Phenyl-Ring Dynamics in Amyloid Fibrils and Proteins: The Microscopic-Order-Macroscopic-Disorder Perspective

Eva Meirovitch, Zhichun Liang, Jack H. Freed

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6 Scopus citations


We have developed the microscopic-order-macroscopic-disorder (MOMD) approach for studying internal mobility in polycrystalline proteins with 2H lineshape analysis. The motion itself is expressed by a diffusion tensor, R, the local spatial restraints by a potential, u, and the "local geometry" by the relative orientation of the model-related and nuclear magnetic resonance-related tensors. Here, we apply MOMD to phenyl-ring dynamics in several δβ40-amyloid-fibrils, and the villin headpiece subdomain (HP36). Because the available data are limited in extent and sensitivity, we adjust u and R in the relevant parameter ranges, fixing the "local geometry" in accordance with standard stereochemistry. This yields a physically well-defined and consistent picture of phenyl-ring dynamics, enabling comparison between different systems. In the temperature range of 278-308 K, u has a strength of (1.7-1.8) kT and a rhombicity of (2.4-2.6) kT, and R has components of 5.0 × 102 ≤ R ≤ 2.0 × 103 s-1 and 6.3 × 105 ≤ R ≤ 2.0 × 106 s-1. At 278 K, fibril hydration increases the axiality of both u and R; HP36 hydration has a similar effect at 295 K, reducing R considerably. The D23N mutation slows down the motion of the probe; Aβ40 polymorphism affects both this motion and the related local potential. The present study identifies the impact of various factors on phenyl-ring mobility in amyloid fibrils and globular proteins; the difference between the two protein forms is considerable. The distinctive impact of hydration on phenyl-ring motion and previously studied methyl-group motion is also examined. The 2H lineshapes considered here were analyzed previously with various multi-simple-mode (MSM) models, where several simple motional modes are combined. The MOMD and MSM interpretations differ in essence.

Original languageEnglish
Pages (from-to)8675-8684
Number of pages10
JournalJournal of Physical Chemistry B
Issue number37
StatePublished - 20 Sep 2018

Bibliographical note

Publisher Copyright:
Copyright © 2018 American Chemical Society.


This work was supported by the IsraelU.S.A. Binational Science Foundation (grant no. 2016097 to E.M. and J.H.F.) and the Israel Science Foundation (grant no. 469/15 to E.M.). This work was also supported by NIH/NIGMS grant P41GM103521 to J.H.F.

FundersFunder number
IsraelU.S.A. Binational Science Foundation2016097
National Institute of General Medical SciencesP41GM103521
Israel Science Foundation469/15


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