Controlling Styrene Maleic Acid Lipid Particles through RAFT

Abstract

The ability of styrene maleic acid copolymers to dissolve lipid membranes into nanosized lipid particles is a facile method of obtaining membrane proteins in solubilized lipid discs while conserving part of their native lipid environment. While the currently used copolymers can readily extract membrane proteins in native nanodiscs, their highly disperse composition is likely to influence the dispersity of the discs as well as the extraction efficiency. In this study, reversible addition-fragmentation chain transfer was used to control the polymer architecture and dispersity of molecular weights with a high-precision. Based on Monte Carlo simulations of the polymerizations, the monomer composition was predicted and allowed a structure-function analysis of the polymer architecture, in relation to their ability to assemble into lipid nanoparticles. We show that a higher degree of control of the polymer architecture generates more homogeneous samples. We hypothesize that low dispersity copolymers, with control of polymer architecture are an ideal framework for the rational design of polymers for customized isolation and characterization of integral membrane proteins in native lipid bilayer systems.

The Peptidisc, a simple method for stabilizing membrane proteins in detergent-free solution

“…This is because peptide synthesis is sequential, whereas addition of carboxylate and other repeating units in amphipols and industrially prepared SMA polymers is randomly distributed along the polymer chain during assembly. Due to the ‘one-pot’ synthesis, these synthetic polymer preparations are often polydisperse mixtures of different lengths ( Popot, 2010 ; Smith et al, 2017 ). This compositional heterogeneity can be problematic for functional and structural studies ( Deller et al, 2016 ).…”

Characterizing the structure of styrene-maleic acid copolymer-lipid nanoparticles (SMALPs) using RAFT polymerization for membrane protein spectroscopic studies

“…Recently, our lab has shown that 3:1 styrene-maleic acid can be synthesized in a laboratory setting using reversible addition-fragmentation chain transfer polymerization (RAFT) polymerization and successfully used to characterize the structure of styrene-maleic acid copolymerlipid nanoparticles (SMALPs) 15,30 . RAFT polymerization is synthetically simple and provides flexibility to vary the structure of the polymer and influence the size of SMALPs 15,30 . SMALPs show compelling evidence that they are suitable for membrane protein incorporation 15 .…”

Membrane biology visualized in nanometer-sized discs formed by styrene maleic acid polymers

“…This analysis indicates that RAFT-SMA with alternating 3:1 subunit ratios are optimal for rapid and complete dissolution of synthetic liposomes into small discs, while larger protein complexes may be better solubilized by RAFT-SMA(2:1) polymers. A recent study of RAFT polymerization shows that greatest solubilization is achieved using a steep gradient of styrene and maleic acid monomers in a small (3kDa) polymer, while inclusion of a long homoblock of styrene is detrimental [20]. …”