title: Nano-scale morphology of melanosomes revealed by small-angle X-ray scattering.
abstract: Melanosomes are highly specialized organelles that produce and store the pigment melanin, thereby fulfilling essential functions within their host organism. Besides having obvious cosmetic consequences--determining the color of skin, hair and the iris--they contribute to photochemical protection from ultraviolet radiation, as well as to vision (by defining how much light enters the eye). Though melanosomes can be beneficial for health, abnormalities in their structure can lead to adverse effects. Knowledge of their ultrastructure will be crucial to gaining insight into the mechanisms that ultimately lead to melanosome-related diseases. However, due to their small size and electron-dense content, physiologically intact melanosomes are recalcitrant to study by common imaging techniques such as light and transmission electron microscopy. In contrast, X-ray-based methodologies offer both high spatial resolution and powerful penetrating capabilities, and thus are well suited to study the ultrastructure of electron-dense organelles in their natural, hydrated form. Here, we report on the application of small-angle X-ray scattering--a method effective in determining the three-dimensional structures of biomolecules--to whole, hydrated murine melanosomes. The use of complementary information from the scattering signal of a large ensemble of suspended organelles and from single, vitrified specimens revealed a melanosomal sub-structure whose surface and bulk properties differ in two commonly used inbred strains of laboratory mice. Whereas melanosomes in C57BL/6J mice have a well-defined surface and are densely packed with 40-nm units, their counterparts in DBA/2J mice feature a rough surface, are more granular and consist of 60-nm building blocks. The fact that these strains have different coat colors and distinct susceptibilities to pigment-related eye disease suggest that these differences in size and packing are of biological significance.
authors.affiliation: Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany; Applied Physical Chemistry, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany; Analytical Chemistry - Biointerfaces, Ruhr-University Bochum, Bochum, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gorniak
authors.affiliation: Applied Physical Chemistry, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany; Max-Planck-Institute for Intelligent Systems, Stuttgart, Germany.
authors.forename: Tamas
authors.initials: T
authors.lastname: Haraszti
authors.affiliation: Helmholtz-Zentrum Geesthacht, Zentrum für Material- und Küstenforschung GmbH, Geesthacht, Germany.
authors.forename: Vasyl M
authors.initials: VM
authors.lastname: Garamus
authors.affiliation: Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany; Applied Physical Chemistry, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany; Analytical Chemistry - Biointerfaces, Ruhr-University Bochum, Bochum, Germany.
authors.forename: Andreas R
authors.initials: AR
authors.lastname: Buck
authors.affiliation: Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany; Applied Physical Chemistry, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Senkbeil
authors.affiliation: Institute for X-Ray Physics, University of Göttingen, Göttingen, Germany.
authors.forename: Marius
authors.initials: M
authors.lastname: Priebe
authors.affiliation: Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, Iowa, United States of America; Center for the Prevention and Treatment of Visual Loss, Iowa City Veterans Affairs (VA) Health Care System, Iowa City, Iowa, United States of America.
authors.forename: Adam
authors.initials: A
authors.lastname: Hedberg-Buenz
authors.affiliation: Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Demelza
authors.initials: D
authors.lastname: Koehn
authors.affiliation: Institute for X-Ray Physics, University of Göttingen, Göttingen, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Salditt
authors.affiliation: Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany; Applied Physical Chemistry, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Grunze
authors.affiliation: Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, Iowa, United States of America; Center for the Prevention and Treatment of Visual Loss, Iowa City Veterans Affairs (VA) Health Care System, Iowa City, Iowa, United States of America.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Anderson
authors.affiliation: Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany; Applied Physical Chemistry, Ruprecht-Karls-University Heidelberg, Heidelberg, Germany; Analytical Chemistry - Biointerfaces, Ruhr-University Bochum, Bochum, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Rosenhahn
mesh_terms: D000818:Animals; D005612:Freeze Drying; D005838:Genotype; D008543:Melanins / Q000378:metabolism; D020460:Melanosomes / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D036103:Nanotechnology; D053838:Scattering, Small Angle; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D008543:Melanins