DeFrND: detergent-free reconstitution into native nanodiscs with designer membrane scaffold peptides.

Membrane scaffold proteins-based nanodiscs (NDs) have facilitated unprecedented structural and biophysical analysis of membrane proteins in a near-native lipid environment. However, successful reconstitution of membrane proteins in NDs requires prior solubilization and purification in detergents, which may impact their physiological structure and function. Furthermore, the detergent-mediated reconstitution of NDs is unlikely to recapitulate the precise composition or asymmetry of native membranes. To circumvent this fundamental limitation of traditional ND technology, we herein describe the development of membrane-solubilizing peptides to directly extract membrane proteins from native cell membranes into nanoscale discoids. By systematically protein engineering and screening, we created a new class of chemically modified Apolipoprotein-A1 mimetic peptides to enable the formation of detergent-free NDs (DeFrNDs) with high efficiency. NDs generated with these engineered membrane scaffold peptides are suitable for obtaining high-resolution structures using single-particle cryo-EM with native lipids. To further highlight the versatility of DeFrNDs, we directly extract a sampling of membrane signaling proteins with their surrounding native membranes for biochemical and biophysical interrogations.