Molecular dynamics simulations of intrinsically disordered proteins (IDPs) can provide high resolution structural ensembles if the force field is accurate enough and if the simulation sufficiently samples the conformational space of the IDP with the correct weighting of sub-populations. Here, we investigate the combined force field–sampling problem by testing a standard force field as well as newer fixed charge force fields, the latter specifically motivated for better description of unfolded states and IDPs, and comparing them with a standard temperature replica exchange (TREx) protocol and a non-equilibrium Temperature Cool Walking (TCW) sampling algorithm. The force field and sampling combinations are used to characterize the structural ensembles of the amyloid-beta peptides Aβ42 and Aβ43, which both should be random coils as shown recently by experimental nuclear magnetic resonance (NMR) and 2D Förster resonance energy transfer (FRET) experiments. The results illustrate the key importance of the sampling algorithm: while the standard force field using TREx is in poor agreement with the NMR J-coupling and nuclear Overhauser effect and 2D FRET data, when using the TCW method, the standard and optimized protein-water force field combinations are in very good agreement with the same experimental data since the TCW sampling method produces qualitatively different ensembles than TREx. We also discuss the relative merit of the 2D FRET data when validating structural ensembles using the different force fields and sampling protocols investigated in this work for small IDPs such as the Aβ42 and Aβ43 peptides.
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14 March 2019
Research Article|
March 14 2019
The combined force field-sampling problem in simulations of disordered amyloid-β peptides
James Lincoff
;
James Lincoff
a)
1
Department of Chemical and Biomolecular Engineering, University of California
, Berkeley, California 94720, USA
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Sukanya Sasmal
;
Sukanya Sasmal
1
Department of Chemical and Biomolecular Engineering, University of California
, Berkeley, California 94720, USA
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Teresa Head-Gordon
Teresa Head-Gordon
c)
1
Department of Chemical and Biomolecular Engineering, University of California
, Berkeley, California 94720, USA
2
Department of Chemistry, University of California
, Berkeley, California 94720, USA
3
Department of Bioengineering, University of California
, Berkeley, California 94720, USA
4
Pitzer Theory Center, University of California
, Berkeley, California 94720, USA
c)Author to whom correspondence should be addressed: thg@berkeley.edu
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a)
Contributions: J. Lincoff and S. Sasmal contributed equally to this work.
b)
Current address: Department of Pharmaceutical Sciences, University of California, Irvine, California 92697, USA.
c)Author to whom correspondence should be addressed: thg@berkeley.edu
J. Chem. Phys. 150, 104108 (2019)
Article history
Received:
October 26 2018
Accepted:
February 20 2019
Citation
James Lincoff, Sukanya Sasmal, Teresa Head-Gordon; The combined force field-sampling problem in simulations of disordered amyloid-β peptides. J. Chem. Phys. 14 March 2019; 150 (10): 104108. https://doi.org/10.1063/1.5078615
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