[show abstract][hide abstract] ABSTRACT: When exceptionally preserved, hairs, wools, the skin stratum corneum and avian feathers can provide a wealth of archaeological and paleontological information. Long-term preservation of their information potential lies in the taphonomy (long-term behaviour laws) of keratin-based fibres and films. Here, we study the microscopic properties of archaeological hairs from the mediaeval burial of Marie de Bretagne (15th c., Orléans, France) preserved in a temperate environment, using complementary laboratory and synchrotron-based analytical instruments. We show that (a) the fibrillar keratin content of hair is exceptionally well preserved yet with limited degradation of the hair outer cortex in some hair strands, (b) exceptional preservation is attributed to the diffusion of copper and lead in the hair, (c) a posteriori examination led to the discovery of fragments of copper-based artefacts. We propose a possible scenario that led to the preservation of these tissues and discuss the archaeological interpretation of the microtaphonomy of these bioarchaeological remains.
Journal of Archaeological Science 02/2014; 42:487-499. · 1.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: Mechanics is now recognized as crucial in cell function. To date, the mechanical properties of cells have been inferred from experiments which investigate the roles of actin and microtubules ignoring the intermediate filaments (IFs) contribution. Here, we analyse myoblasts behaviour in the context of myofibrillar myopathy resulting from p.D399Y desmin mutation which disorganizes the desmin IF network in muscle cells. We compare the response of myoblasts expressing either mutated or wild-type desmin to cyclic stretch. Cells are cultivated on supports submitted to periodic uniaxial stretch of 20% elongation amplitude and 0.3 Hz frequency. We show that during stretching cycles, cells expressing mutated desmin reduce their mean amplitude both for the elongation and spreading area compared to those expressing wild-type desmin. Even more unexpected, the reorientation angles are altered in the presence of p.D399Y desmin. Yet, at rest, the whole set of those parameters are similar for the two cell populations. Thus, we demonstrate that IFs affect the mechanical properties and the dynamics of cell reorientation. Since these processes are known due to actin cytoskeleton, these results suggest the IFs implication in mechanics signal transduction. Further studies may lead to better understanding of their contribution to this process.
[show abstract][hide abstract] ABSTRACT: Amyloidoses are increasingly recognized as a major public health concern in Western countries. All amyloidoses share common morphological, structural, and tinctorial properties. These consist of staining by specific dyes, a fibrillar aspect in electron microscopy and a typical cross-β folding in x-ray diffraction patterns. Most studies that aim at deciphering the amyloid structure rely on fibers generated in vitro or extracted from tissues using protocols that may modify their intrinsic structure. Therefore, the fine details of the in situ architecture of the deposits remain unknown. Here, we present to our knowledge the first data obtained on ex vivo human renal tissue sections using x-ray microdiffraction. The typical cross-β features from fixed paraffin-embedded samples are similar to those formed in vitro or extracted from tissues. Moreover, the fiber orientation maps obtained across glomerular sections reveal an intrinsic texture that is correlated with the glomerulus morphology. These results are of the highest importance to understanding the formation of amyloid deposits and are thus expected to trigger new incentives for tissue investigation. Moreover, the access to intrinsic structural parameters such as fiber size and orientation using synchrotron x-ray microdiffraction, could provide valuable information concerning in situ mechanisms and deposit formation with potential benefits for diagnostic and therapeutic purposes.
[show abstract][hide abstract] ABSTRACT: A characteristic feature of the dense phases formed by fiber-shaped molecules is their organization into parallel rods packed in a hexagonal or pseudo-hexagonal lateral network. This is typically the case for the collagen triple helices inside fibrils, as confirmed by recent X-ray diffraction experiments carried out on highly crystallized fibers obtained by immersing the freshly extracted fibers in a salt-controlled medium. However such diffraction patterns also generally exhibit additional features in the form of diffuse scattering, which is a clear signature of a low degree of lateral ordering. Only few studies have analyzed and modeled the lateral packing of collagen triple helices when the structure is disordered. Some authors have used the concept of short-range order but this approach does not contain any echo of a hexagonal order. In this study, we use an analytical expression derived from the paracrystal model which retains the hexagonal symmetry information and leads to a good agreement with the experimental data in the medium-angle region. This method is quite sensitive to the degree of disorder and to the inter-object distance. One clear result is that the shift in peak positions, generally attributed to variations in intermolecular distances, can also arise from a change in the degree of ordering without any significant modification of the distances. This underlines the importance of evaluating the degree of ordering before attributing a shift in peak position to a change in the unit-cell. This method is generic and can be applied to any system composed of rod-shaped molecules.
Journal of Structural Biology 02/2011; 173(2):197-201. · 3.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: The purpose of this study was to characterize the effect of TIEG1 on the molecular structure of collagen within tail tendon fibers using 3-mo-old female C57BL/6 wild-type (WT) and TIEG1 KO mice. Synchrotron X-ray microdiffraction experiments were carried out on single tendon fibers extracted from the WT and TIEG1 KO dorsal tail tendon. The fibers were scanned in the radial direction, and X-ray patterns were obtained. From these patterns, the meridional direction was analyzed through X-ray intensity profile. In addition, collagen content was investigated using hydroxyproline assays, and qualitative real-time PCR experiments were performed on RNA isolated from fibroblasts to examine specific gene expression changes. The results showed different X-ray diffraction patterns between WT and TIEG1 KO tendon fibers, indicating a disorganization of the collagen structure for the TIEG1 KO compared with WT mice. Furthermore, the analyses of the X-ray intensity profiles exhibited a higher (23 A) period of collagen for the TIEG1 KO compared with the WT mice. The results of the hydroxyproline assays revealed a significant decrease in the TIEG1 KO compared with WT mice, leading to a decrease in the total amount of collagen present within the TIEG1 KO tendons. Moreover, qualitative real-time PCR results showed differences in the expression profiles of specific genes known to play important roles in tendon fiber development. These data further elucidate the role of TIEG1 on tendon structure and could explain the previous defects in the structure-function relationship found for TIEG1 KO tendon fibers.
Journal of Applied Physiology 04/2010; 108(6):1706-10. · 3.48 Impact Factor
[show abstract][hide abstract] ABSTRACT: X-rays interact strongly with biological organisms. Synchrotron radiation sources deliver very intense X-ray photon fluxes within micro- or submicro cross-section beams, resulting in doses larger than the MGy. The relevance of synchrotron radiation analyses of biological materials is therefore questionable since such doses, million times higher than the ones used in radiotherapy, can cause huge damages in tissues, with regard to not only DNA, but also proteic and lipid organizations. Very few data concerning the effect of very high X-ray doses in tissues are available in the literature. We present here an analysis of the structural phenomena which occur when the model tissue of human hair is irradiated by a synchrotron X-ray micro-beam. The choice of hair is supported by its hierarchical and partially ordered keratin structure which can be analysed inside the tissue by X-ray diffraction. To assess the damages caused by hard X-ray micro-beams (1 microm(2) cross-section), short exposure time scattering SAXS/WAXS patterns have been recorded at beamline ID13 (ESRF) after various irradiation times. Various modifications of the scattering patterns are observed, they provide fine insight of the radiation damages at various hierarchical levels and also unexpectedly provide information about the stability of the various hierarchical structural levels. It appears that the molecular level, i.e. the alpha helices which are stabilized by hydrogen bonds and the alpha-helical coiled coils which are stabilized by hydrophobic interactions, is more sensitive to radiation than the supramolecular architecture of the keratin filament and the filament packing within the keratin associated proteins matrix, which is stabilized by disulphide bonds.
Journal of Structural Biology 11/2009; 170(1):69-75. · 3.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: X-ray fluorescence microscopy (microXRF) is applied for the first time to study macrophages exposed to unpurified and purified single-walled (SW) and multiwalled (MW) carbon nanotubes (CNT). Investigating chemical elemental distributions allows one to (i) image nanotube localization within a cell and (ii) detect chemical modification of the cell after CNT internalization. An excess of calcium is detected for cells exposed to unpurified SWCNT and MWCNT and related toxicological assays are discussed.
[show abstract][hide abstract] ABSTRACT: 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.
Journal of Structural Biology 05/2006; 154(1):79-88. · 3.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: The soluble protein Ure2p from the yeast Saccharomyces cerevisiae assembles in vitro into straight and insoluble protein fibrils, through subtle changes of conformation. Whereas the structure of soluble Ure2p has been revealed by X-ray crystallography, further characterization of the structure of insoluble Ure2p fibrils is needed. We performed X-ray absorption near-edge spectroscopy (XANES) at the sulfur K-edge to probe the state of Cys221 in the fibrillar form of Ure2pC221 and provide structural information on the structure of Ure2p within fibrils. Although the Ure2p dimer dissociation into its constituent monomers has proven to be a prerequisite for assembly into fibrils, we showed the ability of every Ure2pC221 monomer to establish disulfide bonds upon incubation of the fibrils under oxidizing conditions. Our result indicates either that the constituent unit of the fibrillar form of the protein is a dimeric Ure2p or that the fibrils are made of protofilaments assembled in such a way that the residue C221 from a Ure2p molecule in one protofilament is located in the vicinity of a C221 residue from another molecule belonging to a neighbor protofilament.
Journal of Molecular Biology 04/2006; 356(4):843-9. · 3.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: 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.
Journal of Structural Biology 07/2005; 150(3):284-99. · 3.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: The putative transformation of alpha-helices into beta-sheets has been studied for more than 50 years in the case of hard alpha-keratin. In a previous study of stretched keratin fibers, we specified the conditions for beta-sheet appearance within horsehair: the formation of beta-sheets requires at least 30% relative humidity. However, this phenomenon was observed in the whole tissue. Then there was no clear chemical identification of the beta-sheets (keratin or matrix proteins) and the exact location of the beta-sheets across the fiber could not be specified. In this study, using wide-angle x-ray scattering and high spatial resolution infrared microspectroscopy, we could determine and characterize the structural elements across hair sections stretched in water, which provides new information about the aforementioned transition. Our results show that the process can be split into three steps: 1), unraveling of the alpha-helical coiled-coil domains, which starts at roughly 5% macroscopic strain; 2), further transformation of the unraveled coiled-coils into beta-sheet structures, which occurs above roughly 20% macroscopic strain; and 3), spatial expanding of the beta-structured zones from the sample center to its periphery.
[show abstract][hide abstract] ABSTRACT: 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.
[show abstract][hide abstract] ABSTRACT: Developments in microfocus synchrotron techniques have led to new results regarding the long-term alteration of archaeological samples of biological origin. Here, ancient hair samples from two Egyptian mummies have been analyzed using a conjunction of structural and elemental synchrotron methods. In this favored context of conservation, structural analysis revealed a remarkable preservation of keratin supramolecular organization at any observed length scale. Bulk keratin structure has therefore not been modified significantly over 2000 years. However, infrared spectroscopy indicated a partial disorganization of keratins close to the hair surface through polypeptide bond breakage. Elemental mapping showed a strongly heterogeneous distribution which can be related to mummification and cosmetic treatments.
[show abstract][hide abstract] ABSTRACT: 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.
Journal of Structural Biology 06/2003; 142(2):272-80. · 3.36 Impact Factor