Current Developments in Native Nanometric Discoidal Membrane Bilayer Formed by Amphipathic Polymers

Abstract

Unlike cytosolic proteins, membrane proteins (MPs) are embedded within the plasma membrane and the lipid bilayer of intracellular organelles. MPs serve in various cellular processes and account for over 65% of the current drug targets. The development of membrane mimetic systems such as bicelles, short synthetic polymers or amphipols, and membrane scaffold proteins (MSP)-based nanodiscs has facilitated the accommodation of synthetic lipids to stabilize MPs, yet the preparation of these membrane mimetics remains detergent-dependent. Bio-inspired synthetic polymers present an invaluable tool for excision and liberation of superstructures of MPs and their surrounding annular lipid bilayer in the nanometric discoidal assemblies. In this article, we discuss the significance of self-assembling process in design of biomimetic systems, review development of multiple series of amphipathic polymers and the significance of these polymeric “belts” in biomedical research in particular in unraveling the structures, dynamics and functions of several high-value membrane protein targets.

Insights into the Role of Membrane Lipids in the Structure, Function and Regulation of Integral Membrane Proteins

“…Nanodiscs are membrane mimetic systems formed from a membrane scaffold protein, exogenous lipids and the target protein, with the scaffold protein wrapping around the complex of lipids and protein. This arrangement shields the protein from aqueous solution and produces a more native-like environment than detergent micelles whilst also allowing ready variation of the lipid composition [80,81]. The results of the study on LacY and XylE revealed that in the presence of PE both transporters were preferentially in the inward-facing conformational state.…”

Characterization of Divalent Cation Interactions with AASTY Nanodiscs

“…However, detergent solubilization can be too harsh for membrane proteins or complexes as the detergent strips the majority of endogenous lipids and cofactors from the proteins. − Several approaches for relipidating the detergent solubilized membrane protein and reconstituting it into a bilayer mimicking environment have been developed, including membrane scaffold protein (MSP) nanodiscs, saposin-lipoprotein (Salipro) nanoparticles, and peptidiscs. − In recent years, amphiphilic copolymers have emerged as an attractive alternative to detergents, as they enable direct solubilization of membrane proteins encapsulated by a patch of the surrounding lipid bilayer from the membrane into so-called native nanodiscs. , With the native nanodisc approach, the membrane protein remains lipidated, and endogenous lipids and cofactors are preserved around it. Styrene-maleic acid (SMA) copolymers (Figure A) were the first to be used for the generation of native nanodiscs, and their use remains widespread. , While the native nanodisc approach shows great promise, there are significant shortcomings with the currently used copolymers. These include their negative charge and heterogeneity in terms of molecular weight and monomer sequence, which altogether limit the applicability of the method to a wider range of protein targets .…”

“…Alternative copolymers, which try to ameliorate these challenges have been published, including poly­(diisobutylene- co -maleic acid) (DIBMA), polymethacrylate (PMA), stilbene–maleic anhydride (STMA), and various SMA derivative copolymers, − as well as a noncharged inulin derivative . The current developments in native nanodiscs have recently been reviewed by, e.g., Brown et al and Esmaili et al…”

“…Styrene-maleic acid (SMA) copolymers (Figure 1A) were the first to be used for the generation of native nanodiscs, and their use remains widespread. 8,9 While the native nanodisc approach shows great promise, there are significant shortcomings with the currently used copolymers. These include their negative charge and heterogeneity in terms of molecular weight and monomer sequence, which altogether limit the applicability of the method to a wider range of protein targets.…”

“…10 Alternative copolymers, which try to ameliorate these challenges have been published, including poly(diisobutyleneco-maleic acid) (DIBMA), 11 polymethacrylate (PMA), 12 stilbene−maleic anhydride (STMA), 13 and various SMA derivative copolymers, 14−17 as well as a noncharged inulin derivative. 18 The current developments in native nanodiscs have recently been reviewed by, e.g., Brown et al 2 and Esmaili et al 9 We previously showed that poly(acrylic acid-co-styrene) (AASTY) copolymers (Figure 1B) are effective at solubilizing small, unilameller vesicles (SUVs) as well as extracting a model membrane protein from HEK293 cells. 19 AASTY can be synthesized by reversible addition−fragmentation chain-transfer (RAFT) polymerizations, which allow the control of copolymer length and the dispersity of size, compared with free-radical polymerization.…”