The Journal of Membrane Biology

, Volume 247, Issue 9, pp 897–908

Thermal Fluctuations in Amphipol A8-35 Particles: A Neutron Scattering and Molecular Dynamics Study

  • Moeava Tehei
  • Jason D. Perlmutter
  • Fabrice Giusti
  • Jonathan N. Sachs
  • Giuseppe Zaccai
  • Jean-Luc Popot
Article

DOI: 10.1007/s00232-014-9725-1

Cite this article as:
Tehei, M., Perlmutter, J.D., Giusti, F. et al. J Membrane Biol (2014) 247: 897. doi:10.1007/s00232-014-9725-1

Abstract

Amphipols are a class of polymeric surfactants that can stabilize membrane proteins in aqueous solutions as compared to detergents. A8-35, the best-characterized amphipol to date, is composed of a polyacrylate backbone with ~35 % of the carboxylates free, ~25 % grafted with octyl side-chains, and ~40 % with isopropyl ones. In aqueous solutions, A8-35 self-organizes into globular particles with a molecular mass of ~40 kDa. The thermal dynamics of A8-35 particles was measured by neutron scattering in the 10-picosecond, 18-picosecond, and 1-nanosecond time-scales on natural abundance and deuterium-labeled molecules, which permitted to separate backbone and side-chain motions. A parallel analysis was performed on molecular dynamics trajectories (Perlmutter et al., Langmuir 27:10523–10537, 2011). Experimental results and simulations converge, from their respective time-scales, to show that A8-35 particles feature a more fluid hydrophobic core, predominantly containing the octyl chains, and a more rigid solvent-exposed surface, made up predominantly of the hydrophilic polymer backbone. The fluidity of the core is comparable to that of the lipid environment around proteins in the center of biological membranes, as also measured by neutron scattering. The biological activity of proteins depends sensitively on molecular dynamics, which itself is strongly dependent on the immediate macromolecular environment. In this context, the characterization of A8-35 particle dynamics constitutes a step toward understanding the effect of amphipols on membrane protein stability and function.

Keywords

Membrane proteinsSurfactantsPolymersMolecular dynamicsQENS

Abbreviations

A8-35

An anionic amphipol of average molecular mass ~4.3 kDa, containing ~35 % free carboxylates, ~25 % octyl side-chains, and ~40 % isopropyl ones

APol

Amphipol

CAC

Critical association concentration

DAPol

A8-35 with per-deuterated side-chains

EINS

Elastic incoherent neutron scattering

HAPol

Natural abundance A8-35

INS

Inelastic neutron scattering

MD

Molecular dynamics

Mn

Number-averaged molecular mass

mQ water

Water purified on a A10 Advantage Millipore System

MSD

Mean square displacement

OmpA, OmpX

Respectively outer membrane proteins A and X from Escherichia coli

QENS

Quasi-elastic neutron scattering

RS

Stokes radius

SANS

Small-angle neutron scattering

SEC

Size exclusion chromatography

Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • Moeava Tehei
    • 1
  • Jason D. Perlmutter
    • 2
  • Fabrice Giusti
    • 3
  • Jonathan N. Sachs
    • 4
  • Giuseppe Zaccai
    • 5
    • 6
  • Jean-Luc Popot
    • 3
  1. 1.Centre for Medical Radiation Physics and Centre for Medical and Molecular Bioscience, University of WollongongWollongongAustralia
  2. 2.Department of PhysicsBrandeis UniversityWalthamUSA
  3. 3.UMR 7099, Centre National de la Recherche Scientifique/Université Paris-7 Institut de Biologie Physico-Chimique (FRC 550)ParisFrance
  4. 4.Department of Biomedical EngineeringUniversity of MinnesotaMinneapolisUSA
  5. 5.Institut de Biologie Structurale, CEA/CNRS/UJF UMR5075GrenobleFrance
  6. 6.Institut Laue LangevinGrenobleFrance