Nanodisc-reconstitution for single particle cryo-EM structure determination of membrane proteins

Reconstitution of membrane proteins in nanodiscs has proven to be a highly effective approach to study membrane protein structures in a lipid bilayer, resulting in many recent single particle cryo-EM structures. While most of these studies employed membrane scaffold protein (MSP) nanodiscs, additional types of nanodiscs were developed based on MSPs and provide alternative approaches. Nanodiscs have been particularly effective in solving structures of different protein conformations and of bound lipids, demonstrating key roles of specific lipids in structural integrity and protein function. At the same time, discrepancies of lipid behavior in nanodiscs compared to native membranes and liposomes necessitate careful scrutiny of reconstitution parameters and further evaluation. This brief review covers an overview of types of nanodiscs currently in use for cryo-EM structural studies, their advantages and limitations, as well as examples of the dramatically increased understanding they can reveal.