Bacillomycin D is a natural antimicrobial lipopeptide belonging to the iturin family. It is produced by Bacillus subtilis strains. Bacillomycin D is characterized by its strong antifungal and hemolytic ... [more ▼]

Bacillomycin D is a natural antimicrobial lipopeptide belonging to the iturin family. It is produced by Bacillus subtilis strains. Bacillomycin D is characterized by its strong antifungal and hemolytic properties, due to its interaction with the plasma membrane of sensitive cells. Until now, only few limited analyses were conducted to understand the biological activities of bacillomycin D at the molecular level. Our purpose was to analyze the conformation of bacillomycin D using IR spectroscopy and to model its interactions with cytoplasmic membranes using Langmuir interfacial monolayers. Our findings indicate that bacillomycin D contains turns and allow to model its three-dimensional structure. Bacillomycin D formed a monolayer film at the air–water interface and kept its turn conformation, as shown by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To identify the membrane lipid target of bacillomycin D, its interactions with pure lipid monolayers were analyzed and an original behavior of the lipopeptide toward cholesterol-containing monolayers was shown. This original behavior was lost when bacillomycin D was interacting with pure cholesteryl acetate monolayers, suggesting the involvement of the alcohol group of cholesterol in the lipopeptide–cholesterol interaction. [less ▲]

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See detailConformational analysis of a linear antibiotic heptapeptide using computer graphics
Demeuse, Françoise; De Coen, Jean-Louis; Wathelet, Bernard ULiege

Poster (1991)

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See detailConformational analysis of new 5-HT1A ligands by molecular modeling
Dilly, Sébastien ULiege; Graulich, Amaury; Liégeois, Jean-François ULiege

Conference (2009, May 14)

5-HT1A receptors represent a major target for research and drug development due to their involvement in pathologies such as anxiety,1 depression,2 sleep and memory disorders,3,4 and schizophrenia.5 The ... [more ▼]

5-HT1A receptors represent a major target for research and drug development due to their involvement in pathologies such as anxiety,1 depression,2 sleep and memory disorders,3,4 and schizophrenia.5 The main feature of many drugs having a 5-HT1A affinity is the presence of arylpiperazine moiety.6 Indeed, the protonated nitrogen and the aromatic ring of the arylpiperazine compounds are considered crucial for the interaction with the receptor.7 Interestingly, an in vitro binding study realized in our laboratory reveals the presence of the 1,2,3,6-tetrahydropyridine instead of the piperazine moiety in 4-arylpiperazine-ethyl carboxamide derivatives is highly favourable for 5-HT1A affinity. In order to better understand the favourable effect of this chemical modification, we have performed a conformational analysis of these compounds mainly based on the position of the phenyl ring relative to the piperazine and tetrahydropyridine ones. In the piperazine compounds, the phenyl ring is found in a perpendicular orientation, whereas an almost planar orientation seems to be the most favourable conformation for the tetrahydropyridine compounds (See figure). Therefore, the almost planar orientation of the 4-substituted phenyl ring appears as an important spatial requirement for an optimal interaction with the receptor binding site. This finding could lead to new ideas in the design of high-affinity 5-HT1A ligands. [less ▲]

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See detailConformational Analysis Of Non-Sulfonylurea Hypoglycemic Agents Of The Meglitinide Family
Lins, Laurence ULiege; Brasseur, Robert ULiege; Malaisse, Wj.

in Biochemical Pharmacology (1995), 50(11), 1879-84

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See detailConformational analysis of peptide substrates and inhibitors of the Zn2+ G and serine R61 D-alanyl-D-alanine peptidases
De Coen, Jean-Louis; Lamotte, Josette ULiege; Ghuysen, Jean-Marie ULiege et al

in European Journal of Biochemistry (1981), 121(1), 221-232

The tripeptide Nα,Nɛ-diacetyl-l-lysyl-d-alanyl-d-alanine (Ac2- l-LLys1-dAIa2-dAIa3), which is the standard substrate of the Zn2+ G and serine R61 d-alanyl-d-alanine peptidases, and several ldd tripeptide ... [more ▼]

The tripeptide Nα,Nɛ-diacetyl-l-lysyl-d-alanyl-d-alanine (Ac2- l-LLys1-dAIa2-dAIa3), which is the standard substrate of the Zn2+ G and serine R61 d-alanyl-d-alanine peptidases, and several ldd tripeptide analogues where the size and/or the electrical charge of the side chains at position 1, 2 or 3 have been modified (alterations affecting more than one position at the same time were not investigated) have been submitted to conformational analyses based on both short-range and long-range interactions. Among the many backbone conformers of minimal energy of the øii space that have been characterized, four types of conformers are the most probable ones. Depending on the peptides, these conformers may have varying relative probability P values so that the leader conformer is not always the same, but, in all cases, the sum of their P values is 90% or more. With the Gly1, Gly2 or Gly3 analogues (which encompass a larger conformational space), the above ∑P values are still as high as 35–50%. All the above tripeptides bind to the serine d-alanyl-d-alanine peptidase and with the exception of the Gly3 and Gly2 analogues, to the Zn2+d-alanyl-d-alanine peptidase with virtually the same efficacy, at least within a range of variation of the Km values for the substrates or the Ki values for the inhibitors, which is less than one order of magnitude. Structural variations at position 1, 2 or 3 in the peptides that are compatible with efficient binding are not necessarily compatible with substrate activity, thus converting the modified peptides into competitive inhibitors. In particular, substrate activity requires a long side chain at position 1 in the peptides. Conformational analyses of Ac2-lLys-dAla-dAla show that the main backbone has a tendency to adopt a ring-like shape from which the lLYS side chain protrudes as an extended structure. This latter structure forms with the C-terminal d-alanyl-d-alanine an angle varying between 120° and 180° (depending on the conformers) so that its N-terminal acetyl group is about 1–1.5 nm apart from the scissile amide bond. High turnover numbers (at enzyme saturation) also require a dAla at position 2 with both d-alanyl-d-alanine peptidases and at position 3 in the case of the serine d-alanyl-d-alanine peptidase. Finally, all the conformers of the lAla2 and lAla3 analogues of Ac2-lLys-dAla-dAla fall outside the backbone conformational space that comprises the φiφi angles exhibited by the four types of conformers of the ldd tripeptides. The lAla2 and lAla3 tripeptide analogues do not bind to the serine d-alanyl-d-alanine peptidase (at least at a 10 mM concentration) but they behave as noncompetitive inhibitors of the Zn2+d-alanyl-d-alanine peptidase. [less ▲]

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See detailConformational analysis of surfactins at interfaces
Deleu, Magali ULiege; Gallet, Xavier; Dufrêne, Yves et al

Poster (2000)

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See detailConformational analysis of the calcium--A23187 complex at a lipid--water interface.
Brasseur, Robert ULiege; Deleers, M.; Malaisse, W. J. et al

in Proceedings of the National Academy of Sciences of the United States of America (1982), 79(9), 2895-7

A possible conformation of the complex formed by one calcium ion and two molecules of the ionophore A23187 at a simulated lipid--water interface was predicted by a variant method for conformational ... [more ▼]

A possible conformation of the complex formed by one calcium ion and two molecules of the ionophore A23187 at a simulated lipid--water interface was predicted by a variant method for conformational analysis. This method takes into account, in addition to the Van der Waals energy, electrostatic interaction, and torsional potential, the alteration of electrostatic forces attributable to changes in dielectric constant at the interface and the transfer energy for each part of the complex as it moves through the lipid-water interface. The most probable conformer was characterized by a two-fold axial symmetry that was maintained during transition to the hydrophobic bulk conformation. Minor changes in the interfacial structure were sufficient to achieve the configuration characteristic of the hydrophobic bulk phase. [less ▲]

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See detailConformational analysis of the calcium-antagonist gallopamil.
Brasseur, Robert ULiege; Deleers, M.; Malaisse, W. J.

in Biochemical Pharmacology (1983), 32(3), 437-40

Conformational analysis of gallopamil was performed in order to gain insight into the molecular determinant of its calcium-antagonistic property. Whereas the neutral form of gallopamil was characterized ... [more ▼]

Conformational analysis of gallopamil was performed in order to gain insight into the molecular determinant of its calcium-antagonistic property. Whereas the neutral form of gallopamil was characterized by a single, largely predominant configuration, the protonated form of the drugs yielded several conformers, some of which were characterized by a readily accessible ionized site. The capacity of gallopamil to inhibit ionophore-mediated calcium translocation in a two-phase bulk system was inversely related to the pH of the aqueous phase. These findings indicate that the capacity of gallopamil to interfere with the transport of cations is critically dependent on the availability of a protonated configuration of the drug. [less ▲]

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See detailConformational analysis of β and γ-lactam antibiotics
Lamotte, Josette ULiege; Dive, Georges ULiege; Ghuysen, Jean-Marie ULiege

in European Journal of Medicinal Chemistry (1991), 26(1), 43-50

Geometry optimization, superimposition searches and conformational analysis carried on several lactam antibiotics show that reactivity with the active-site serine penicillin-binding proteins is related to ... [more ▼]

Geometry optimization, superimposition searches and conformational analysis carried on several lactam antibiotics show that reactivity with the active-site serine penicillin-binding proteins is related to a particular spatial disposition of 2 flanking functional groups - namely a C = O or C-OH on 1 side and a carboxylate on the other - with respect to the central scissile amide bond. Such a binding entity is found in one of the most stable conformers of the tripeptide diacetyl-L-Lys-D-Ala-D-Ala conferring substrate activity, and in benzylpenicillin, cephapyrin, thienamycin, gamma-lactam, the 6-spiro-epoxypenicillin S and in one epimer of lactivicin, conferring inactivating potency. This binding entity generates a particular electronic distribution and the fact that it is conserved in compounds belonging to very different chemical families strongly suggests that it is an important feature required for enzyme recognition. [less ▲]

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See detailConformational and interfacial analyses of K3A18K3 and alamethicin in model membranes.
Kouzayha, Achraf; Nasir, Mehmet Nail ULiege; Buchet, René et al

in Journal of Physical Chemistry B (2009), 113

The involvement of membrane-bound peptides and the influence of protein conformations in several neurodegenerative diseases lead us to analyze the interactions of model peptides with artificial membranes ... [more ▼]

The involvement of membrane-bound peptides and the influence of protein conformations in several neurodegenerative diseases lead us to analyze the interactions of model peptides with artificial membranes. Two model peptides were selected. The first one, an alanine-rich peptide, K3A18K3, was shown to be in R-helix structures in TFE, a membrane environment-mimicking solvent, while it was mostly -sheeted in aqueous buffer as revealed by infrared spectroscopy. The other, alamethicin, a natural peptide, was in a stable R-helix structure. To determine the role of the peptide conformation on the nature of its interactions with lipids, we compared the structure and topology of the conformational-labile peptide K3A18K3 and of the R-helix rigid alamethicin in both aqueous and phospholipid environments (Langmuir monolayers and multilamellar vesicles). K3A18K3 at the air-water interface showed a pressure-dependent orientation of its -sheets, while the R-helix axis of alamethicin was always parallel to the interface, as probed by polarization modulation infrared reflection absorption spectroscopy. The -sheeted K3A18K3 peptide was uniformly distributed into DPPC condensed domains, while the helical-alamethicin insertion distorted the DPPC condensed domains, as evidenced by Brewster angle microscopy imaging of the air/interface. The -sheeted K3A18K3 interacted with DMPC multilamellar vesicles via hydrophilic interactions with polar heads and the helical-alamethicin via hydrophobic interactions with alkyl chains, as shown by infrared spectroscopy and solid state NMR. Our findings are consistent with the prevailing assumption that the conformation of the peptide predetermines the mode of interaction with lipids. More precisely, helical peptides tend to be inserted via hydrophobic interactions within the hydrophobic region of membranes, while -sheeted peptides are predisposed to interact with polar groups and stay at the surface of lipid layer [less ▲]

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See detailConformational and thermodynamic changes of the repressor/DNA operator complex upon monomerization shed new light an regulation mechanisms of bacterial resistance against beta-lactam antibiotics
Boudet, J.; Duval, V.; Van Melckebeke, H. et al

in Nucleic Acids Research (2007), 35(13), 4384-4395

In absence of beta-lactam antibiotics, Blal and Mecl homodimeric repressors negatively control the expression of genes involved in P-lactam resistance in Bacillus licheniformis and in Staphylococcus ... [more ▼]

In absence of beta-lactam antibiotics, Blal and Mecl homodimeric repressors negatively control the expression of genes involved in P-lactam resistance in Bacillus licheniformis and in Staphylococcus aureus. Subsequently to P-lactam presence, Blal/Mecl is inactivated by a single-point proteolysis that separates its N-terminal DNA-binding domain to its C-terminal domain responsible for its dimerization. Concomitantly to this proteolysis, the truncated repressor acquires a low affinity for its DNA target that explains the expression of the structural gene for resistance. To understand the loss of the high DNA affinity of the truncated repressor, we have determined the different dissociation constants of the system and solved the solution structure of the B. licheniformis monomeric repressor complexed to the semi-operating sequence OP1, of blaP (1/20P(1)blaP) by using a de novo docking approach based on inter-molecular nuclear Overhauser effects and chemical-shift differences measured on each macromolecular partner. Although the N-terminal domain of the repressor is not subject to internal structural rearrangements upon DNA binding, the molecules adopt a tertiary conformation different from the crystallographic operator-repressor dimer complex, leading to a 300 rotation of the monomer with respect to a central axis extended across the DNA. These results open new insights for the repression and induction mechanisms of bacterial resistance to beta-lactams. [less ▲]

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See detailConformational properties of helical foldamers under force
Willet, Nicolas ULiege; Hinterdorfer, Peter; Lecommandoux, Sébastien et al

Conference (2015, February)

The aim of this study is to investigate the mechanochemical behavior of foldamers able to change their conformation is a stimuli-responsive way. Peptidic secondary structures were studied in detail by ... [more ▼]

The aim of this study is to investigate the mechanochemical behavior of foldamers able to change their conformation is a stimuli-responsive way. Peptidic secondary structures were studied in detail by atomic force microscopy (AFM) at the single-molecule level. Synthetic copolymers containing a polypeptide block were prepared by N-carboxyanhydride amino acid ring-opening polymerization. The polymer chains were grafted onto gold surfaces and their mechanochemical behavior was then studied by AFM single-molecule force spectroscopy (SMFS). The investigated polypeptide blocks were based on polyglutamate, which undergoes transitions from alpha-helix to random coil. This can be induced by external stimuli (pH, ionic strength, temperature) or simply by applying a force. The mechanically driven unfolding of the helical foldamer was characterized in detail. Stretching the folded peptide resulted in original features in the force-distance traces. Plateaus that are specific for the helical conformation were detected, quantified and discussed. Pulling-relaxing SMFS experiments were performed and led to a better understanding of the mechanically induced unfolding of an alpha-helix as a reversible phenomenon. [less ▲]

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See detailConformational-Analysis Of The Calcium Complexes Formed By Meglitinide Analogs
Lins, Laurence ULiege; Brasseur, Robert ULiege; Malaisse, Wj.

in Research Communications In Molecular Pathology and Pharmacology (1995), 90(1), 153-64

The conformation of calcium complexes formed with meglitinide and its hypoglycemic analogs KAD-1229, A-4166, S 3075 and repaglinide was analyzed by a semi-empirical procedure, which includes calculation ... [more ▼]

The conformation of calcium complexes formed with meglitinide and its hypoglycemic analogs KAD-1229, A-4166, S 3075 and repaglinide was analyzed by a semi-empirical procedure, which includes calculation of the molecular hydrophobicity potential. The calcium complexes formed with KAD-1229, A-4166, repaglinide or its enantiomer, displayed favourable attributes to act as ionophores. Such was not the case for the poorly efficient insulinotropic agent meglitinide and the biologically inactive enantiomer of A-4166. The configuration of the calcium complex formed with S 3075 also failed to display the features required for a high ionophoretic capacity. [less ▲]

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