Application of the SMALP technology to the isolation of GPCRs from low-yielding cell lines

Accepted Manuscript version. The Published Journal Article is available on Biochimica et Biophysica Acta (BBA) - Biomembranes, Volume 1863, Issue 9, Article number 183641 (DOI: https://doi.org/10.1016/j.bbamem.2021.183641). Supplementary Material available free of charge on the article webpage.
© 2021. This Manuscript version is made available under the CC-BY-NC-ND 4.0 license. https://creativecommons.org/licenses/by-nc-nd/4.0/

ABSTRACT

The ability of styrene–maleic acid (SMAc) co-polymers to spontaneously insert into biological membranes can be exploited to extract G protein-coupled receptors (GPCRs) embedded in styrene–maleic acid lipid particles (SMALPs), preserving the native environment around the protein and thus enhancing the feasibility 20 of functional studies. So far, the SMALP technology has been primarily employed on non-mammalian cells and protocols are not optimized for adherent human cell lines, which cannot be harvested in large amounts. In this work, a fine investigation of key parameters affecting the formation of SMALPs was undertaken with the purpose of maximizing the yield of extraction of a recombinant form of human β2-adrenergic receptor (rhβ2AR) from HEK293T cells. The study highlighted an important influence of ionic strength on the 25 membrane solubilization efficiency and GPCR purification yield of SMAc co-polymers: by lowering the salt concentration of all buffers used in previously published SMALP protocols, the water solubility and extraction efficiency of the selected SMAc co-polymer (commercially supplied as a potassium salt) were enhanced. In-line combination of size-exclusion chromatography (SEC) with immobilized metal affinity chromatography (IMAC) allowed further improvement of the final rhβ2AR yield by reducing the loss of 30 SMALP-embedded GPCRs during the fractionation and purification of SMALPs. The overall findings of this study show that the available SMALP protocols can be significantly optimized in several aspects in order to increase the efficiency of GPCR solubilization and isolation from low-yielding expression systems.