The fundamental importance of membrane proteins in drug discovery has meant that membrane mimetic systems for studying membrane proteins are of increasing interest. One such system has been the amphipathic, negatively charged poly(styrene-co-maleic acid) (SMA) polymer to form “SMA Lipid Particles” (SMALPs) which have been widely adopted to solubilize membrane proteins directly from the cell membrane. However, SMALPs are only soluble under basic conditions and precipitate in the presence of divalent cations required for many downstream applications. Here, we show that the positively charged poly(styrene-co-maleimide) (SMI) forms similar nanoparticles with comparable efficiency to SMA, whilst remaining functional at acidic pH and compatible with high concentrations of divalent cations. We have performed a detailed characterization of the performance of SMI that enables a direct comparison with similar data published for SMA. We also demonstrate that SMI is capable of extracting proteins directly from the cell membrane and can solubilize functional human G-protein coupled receptors (GPCRs) expressed in cultured HEK 293T cells. “SMILPs” thus provide an alternative membrane solubilization method that successfully overcomes some of the limitations of the SMALP method.
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Funding: This work has been supported by an Engineering and
Physical Sciences Research Council (EPSRC: EP/M506461/1)
and Diamond Light Source studentship for SCLH and funding
from the Biotechnology and Biological Sciences Research
Council (BBSRC: BB/M018261/1 [TRD], BB/J017310/1 [TRD and
MW], BB/1020349/1 [MW and TRD], BB/P009840/1 [TJK] and
BB/L00335X/1 [TJK]). CT acknowledges STFC BioMedNet (studentship
agreement #2990) and the University of Bath for PhD
studentship funding. The Medical Research Council (MRC)
and AstraZeneca are thanked for supporting JC with a CASE
award to MW. ECB thanks the University of Bristol for PhD studentship