title: Probing water accessibility in HET-s(218-289) amyloid fibrils by solid-state NMR.
abstract: Despite the importance of protein fibrils in the context of conformational diseases, information on their structure is still sparse. Hydrogen/deuterium exchange measurements of backbone amide protons allow the identification hydrogen-bonding patterns and reveal pertinent information on the amyloid β-sheet architecture. However, they provide only little information on the identity of residues exposed to solvent or buried inside the fibril core. NMR spectroscopy is a potent method for identifying solvent-accessible residues in proteins via observation of polarization transfer between chemically exchanging side-chain protons and water protons. We show here that the combined use of highly deuterated samples and fast magic-angle spinning greatly attenuates unwanted spin diffusion and allows identification of polarization exchange with the solvent in a site-specific manner. We apply this measurement protocol to HET-s(218-289) prion fibrils under different conditions (including physiological pH, where protofibrils assemble together into thicker fibrils) and demonstrate that each protofibril of HET-s(218-289), is surrounded by water, thus excluding the existence of extended dry interfibril contacts. We also show that exchangeable side-chain protons inside the hydrophobic core of HET-s(218-289) do not exchange over time intervals of weeks to months. The experiments proposed in this study can provide insight into the detailed structural features of amyloid fibrils in general.
authors.affiliation: Physical Chemistry, ETH Zürich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
authors.forename: Hélène
authors.initials: H
authors.lastname: Van Melckebeke
authors.forename: Paul
authors.initials: P
authors.lastname: Schanda
authors.forename: Julia
authors.initials: J
authors.lastname: Gath
authors.forename: Christian
authors.initials: C
authors.lastname: Wasmer
authors.forename: René
authors.initials: R
authors.lastname: Verel
authors.forename: Adam
authors.initials: A
authors.lastname: Lange
authors.forename: Beat H
authors.initials: BH
authors.lastname: Meier
authors.forename: Anja
authors.initials: A
authors.lastname: Böckmann
mesh_terms: D000682:Amyloid / Q000737:chemistry*; D041961:Deuterium Exchange Measurement; D005656:Fungal Proteins / Q000737:chemistry*; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011328:Prions / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000682:Amyloid; D005656:Fungal Proteins; C083891:HET-S protein, Podospora anserina; D011328:Prions; D014867:Water