Abstract
Over the past decade, Styrene Maleic Acid alternating copolymers (SMA) have gained interest as an alternative to detergent solubilization for the isolation of integral membrane proteins. The formation of SMA lipid particles (SMALPs) presents a novel opportunity to isolate the proximal membrane environment, encompassing and throughout membrane proteins in vitro. Neither the organization or structure of SMAs in an aqueous buffer nor the mechanism by which SMA transforms the membrane bilayer into a SMALP is known. This study investigates the shape and size of diverse SMA polymer complexes/aggregates in solution at various pH, ionic strength, SMA concentration and temperature, analyzed by small angle X-ray scattering. It is clear that SMAs of differing physicochemical properties (styrene to maleic acid ratio, length of copolymer fragments and functionalization) display highly variable sizes/shapes in solution over a range of environmental conditions. The SMA supramolecular aggregates exhibit similar prolate ellipsoidal geometry of varying size, dependent on the degree of hydrophobicity of the SMA copolymer. At elevated temperature, particles composed of SMAs enriched in styrene increase in both radius of gyration and maximum particle diameter. Interestingly, we observe a correlation between the SMALP dimensions and that of native membranes. Future work will investigate if there may be a complimentary relationship between SMA aggregate dimensions and bilayer thickness (and/or protein transmembrane domain thickness), similar to what has been observed for tandem facial amphiphiles.
| Original language | English |
|---|---|
| Pages (from-to) | 178-184 |
| Number of pages | 7 |
| Journal | European Polymer Journal |
| Volume | 111 |
| DOIs | |
| State | Published - Feb 2019 |
Funding
We thank Stefan Scheidelaar and Pieter Hanssen from Polyscope Polymers, Geleen, The Netherlands, for providing SMA copolymers and their support to our research and the SMALP community. We also thank Bill Dougherty from Cray Valley, Exton, Pennsylvania, USA for providing SMA copolymer samples used in this work. The materials and technical expertise allowed us from these two companies allows this work to be possible. We would also like to thank Dr. Olena Korotych for her critical review of this manuscript, and aid in interpretation of these results. SAXS measurements were supported by DOE scientific user facilities at ORNL. Funding for CSMB is provided by the Office of Biological & Environmental Research in the Department of Energy’s Office of Science . Support to B.D.B. and N.G.B. has been provided from the Gibson Family Foundation , the UTK/ORNL Science Alliance, the Tennessee Plant Research Center, JDRD Award to B.D.B., the Dr. Donald L. Akers Faculty Enrichment Fellowship to B.D.B. and National Science Foundation support to B.D.B. ( DGE-0801470 and EPS-1004083 ). N.G.B. was also supported by the Penley Foundation Fellowship. Access to SAXS at ORNL was supported by a HIFR Beam Time Award 20149. These funding sources were not involved in data collection, analysis, interpretation or report writing.
Keywords
- Amphiphilic polymer
- Membrane protein solubilization
- Small angle X-ray scattering (SAXS)
- Styrene maleic acid (SMA)
- Styrene maleic acid lipid particle (SMALP)
- Supramolecular assembly