A comparison of SMA (styrene maleic acid) and DIBMA (di-isobutylene maleic acid) for membrane protein purification

Abstract

The use of styrene maleic acid co-polymer (SMA) for membrane protein extraction and purification has grown in recent years. SMA inserts in the membrane and assembles into small discs of bilayer encircled by polymer, termed SMA lipid particles (SMALPs). This allows purification of membrane proteins whilst maintaining their lipid bilayer environment. SMALPs offer several improvements over conventional detergent approaches, however there are limitations, most notably a sensitivity to low pH and divalent cations. Recently it was shown that the aliphatic diisobutylene-maleic acid (DIBMA) copolymer, was also able to directly solubilize membranes forming DIBMALPs (DIBMA lipid particles), and that this polymer overcame some of the limitations of SMA. In this study the ability of DIBMA to solubilize and purify functional membrane proteins has been compared to SMA. It was found that DIBMA is able to solubilize several different membrane proteins from different expression systems, however for some proteins it gives a lower yield and lower degree of purity than SMA. DIBMA extracted G protein-coupled receptors retain ligand-and G proteinbinding. DIBMALPS are larger than SMALPs and display a decreased sensitivity to magnesium. However the stability of DIBMALPs appears to be lower than SMALPs. The lower purity and lower stability are likely linked to the larger size of the DIBMALP particle. However, this also offers a potentially less rigid lipid environment which may be more amenable to protein dynamics. Therefore the optimal choice of polymer will depend on which features of a protein are to be investigated.

Lipid Nanodiscs via Ordered Copolymers

“…This is further complicated by the observation that polymer extraction is largely protein and lipid dependent, with nanodisc-forming polymers being equal, more, or less effective than the detergent, dependent on the system. [31][32][33][34][35]58,59 Polymers for which there exists comparisons of extraction efficacies to SMA2000 are outlined in Table S1, in addition to known limitations in buffer compatibilities and divalent cations. In this study, we assessed the efficacy of AASTY polymers with fluorescent sizeexclusion chromatography (FSEC), using HEK293F cells recombinantly overexpressing the human transient receptor potential melastatin type 4 (hTRPM4) fused with an N-terminal StrepTagII and a green fluorescent protein (GFP) tag as our test system (Figure 2A).…”

Capturing Membrane Protein Ribosome Nascent Chain Complexes in a Native-like Environment for Co-translational Studies

“…Lyophilized DIBMA stocks were quality checked 39 using a Shimadzu IR Affinity-1s or a PerkinElmer Spectrum Two FTIR instrument, scanned across a complete wavenumber range of 4000–400 cm –1 , with 16 scans to measure transmittance ( Figure S3a ). In particular, the carboxylate (1705 cm –1 ) and anhydride (1775 cm –1 ) bands were checked to ensure that our treatment of the polymer with strong acids did not result in a condensation of the anhydride ring, which would result in a significantly reduced solubilization efficiency.…”

Structures of ABC transporters: handle with care

“…A recent low-resolution cryogenic electron microscopy (cryo-EM) analysis of MalEFGK 2 was conducted in nanodiscs and could provide a basis for future useful mechanistic investigations [41]. Alternatively, investigation of other detergent alternatives [42,43] may also be helpful for future structural studies.…”