From polymer chemistry to structural biology: The development of SMA and related amphipathic polymers for membrane protein extraction and solubilisation

Abstract

Nanoparticles assembled with poly(styrene-maleic acid) copolymers, identified in the literature as Lipodisq, SMALPs or Native Nanodisc, are routinely used as membrane mimetics to stabilise protein structures in their native conformation. To date, transmembrane proteins of varying complexity (up to 8 beta strands or 48 alpha helices) and of a range of molecular weights (from 27 kDa up to 500 kDa) have been incorporated into this particle system for structural and functional studies. SMA and related amphipathic polymers have become versatile components of the biochemist's tool kit for the stabilisation, extraction and structural characterization of membrane proteins by techniques including cryo-EM and X-ray crystallography. Lipodisq formation does not require the use of conventional detergents and thus avoids their associated detrimental consequences. Here the development of this technology, from its fundamental concept and design to the diverse range of experimental methodologies to which it can now be applied, will be reviewed.

Physicochemical characterization, toxicity andin vivobiodistribution studies of a discoidal, lipid-based drug delivery vehicle: Lipodisq nanoparticles containing doxorubicin

“…Lipodisq NPs containing DOX were formed by the addition of SMA polymer to liposome suspensions containing the drug. The self-assembly of the discoidal particles is spontaneous and is driven by hydrophobic interactions, as the styrene groups of the polymer interact directly with the non-polar lipid tails [10]. NP formation was verified by dynamic light scattering and all Lipodisq preparations containing DOX were found to have a similar size with a diameter of 10 ± 2 nm (data not shown) [11].…”

“…Here we evaluate the ability of Lipodisq NPs (10 nm in diameter, 4.5 nm thickness) composed of a hydrolysed co-polymer of styrene and maleic anhydride (SMA) [10] and 1,2dimyristoyl-sn-glycero-3-phosphocholine (DMPC; PC 14:0/14:0) [11,12], to act as drug delivery vehicles for DOX. Since the Lipodisq nanoparticles are much smaller (10 -20 nm) than the FDA approved liposomes (>50 nm), it is possible that Lipodisq NPs will give a higher uptake of drugs in tumors and better penetration into the tumor tissue.…”

“…Several side effects are observed in patients treated with DOX, such as nausea, skin irritation and fever, the most dramatic being heart failure (cardiomyopathy) [15,17]. SMA polymer has been used extensively in structural biology to extract proteins directly from native membranes without the need for conventional detergents [10,11]. The resulting Lipodisq NPs (also known as SMALPs), consisting of a coin-shaped lipid bilayer stabilised by a polymer annulus [11] are used extensively for characterisation of integral membrane proteins by different techniques, including cryo electron microscopy and X-ray crystallography [10].…”

“…SMA polymer has been used extensively in structural biology to extract proteins directly from native membranes without the need for conventional detergents [10,11]. The resulting Lipodisq NPs (also known as SMALPs), consisting of a coin-shaped lipid bilayer stabilised by a polymer annulus [11] are used extensively for characterisation of integral membrane proteins by different techniques, including cryo electron microscopy and X-ray crystallography [10]. Hydrophobic 5 interactions drive the spontaneous self-assembly of Lipodisq NPs in aqueous conditions, creating a monodisperse suspension at physiological pH, temperature and ionic strength [10,18].…”

“…Here we evaluate the ability of Lipodisq NPs composed of a hydrolysed co-polymer of styrene and maleic anhydride (SMA) [10] and 1,2-dimyristoyl-sn-glycero-3phosphocholine (DMPC; PC 14:0/14:0) [11,12], to act as drug delivery vehicles for DOX.…”