The conformation of the Congo-red ligand bound to amyloid fibrils HET-s(218–289): a solid-state NMR study
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We have previously shown that Congo red (CR) binds site specifically to amyloid fibrils formed by HET-s(218–289) with the long axis of the CR molecule almost parallel to the fibril axis. HADDOCK docking studies indicated that CR adopts a roughly planar conformation with the torsion angle ϕ characterizing the relative orientation of the two phenyl rings being a few degrees. In this study, we experimentally determine the torsion angle ϕ at the center of the CR molecule when bound to HET-s(218–289) amyloid fibrils using solid-state NMR tensor-correlation experiments. The method described here relies on the site-specific 13C labeling of CR and on the analysis of the two-dimensional magic-angle spinning tensor-correlation spectrum of 13C2-CR. We determined the torsion angle ϕ to be 19°.
KeywordsMAS Amyloid fibrils Congo red Rotor-synchronized tensor-correlation experiments
We would like to thank Albert A. Smith for helpful discussions. This work has been supported by the Swiss National Science Foundation SNF (Grant 200020_159707 and 200020_146757) and by the French ANR (ANR-14-CE09-0024B).
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