Adsorption of a styrene maleic acid (SMA) copolymer-stabilized phospholipid nanodisc on a solid-supported planar lipid bilayer

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Abstract

Over recent years, there has been a rapid development of membrane-mimetic systems to encapsulate and stabilize planar segments of phospholipid bilayers in solution. One such system has been the use of amphipathic copolymers to solubilize lipid bilayers into nanodiscs. The attractiveness of this system, in part, stems from the capability of these polymers to solubilize membrane proteins directly from the host cell membrane. The assumption has been that the native lipid annulus remains intact, with nanodiscs providing a snapshot of the lipid environment. Recent studies have provided evidence that phospholipids can exchange from the nanodiscs with either lipids at interfaces, or with other nanodiscs in bulk solution. Here we investigate kinetics of lipid exchange between three recently studied polymer-stabilized nanodiscs and supported lipid bilayers at the silicon-water interface. We show that lipid and polymer exchange occurs in all nanodiscs tested, although the rate and extent differs between different nanodisc types. Furthermore, we observe adsorption of nanodiscs to the supported lipid bilayer for one nanodisc system which used a polymer made using reversible addition-fragmentation chain transfer polymerization. These results have important implications in applications of polymer-stabilized nanodiscs, such as in the fabrication of solid-supported films containing membrane proteins.

Abbreviations

ATR-FTIR
attenuated total reflection Fourier transform infrared
dDMPC
1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine
DMPC
1,2-dimyristoyl-sn-glycero-3-phosphocholine
MCMC
Markov chain Monte Carlo
MP
membrane protein
MSP
membrane scaffold protein
MWCO
molecular weight cut-off
NaOAc
sodium acetate
NR
neutron reflectometry
RAFT
reversible addition-fragmentation chain transfer
RAFT-SMA
RAFT-synthesised SMA
SEC
size exclusion chromatography
SiMW
silicon-matched water
SLD
scattering length density
SMA
poly(styrene-co-maleic acid)
SMALP
SMA lipid particle
SMAnh
poly(styrene-co-maleic anhydride)
SMI
poly(styrene-co-maleimide)
SMILP
SMI lipid particle

Keywords

Supported lipid bilayer
Polymer-stabilized phospholipid nanodisc
styrene-maleic acid lipid particle (SMALP)
styrene maleic acid (SMA)
Neutron reflectometry
Lipid exchange
Adsorption

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Present Addresses: Department of Chemistry, University of Warwick, Gibbet Hill, Coventry, CV4 7AL, UK.