Solubilization of Membrane Proteins into Functional Lipid‐Bilayer Nanodiscs Using a Diisobutylene/Maleic Acid Copolymer

Abstract

Once removed from their natural environment, membrane proteins depend on membrane‐mimetic systems to retain their native structures and functions. To this end, lipid‐bilayer nanodiscs that are bounded by scaffold proteins or amphiphilic polymers such as styrene/maleic acid (SMA) copolymers have been introduced as alternatives to detergent micelles and liposomes for in vitro membrane‐protein research. Herein, we show that an alternating diisobutylene/maleic acid (DIBMA) copolymer shows equal performance to SMA in solubilizing phospholipids, stabilizes an integral membrane enzyme in functional bilayer nanodiscs, and extracts proteins of various sizes directly from cellular membranes. Unlike aromatic SMA, aliphatic DIBMA has only a mild effect on lipid acyl‐chain order, does not interfere with optical spectroscopy in the far‐UV range, and does not precipitate in the presence of low millimolar concentrations of divalent cations.

Fast Collisional Lipid Transfer Among Polymer-Bounded Nanodiscs

“…2a). Since SMA(3:1) has been found518 to lower the gel-to-fluid transition temperature of DMPC, the lipid bilayers in the SMALP core were always in the fluid state, as confirmed calorimetrically (Supplementary Fig. 1).…”

“…Owing to their small size, SMALPs are well suited for optical-spectroscopic13489121415 and chromatographic13151617 techniques. Likewise, a diisobutylene/maleic acid (DIBMA) copolymer has been found18 to solubilise membrane proteins and lipids in a mild fashion, that is, without major perturbation of the bilayer order in DIBMA/lipid particles (DIBMALPs).…”

Bioinspired, Size‐Tunable Self‐Assembly of Polymer–Lipid Bilayer Nanodiscs

“…The amphiphilic belt is critical for the stability and function of nanodiscs. Studies have reported different types of surrounding belts including Membrane Scaffold proteins (MSPs) [5, 7] , peptides [8] , and polymer [9] . Even though MSP-based nanodiscs are excellent mimics of the membrane, the reconstitution of a membrane protein still requires the undesirable use of detergents [10] , and therefore detergent-free solubilization of membrane proteins attracted new attention in the field [11, 12] .…”

Membrane biology visualized in nanometer-sized discs formed by styrene maleic acid polymers

“…Due to their large sizes, liposomes exhibit completely broadened phosphorus-31 NMR signals, while rapidly tumbling nanodiscs yield sharp signals for contained phospholipids. The transition is sharp, moving rapidly from onset to completion of membrane solubilization with only a neglible concentration of free polymer DIBMA [23]. The proton NMR spectra of the polymer and contained proteins are broadened due to the polydispersity of the polymers and heterogeneity of the assemblies [1].…”

“…An alternative to SMA polymers with aliphatic rather than aromatic moieties was recently found by Sandro Keller and colleagues [23] to more gently extract membrane proteins. It offers alternating diisobutylene and maleic acid sidechains that are less perturbing to native naodiscs and hence may be advantageous for solubilizing particularly labile protein complexes.…”