Abstract
We have performed scanning nano-beam small-angle X-ray scattering (nano-SAXS) experiments on in vitro-formed actin filaments cross-linked with \(\upalpha\)-actinin. The experimental method combines a high resolution in reciprocal space with a real space resolution as given by the spot-size of the nano-focused X-ray beam, and opens up new opportunities to study local super-molecular structures of actin filaments. In this first proof-of-concept, we show that the local orientation of actin bundles formed by the cross-linking can be visualized by the X-ray darkfield maps. The filament bundles give rise to highly anisotropic diffraction patterns showing distinct streaks perpendicular to the bundle axes. Interestingly, some diffraction patterns exhibit a fine structure in the form of intensity modulations allowing for a more detailed analysis of the order within the bundles. A first empirical quantification of these modulations is included in the present work.
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Acknowledgments
We thank Christine Wurm and Andreas Bausch for an initial insight into actin preparation; Markus Osterhoff, Martin Krenkel, and Bastian Hartmann for their contributions to instrumentation and alignment of the GINIX instrument; Michael Sprung and Alexey Zozulya for excellent working conditions at the P10 beamline; and Sarah Köster for helpful discussions. Financial support by SFB 937/A11 of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.
Author contributions
T.S. designed the research, M.T. prepared the samples; all authors carried out the experiment; M.T. analyzed data; M.T. and T.S. wrote the manuscript.
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Töpperwien, M., Priebe, M. & Salditt, T. Actin bundles cross-linked with \(\upalpha\)-actinin studied by nanobeam X-ray diffraction. Eur Biophys J 45, 383–392 (2016). https://doi.org/10.1007/s00249-015-1107-9
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DOI: https://doi.org/10.1007/s00249-015-1107-9