Alternatives to Styrene- and Diisobutylene-Based Copolymers for Membrane Protein Solubilization via Nanodisc Formation

Styrene-maleic acid copolymers (SMAs), and related amphiphilic copolymers, are promising tools for isolating and studying integral membrane proteins in a native-like state. However, they do not exhibit this ability universally, as several reports have found that SMAs and related amphiphilic copolymers show little to no efficiency when extracting specific membrane proteins. Recently, it was discovered that esterified SMAs could enhance the selective extraction of trimeric Photosystem I from the thylakoid membranes of thermophilic cyanobacteria; however, these polymers are susceptible to saponification that can result from harsh preparation or storage conditions. To address this concern, we herein describe the development of & alpha;-olefin-maleic acid copolymers (& alpha;MAs) that can extract trimeric PSI from cyanobacterial membranes with the highest extraction efficiencies observed when using any amphiphilic copolymers, including diisobutylene-co-maleic acid (DIBMA) and functionalized SMA samples. Furthermore, we will show that & alpha;MAs facilitate the formation of photosystem I-containing nanodiscs that retain an annulus of native lipids and a native-like activity. We also highlight how & alpha;MAs provide an agile, tailorable synthetic platform that enables fine-tuning hydrophobicity, controllable molar mass, and consistent monomer incorporation while overcoming shortcomings of prior amphiphilic copolymers. Styrene- and diisobutylene-based amphiphilic copolymers are invaluable tools for the extraction of integral membrane proteins. However, they have several issues that limit their efficacy and applicability. A tailorable polymeric platform is now introduced that overcomes many of these limitations, including having low UV absorbance, high protein extraction yields, and retention of native-like protein structure, as well as being readily synthesized.image

Automated summary

Styrene-maleic acid copolymers and related amphiphilic copolymers are promising tools for isolating and studying integral membrane proteins. A new polymeric platform is introduced in this study, which overcomes limitations of existing copolymers and offers advantages such as low UV absorbance, high protein extraction yields, and retention of native-like protein structure.