Influence of Poly(styrene-co-maleic acid) Copolymer Structure on the Properties and Self-Assembly of SMALP Nanodiscs

Abstract

Polymer stabilized nanodiscs are self-assembled structures composed of a polymer belt that wraps around a segment of lipid bilayer, and as such are capable of encapsulating membrane proteins directly from the cell membrane. To date, most studies on these nanodiscs have used poly(styrene- co-maleic acid) (SMA) with the term SMA-lipid particles (SMALPs) coined to describe them. In this study, we have determined the physical and thermodynamic properties of such nanodiscs made with two different SMA copolymers. These include a widely used and commercially available statistical poly(styrene- co-maleic acid) copolymer (coSMA) and a reversible addition-fragmentation chain transfer synthesized copolymer with narrow molecular weight distribution and alternating styrene and maleic acid groups with a polystyrene tail, (altSMA). We define phase diagrams for each polymer, and show that, regardless of polymer topological structure, self-assembly is driven by the free energy change associated with the polymers. We also show that nanodisc size is polymer dependent, but can be modified by varying polymer concentration. The thermal stability of each nanodisc type is similar, and both can effectively solubilize proteins from the E. coli membrane. These data show the potential for the development of different SMA polymers with controllable properties to produce nanodiscs that can be optimized for specific applications and will enable more optimized and widespread use of the SMA-based nanodiscs in membrane protein research.

An acid-compatible co-polymer for the solubilization of membranes and proteins into lipid bilayer-containing nanoparticles

“…Below the saturation boundary, a large z -average diameter was observed. This agrees well with 31 P-NMR data discussed above, and with previous reports using the SMA(2 : 1), 33 , 34 SMA(3 : 1) 21 , 37 and DIBMA 40 polymers. As polymer concentration increases beyond the SAT boundary, a rapid decrease of z -average diameter and polydispersity index (PDI) is observed ( Fig.…”

“…The commonly used variants of the SMA polymer have now been investigated thoroughly 21 , 33 – 39 showing that the first used polymer (SMA2000) is the best performing of the polymers so far studied. However, SMA has its limitations.…”

Non-detergent isolation of a cyanobacterial photosystem I using styrene maleic acid alternating copolymers

“…The requirement for 100-500 mM monovalent ions to facilitate protein extraction using SMA copolymers has previously been reported in the literature. [48][49][50][51] Our results corroborate these ndings showing an increase in PSI extracted as concentrations of KCl ( Fig. 2D) and NaCl ( Fig.…”

Examining the stability of membrane proteins within SMALPs

“…Previous studies on the thermodynamics of phospholipid solubilisation by SMA2000 [27] and SZ30010 [24] indicate that these polymers have similar thermodynamic efficiencies. SMA2000 exhibits a larger negative free energy change associated with the polymer, indicating it is more efficient at solubilising phospholipids.…”