SMA-PAGE: a new method to examine complexes of membrane proteins using SMALP nano-encapsulation and native gel electrophoresis

Most membrane proteins function through interactions with other proteins in the phospholipid bilayer, the cytosol or the extracellular milieu. Understanding the molecular basis of these interactions is key to understanding membrane protein function and dysfunction. Here we demonstrate for the first time how a nano-encapsulation method based on styrene maleic acid lipid particles (SMALPs) can be used in combination with native gel electrophoresis to separate membrane protein complexes in their native state. Using four model proteins, we show that this separation method provides an excellent measure of protein quaternary structure, and that the lipid environment surrounding the protein(s) can be probed using mass spectrometry. We also show that the method is complementary to immunoblotting. Finally we show that intact membrane protein-SMALPs extracted from a band on a gel could be visualised using electron microscopy (EM). Taken together these results provide a novel and elegant method for investigating membrane protein complexes in a native state.