Tailoring Butyl Methacrylate/Methacrylic Acid Copolymers for the Solubilization of Membrane Proteins: The Influence of Composition and Molecular Weight

Abstract

Low‐molecular weight (MW) amphiphilic copolymers have been recently introduced as a powerful tool for the detergent‐free isolation of cell membrane proteins. Herein, a screening approach is used to identify a new copolymer type for this application. Via a two‐step ATRP/acidolysis procedure, a 3 × 3 matrix of well‐defined poly[(butyl methacrylate)‐co‐(methacrylic acid)] copolymers (denoted BMAA) differing in their MW and ratio of hydrophobic (BMA) and hydrophilic (MAA) units is prepared. Subsequently, using the biologically relevant model (T‐cell line Jurkat), two compositions of BMAA copolymers are identified that solubilize cell membranes to an extent comparable to the industry standard, styrene‐maleic acid copolymer (SMA), while avoiding the potentially problematic phenyl groups. Surprisingly, while only the lowest‐MW variant of the BMA/MAA 2:1 composition is effective, all the copolymers of the BMA/MAA 1:1 composition are found to solubilize the model membranes, including the high‐MW variant (MW of 14 000). Importantly, the density gradient ultracentrifugation/sodium dodecyl sulfate‐polyacrylamide gel electrophoresis/Western blotting experiments reveal that the BMA/MAA 1:1 copolymers disintegrate the Jurkat membranes differently than SMA, as demonstrated by the different distribution patterns of two tested membrane protein markers. This makes the BMAA copolymers a useful tool for studies on membrane microdomains differing in their composition and resistance to membrane‐disintegrating polymers.

Novel class of peptides disintegrating biological membranes to aid in the characterization of membrane proteins

“…In our recent studies, we used SMA to characterize membrane proteins present within and outside of membrane rafts in T cells and other cell types ( 7 , 15 ). We also demonstrated similar membrane-disintegrating properties of other amphiphilic copolymers ( 8 , 16 ).…”

“…These nanodiscs, also called SMA-lipid particles, are relatively stable and do not need the presence of a free soluble copolymer in the solution. Similar to detergents, the membrane raft–associated proteins are not fully solubilized by SMA or other similar copolymers and remain in larger copolymer-resistant membrane fragments ( 7 , 8 ). The proteins contained in the nanodiscs thus behave essentially like soluble (lipo)proteins.…”