MOMD Analysis of NMR Lineshapes from A?-Amyloid Fibrils: A New Tool for Characterizing Molecular Environments in Protein Aggregates.
MOMD Analysis of NMR Lineshapes from A?-Amyloid Fibrils: A New Tool for Characterizing Molecular Environments in Protein Aggregates.
J Phys Chem B. 2018 Apr 06;:
Authors: Meirovitch E, Liang Z, Freed JH
Abstract
The microscopic-order-macroscopic-disorder (MOMD) approach for 2H NMR lineshape analysis is applied to dry and hydrated 3-fold-, and 2-fold-symmetric amyloid-A?40 fibrils, and protofibrils of the D23N mutant. The methyl-moieties of L17, L34, V36 (C-CD3) and M35 (S-CD3) serve as probes. Experimental 2H spectra acquired previously in the 147-310 K range are used. MOMD describes local probe motion as axial diffusion ( R-tensor) in the presence of a potential, u, which represents the spatial restrictions exerted by the molecular surroundings. We find that Rpar = (0.2-3.3)×104 s-1, Rperp = (2.2-2.5)×102 s-1, and R is tilted from the 2H quadrupolar tensor at 60o-75o. The strength of u is in the (2.0-2.4) kT range; its rhombicity is substantial. The only methyl-moieties affected by fibril-hydration are those of M35, located at fibril interfaces. The associated local potentials change form abruptly around 260 K, where massive water-freezing occurs. An independent study revealed unfrozen "tightly-peptide-bound" water residing at the interfaces of the 3-fold-symmetric A?40 fibrils, and the interfaces of the E22G and E22? A?40-mutant fibrils. Considering this to be the case in general for A?40-related fibrils, the following emerges. The impact of water-freezing is transmitted selectively to the fibril structure through interactions with tightly-peptide-bound water, in this case of M35 methyl-moieties. The proof that such waters reside at the interfaces of the 2-fold-symmetric fibril, and the protofibril of the D23N mutant, is new. A prior interpretation of the same experimental 2H spectra differs substantially from ours. In particular, no information on key features associated with the surroundings of the NMR probe is obtained. Thus, MOMD analysis of NMR lineshapes as applied to amyloid fibrils/protein aggregates emerges as a consistent new tool for elucidating properties of/processes associated with molecular environments in the fibril.
PMID: 29624402 [PubMed - as supplied by publisher]
More...