The putative transformation of
α-helices into
β-sheets has been studied for more than 50 years in the case of hard
α-keratin. In a previous study of stretched keratin fibers, we specified the ...conditions for
β-sheet appearance within horsehair: the formation of
β-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
β-sheets (keratin or matrix proteins) and the exact location of the
β-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
α-helical coiled-coil domains, which starts at roughly 5% macroscopic strain; 2), further transformation of the unraveled coiled-coils into
β-sheet structures, which occurs above roughly 20% macroscopic strain; and 3), spatial expanding of the
β-structured zones from the sample center to its periphery.
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.
The mechanical behavior of human hair fibers is determined by the interactions between keratin proteins structured into microfibrils (hard
α-keratin intermediate filaments), a protein sulfur-rich ...matrix (intermediate filaments associated proteins), and water molecules. The structure of the microfibril-matrix assembly has already been fully characterized using electron microscopy and small-angle x-ray scattering on unstressed fibers. However, these results give only a static image of this assembly. To observe and characterize the deformation of the microfibrils and of the matrix, we have carried out time-resolved small-angle x-ray microdiffraction experiments on human hair fibers stretched at 45% relative humidity and in water. Three structural parameters were monitored and quantified: the 6.7-nm meridian arc, which is related to an axial separation between groups of molecules along the microfibrils, the microfibril’s radius, and the packing distance between microfibrils. Using a surface lattice model of the microfibril, we have described its deformation as a combination of a sliding process and a molecular stretching process. The radial contraction of the matrix is also emphasized, reinforcing the hydrophilic gel nature hypothesis.
New information about calcium status in human scalp hair shaft, deduced from X-ray micro-fluorescence imaging, including its distribution over the hair section, the existence of one or several ...binding-types and its variation between people, is presented. The existence of two different calcium types is inferred. The first one corresponds to atoms (or ions) easily removable by hydrochloric acid, located in the cortex (granules), in the cuticle zone and also in the core of the medulla, which can reasonably be identified as calcium soaps. The second type consists of non-easily removable calcium atoms (or ions) that are located in the medulla wall, probably also in the cuticle, and rather uniformly in the cortex; these calcium atoms may be involved in Ca
2+-binding proteins, and their concentration is fairly constant from one subject to another. In addition to its nonuniform distribution across the hair section, the second striking feature of the first type calcium content is its high variability from one subject to another, by up to a factor 10. We expect this information to be useful for analyzing in more detail the relationship between hair calcium and environmental and medical factors.
Breast-cancer diagnosis using hair Briki, Fatma; Busson, Bertrand; Salicru, Bruno ...
Nature (London),
07/1999, Letnik:
400, Številka:
6741
Journal Article
Recenzirano
Odprti dostop
James et al. observed a difference between the X-ray diffraction patterns of hair from healthy females and from breast-cancer patients. This difference was reported as the presence of an extra ring ...corresponding to a spacing of 4.44 nm on the patterns obtained from breast-cancer patients. This ring was also observed in patterns from subjects "not yet diagnosed with breast cancer but suspected of being at risk". James et al. proposed that these observations might lead to a screening method for breast cancer. We have now repeated the study using a different hair type (from the scalp), but are unable to replicate their observations.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Synopsis
Synchrotron‐based infrared microscopic measurements have been performed on various hair transverse sections, sampled either from the heads of Caucasian or Afro‐American subjects. Lipid ...content of various virgin hair transverse sections was established, with an unprecedented resolution. The variations in shape and intensity of the CH2, CH3, amide I and amide II bands, before and after lipid removal by solvent extraction, were profiled, showing clearly that Caucasian hair often contains lipids localized inside the medulla and to a lesser extent inside the cuticle. This statement does not hold for the Afro‐American hair analysed. For this, the FT‐IR spectra do not change within the hair section and are insensitive to solvent extraction. The importance of the origin of hair on its physical and chemical properties has to be taken into account in future investigations.
Résumé
Par utilisation de la microscopie infra‐rouge utilisant le rayonnement synchrotron, la répartition des lipides sur la section de cheveux vierges (caucasiens et afro‐américains), a pu être comparée avec une résolution spatiale jamais égalée. La forme et l'intensité des bandes CH2, CH3, amide I et amide II, avant et après délipidation par solvants ont été obtenues. Il apparaît que pour le cheveu caucasien, les lipides sont majoritairement localisés dans la médule et dans la cuticule en quantité moindre. Ceci n'est pas le cas pour les cheveux afro‐américains: leur spectre infra‐rouge est le même sur toute la section et est insensible à la délipidation. L'origine des cheveux est donc particulièrement importante pour l'étude de leurs propriétés physico‐chimiques.
A combined approach, using synchrotron radiation-based diffraction and infrared microspectrometry, has been used to study the structure and molecular composition of hair samples. These methods ...allowed us to get an insight at different structural scales into the composition and structure of hair. Firstly, information about the configuration of amino-acid residues was obtained at atomic scale, secondly, a model was presented for the geometry and the packing of the microfibrils at medium scale and finally different structural zones were evidenced by microdiffraction at macroscopic scale. We also showed that the two main components of hair--proteins and lipids--are not evenly distributed within the fiber. In addition, these two components exhibit different structure, depending upon their location. Moreover, diffraction and microdiffraction data indicate that the cuticle zone is mainly composed of lipid granules, whereas the cortex and the medulla zones are composed primarily of alpha-keratin. Infrared microspectroscopy, using an enhanced lateral resolution thanks to synchrotron radiation, indicates, on one hand, that the protein structure between the cuticle and cortex are different, and on the other hand, that the concentration of lipids, inside the medulla, is much higher than everywhere else. This work emphasizes the complementarity between both techniques, and highlights the potentialities they can offer in the case of various other studies in biology.
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
α-keratin intermediate filaments under in vivo conditions. In short, the
α-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.
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