Styrene - Maleic Acid Copolymer 2:1 for Nanodiscs | SMA21

Styrene - maleic acid (SMA) copolymers are broadly used for function and structure studies of membrane proteins. The significant advantages of using SMA copolymers include (1) generating a detergent-free system and (2) forming bilayer nanodiscs with phospholipids. Application of SMA copolymers opens an avenue of membrane protein extraction from cell membranes and proteoliposomes in the absence of detergent. The extracted membrane proteins are stabilized in the nanodiscs that mimic the bilayer structure of lipids in nature. The membrane proteins in nanodiscs can be purified and employed in biochemical, biophysical and biological experiments. For example, the nanodiscs can be used for structure studies of membrane proteins by electronic microscopy (EM). Typically SMA copolymers 2:1 forms nanodiscs in a size about 30 nm while SMA copolymers 3:1 forms nanodiscs in a size about 10 nm. The ideal pH for nanodisc formation is between pH 7.0 – 8.0.

Styrene - Maleic Acid Copolymer 2:1 Free Acid is the free acid form of SMA Copolymer with a molar ratio of styrene to maleic acid of 2:1. The copolymer molecular weight is 10.1 kDa. The free acid form of SMA copolymer is soluble in a pH 8.5 buffer. The package size is 100 mg, 500 mg, 5000 mg and 25 g.
Styrene - Maleic Acid Copolymer 2:1 Sodium Salt is the sodium salt form of SMA copolymer with a molar ratio of styrene to maleic acid of 2:1. The copolymer molecular weight is 10.4 kDa. The salt form of SMA copolymer is soluble in pure water. The package size is 100 mg, 500 mg, 5000 mg and 25 g.

Styrene - Maleic Acid Copolymer 2:1 Solution, pH 7.6 – 10 ml includes 10 ml of 5% Styrene - Maleic Acid Copolymer 2:1 in 0.1 M Tris-HCl, pH 7.6.
Preparation of 5% SMA copolymer stock solution from the solid polymer
A convenient way to make nanodiscs is to use a stock solution of 5 % SMA copolymer. The pH is adjusted to 7.6 which is optimal for nanodisc formation. The solution is filtrated through a 0.8 um filter and stored in a 4ºC refrigerator or -20 ºC freezer. Note: The buffer used for SMA copolymer nanodiscs should be between pH 6 – 9, preferably pH 7 – 8. A lower pH will result in precipitation of the copolymer and a higher pH will destabilize the nanodisc structure.
Formation of nanodiscs from cell membranes
Incubate 15 mg of cell membrane in 5 ml of 50 mM Tris-HCl, pH 7.6, 0.5 M NaCl, and 10 % glycerol with 5 ml of 5 % SMA copolymer, pH 7.6 by gentle agitation at room temperature overnight.
Formation of nanodiscs from Proteoliposomes
Incubate proteoliposomes composed of 15 mg of lipids and reconstituted membrane proteins in 5 ml of 50 mM Tris-HCl, pH 7.6, 0.5 M NaCl, and 10 % glycerol with 5 ml of 5 % SMA copolymer, pH 7.6 by gentle agitation at room temperature overnight.
Purification of nanodiscs
Nanodiscs can be dialyzed using dialysis membranes to remove small molecules and concentrated by ultrafiltration. Size exclusion chromatography (SEC) can be employed for purification of nanodiscs

Protein purification
SEC or affinity column chromatography can be employed for membrane protein purification of the discoidal membrane proteins. However, complete solubilization with a proper detergent to the size of molecular level is often required to gain high purity proteins. The chromatographically purified proteins in detergent micelles are reconstituted in liposomes or nanodiscs.