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Jean Doucet

Publications and source records attributed to Jean Doucet.

16 recordsLinked to original sources
PubMed2006

In vivo formation steps of the hard alpha-keratin intermediate filament along a hair follicle: evidence for structural polymorphism.

Several aspects of the intermediate filaments' molecular architecture remain mysterious despite decades of study. The growth process and the final architecture may depend on the physical, chemical, and biochemical environment. Aiming at clarifying this issue, we have revisited the structure of the human hair follicle by means of X-ray microdiffraction. We conclude that the histology-based growth zones along the follicle are correlated to the fine architecture of the filaments deduced from X-ray microdiffraction. Our analysis reveals the existence of two major polymorph intermediate filament architectures. Just above the bulb, the filaments are characterized by a diameter of 100 Angstroms and a low-density core. The following zone upwards is characterized by the lateral aggregation of the filaments into a compact network of filaments, by a contraction of their diameter (to 75 Angstroms) and by the setting up of a long-range longitudinal ordering. In the upper zone, the small structural change associated with the tissue hardening likely concerns the terminal domains. The architecture of the intermediate filament in the upper zones could be specific to hard alpha-keratin whilst the other architecture found in the lower zone could be representative for intermediate filaments in a different environment.

Adult↗
PubMed2005

A cylinder-shaped double ribbon structure formed by an amyloid hairpin peptide derived from the beta-sheet of murine PrP: an X-ray and molecular dynamics simulation study.

A structural model of the murine PrP small beta-sheet was obtained by synthesizing the RGYMLGSADPNGNQVYYRG peptide comprising the two beta-strands 127-133 and 159-164 linked by a four-residue sequence of high turn propensity. The DPNG turn sequence is a "short circuit" replacing the original protein sequence between the two strands. This 19-residue peptide spontaneously forms very long single fibrils as observed by electron microscopy. The X-ray diffraction patterns of a partially oriented sample reveals an average arrangement of the hairpin peptides into a structure which can be geometrically approximated by an empty-core cylinder. The hairpins are oriented perpendicular to the cylinder axis and a 130 A helix period is observed. Based on X-ray diffraction constraints and on more indirect general protein structure considerations, a precise and consistent fibril model was built. The structure consists of two beta-sheet ribbons wound around a cylinder and assembled into a single fibril with a hairpin orientation perpendicular to the fibril axis. Subsequent implicit and explicit solvent molecular dynamics simulations provided the final structure at atomic resolution and further insights into the stabilizing interactions. Particularly important are the zipper-like network of polar interactions between the edges of the two ribbons, including the partially buried water molecules. The hydrophobic core is not optimally compact explaining the low density of this region seen by X-ray diffraction. The present findings provide also a simple model for further investigating the sequence-stability relationship using a mutational approach with a quasi-independent consideration of the polar and apolar interactions.

Amino Acid Sequence↗
PubMed2005

[Adverse drug reactions in the elderly].

Adverse drug reactions (ADRs) are more frequent and more serious in elderly patients (>65 years). Signs and symptoms of ADRs are varied and sometimes atypical. The culprit drugs are mainly cardiovascular and psychotropic agents, anticoagulants, and nonsteroidal antiinflammatory drugs. Some risk factors for ADRs are inherently due to aging, while others can he corrected. These preventable risk factors are related both to drugs themselves and to the behavior of doctors and patients. Given the major human and economic costs of ADRs in the elderly, a proactive prevention policy is urgently needed. This will involve more specific drug evaluation in the elderly, and better information for healthcare professionals and patients alike.

Aged↗
PubMed2004

The intermediate filament architecture as determined by X-ray diffraction modeling of hard alpha-keratin.

Despite investigation since the 1950s, the molecular architecture of intermediate filaments has not yet been fully elucidated. Reliable information about the longitudinal organization of the molecules within the filaments and about the lateral interfilament packing is now available, which is not the case for the transverse architecture. Interesting results were recently obtained from in vitro microscopy observations and cross-linking of keratin, desmin, and vimentin analyses. The structural features that emerge from these analyses could not be fully representative of the in vivo architecture because intermediate filaments are subject to polymorphism. To bring new light to the transverse intermediate filament architecture, we have analyzed the x-ray scattering equatorial profile of human hair. Its comparison with simulated profiles from atomic models of a real sequence has allowed results to be obtained that are representative of hard alpha-keratin intermediate filaments under in vivo conditions. In short, the alpha-helical coiled coils, which are characteristic of the central rod of intermediate filament dimers, are straight and not supercoiled into oligomers; the radial density across the intermediate filament section is fairly uniform; the coiled coils are probably assembled into tetrameric oligomers, and finally the oligomer positions and orientations are not regularly ordered. These features are discussed in terms of filament self-assembling and structural variability.

Animals↗
PubMed2003

The native-like conformation of Ure2p in fibrils assembled under physiologically relevant conditions switches to an amyloid-like conformation upon heat-treatment of the fibrils.

The [URE3] phenotype in the yeast Saccharomyces cerevisiae is inherited by a prion mechanism involving self-propagating Ure2p aggregates. It is believed that assembly of intact Ure2p into fibrillar polymers that bind Congo Red and show yellow-green birefringence upon staining and are resistant to proteolysis is the consequence of a major change in the conformation of the protein. We recently dissected the assembly process of Ure2p and showed the protein to retain its native alpha-helical structure upon assembly into protein fibrils that are similar to amyloids in that they are straight, bind Congo red and show green-yellow birefringence and have an increased resistance to proteolysis (). Here we further show using specific ligand binding, FTIR spectroscopy and X-ray fiber diffraction that Ure2p fibrils assembled under physiologically relevant conditions are devoid of a cross-beta core. The X-ray fiber diffraction pattern of these fibrils reveals their well-defined axial supramolecular order. By analyzing the effect of heat-treatment on Ure2p fibrils we bring evidences for a large conformational change that occurs within the fibrils with the loss of the ligand binding capacity, decrease of the alpha helicity, the formation of a cross-beta core and the disappearance of the axial supramolecular order. The extent of the conformational change suggests that it is not limited to the N-terminal part of Ure2p polypeptide chain. We show that the heat-treated fibrils that possess a cross-beta core are unable to propagate their structural characteristic while native-like fibrils are. Finally, the potential evolution of native-like fibrils into amyloid fibrils is discussed.

Amyloid↗
PubMed2003

In situ chemical speciation of sulfur in calcitic biominerals and the simple prism concept.

The microstructure and composition of two mollusc shells were investigated using a combination of light microscopy, SEM, EPMA, and XANES. The shells of Pinna and Pinctada are composed of calcite prisms separated by organic walls. The prismatic units of Pinna are monocrystalline, and those of Pinctada are polycrystalline with internal organic radial membranes. High-spatial-resolution XANES maps for the different S species across adjacent prisms show that sulfate is the principal component in both the intraprismatic organic matrices and the outer membranes. Additionally, these maps confirm that the inner structures of the prismatic units are different for both genera. In many ways, the prisms of Pinna and Pinctada are different and invalidate the "simple prism" concept.

Animals↗
PubMed2002

A procedure for refining a coiled coil protein structure using x-ray fiber diffraction and modeling.

We describe a combined use of experimental and simulation techniques to configure side chains in a coiled coil structure. As already demonstrated in a previous work, x-ray diffraction patterns from hard alpha-keratin fibers in the 5.15 A meridian zone reflect the global configuration of the chi(1) dihedral angle of the coiled coil side chains. Molecular simulations, such as energy minimization and molecular dynamics, and rotameric representation in the PDB, are used here on a heterodimeric coiled coil to investigate the dihedral angle distribution along the sequence. Different procedures have been used to build the structure, the quality assessment was based on the agreement between the simulated diffraction patterns and the experimental ones in the fingerprint region of coiled coils (5.15 A). The best one for building a realistic coiled coil structure consists of placing the side chains using molecular dynamics (MD) simulations, followed by side chain positioning using SMD or SCWRL procedures. The side chains and the backbone are equilibrated during the MD until they reach an equilibrium state for the t/g(+) ratio. Positioning the side chains on the resulting backbone, using the above procedures, gives rise to a well-defined 5.15 A meridian reflection.

Algorithms↗
PubMed2002

Structure and function of human stratum corneum under deformation.

BACKGROUND: The stratum corneum (SC) has an important barrier function. The effect of a mechanical stress applied to the SC is controversial on this important physiological parameter. OBJECTIVES AND METHODS: To assess both in vitro and in vivo the structure and function of human SC submitted to controlled strains, we measured the transepidermal water loss (TEWL), in vivo, on human skin submitted to controlled strains ranging from 0 to 20% extension imposed by a Densi-score device. We also looked at the structure of the SC by means of X-ray diffraction and transmission electron microscopy. RESULTS: Transmission electron microscopy and X-ray diffraction analysis were performed on harvested and stretched human SC. TEWL was not significantly influenced by the relative deformation applied to the skin. At high strain (60%) imposed in vitro to the SC, lipid bilayers and corneosomes were detached from corneocytes. Only rare corneosomes showed internal disruption. X-ray analysis did not reveal modifications in the supramolecular organization of intercellular lipids while stretching the SC. CONCLUSION: Submitting human SC to an extension force up to 20% elongation does not significantly alter the barrier function.

Adult↗
PubMed2001

Introducing the objective structured clinical examination to a general practice residency programme: results of a French pilot study.

OSCE for evaluating clinical competence still remains limited in France. This study presents the results of the first experimental use of an OSCE as a formative assessment of French general practice trainees. Fifty trainees rotated through a circuit of 15 standardized patient-based OSCE cases. Differences in scores were determined by analysis of variance. Reliability was calculated with the coefficient alpha. Pearson correlations were used to determine the relationship between station scores and overall OSCE score. Written questionnaires based on Likert-type scales were used to measure OSCE feasibility. No difference was found between total session scores. Significant item-total score correlations were found for 12 of the 15 clinical problems. The reliability of the examination was 0.58. Most participants agreed that the clinical situations were realistic, simulated patients were believable and sampling of cases was representative of general practice. These data confirm the feasibility of OSCE in assessing performance of general practice trainees. Optimal training of observers should improve examination reliability. This study warrants further development to confirm its usefulness as a summative assessment tool.

Journal Article↗
PubMedDate not supplied

[Are the prescriptions of anticholinesterasic drugs adapted to the associated diseases and/or drugs in the Alzheimer's dementia?].

The aim of this study was to evaluate if the prescriptions of anticholinesterase drugs took into account some diseases and drugs which could interfere with them, in 58 inpatients (82 years old). The anticholinesterase drugs were respectively at admission and discharge: donepezil (n = 27 and 34), galantamine (n = 12 and 19) and rivastigmine (n = 3 and 1). Nineteen patients received a combination of anticholinesterase drug with an anticholinergic drug (muscarinic antipsychotic 15 times). Twelve patients had a medical history which interfered with the anticholinesterase drug: uretroprostatic obstacle, chronic renal failure and auriculo-ventricular block. Thirty-five adverse drug reactions, mainly in digestive track, were recorded in 26 patients. The treatment with anticholinesterase drug was modified only in 18 patients and the combination of anticholinesterase drug and antipsychotic agent was stopped in 5 patients. In conclusion, inappropriated prescriptions of anticholinesterase drugs seem frequent, with a more important prevalence of adverse drug reactions than in prospective studies. These results incite to develop studies of evaluation of prescriptions of anticholinesterase drugs.

Aged↗