title: Fast Collisional Lipid Transfer Among Polymer-Bounded Nanodiscs.
abstract: Some styrene/maleic acid (SMA) copolymers solubilise membrane lipids and proteins to form polymer-bounded nanodiscs termed SMA/lipid particles (SMALPs). Although SMALPs preserve a lipid-bilayer core, they appear to be more dynamic than other membrane mimics. We used time-resolved Förster resonance energy transfer and small-angle neutron scattering to determine the kinetics and the mechanisms of phospholipid transfer among SMALPs. In contrast with vesicles or protein-bounded nanodiscs, SMALPs exchange lipids not only by monomer diffusion but also by fast collisional transfer. Under typical experimental conditions, lipid exchange occurs within seconds in the case of SMALPs but takes minutes to days in the other bilayer particles. The diffusional and second-order collisional exchange rate constants for SMALPs at 30 °C are kdif= 0.287 s-1and kcol= 222 M-1s-1, respectively. Together with the fast kinetics, the observed invariability of the rate constants with probe hydrophobicity and the moderate activation enthalpy of ~70 kJ mol-1imply that lipids exchange through a "hydrocarbon continuum" enabled by the flexible nature of the SMA belt surrounding the lipid-bilayer core. Owing to their fast lipid-exchange kinetics, SMALPs represent highly dynamic equilibrium rather than kinetically trapped membrane mimics, which has important implications for studying protein/lipid interactions in polymer-bounded nanodiscs.
authors.affiliation: Molecular Biophysics, University of Kaiserslautern, Erwin-Schrödinger-Str. 13, 67663 Kaiserslautern, Germany.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Cuevas Arenas
authors.affiliation: Molecular Biophysics, University of Kaiserslautern, Erwin-Schrödinger-Str. 13, 67663 Kaiserslautern, Germany.
authors.forename: Bartholomäus
authors.initials: B
authors.lastname: Danielczak
authors.affiliation: Institut Max von Laue Paul Langevin, Grenoble, 38042, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Martel
authors.affiliation: Institut Max von Laue Paul Langevin, Grenoble, 38042, France.
authors.forename: Lionel
authors.initials: L
authors.lastname: Porcar
authors.affiliation: Institut de Biologie Structurale (IBS), Univ. Grenoble Alpes, CEA, CNRS, Grenoble, 38044, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Breyton
authors.affiliation: Institut de Biologie Structurale (IBS), Univ. Grenoble Alpes, CEA, CNRS, Grenoble, 38044, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Ebel
authors.affiliation: Molecular Biophysics, University of Kaiserslautern, Erwin-Schrödinger-Str. 13, 67663 Kaiserslautern, Germany.
authors.forename: Sandro
authors.initials: S
authors.lastname: Keller