Nanodiscs in Membrane Biochemistry and Biophysics

Abstract

Membrane proteins play a most important part in metabolism, signaling, cell motility, transport, development, and many other biochemical and biophysical processes which constitute fundamentals of life on the molecular level. Detailed understanding of these processes is necessary for the progress of life sciences and biomedical applications. Nanodiscs provide a new and powerful tool for a broad spectrum of biochemical and biophysical studies of membrane proteins and are commonly acknowledged as an optimal membrane mimetic system that provides control over size, composition, and specific functional modifications on the nanometer scale. In this review we attempted to combine a comprehensive list of various applications of nanodisc technology with systematic analysis of the most attractive features of this system and advantages provided by nanodiscs for structural and mechanistic studies of membrane proteins.

Figure 1

Nanodiscs are discoidal lipid bilayer stabilized by encircling amphipathic helical scaffold proteins termed MSPs.

Figure 2

Schematic descriptions of the self-assembly process where detergent solubilized target, lipid and membrane scaffold protein yield Nanodiscs upon removal of detergent.

Figure 3

A Soluble Membrane Protein Library (SMPL) can be generated wherein membrane proteins can be directly assembled into Nanodiscs from intact tissue.

Figure 4

Schematic illustration of MSP sequences described in Table 1, and designed by Wagner et al. MSP1D1 and extended scaffold proteins with several N-terminal affinity tags, as well as C-terminal modifications with biotin and FLAG-tag are available. Truncated MSP proteins form smaller Nanodiscs and are especially useful for enhanced mobility and improved resolution of NMR spectra of incorporated membrane proteins.

Figure 5

The experimentally determined number of optimally assembled lipids in Nanodiscs (N), either DPPC (circles) or POPC (triangles), is correlated with the number of residues (M) in the encircling scaffold proteins. This demonstrated that the first portion of Helix 1 was not involved key protein-lipid interactions. See Equation 1, Table I and Figure 4.

Figure 6

Lipid packing in small Nanodiscs (27 lipids and 123 amino acids MSP) and the regular Nanodiscs sized (60 lipids, 189 amino acids in MSP1D1). Boundary lipids interacting with MSP are marked with dots. See text for discussion.

Figure 7

Molecular Dynamics Simulations of DPPC Nanodiscs with incorporated bR monomer.

Figure 8

The structure of the ryanodyne receptor in Nanodiscs as determined by cryo-electron microscopy.

Figure 9

The structure of the membrane protein OmpX in Nanodiscs is determined by solution NMR spectroscopy.

Figure 10

Schematic representation of the bacteria chemotactic receptor Tar in Nanodiscs illustrating the CheA kinase dimer, AA’, and the coupling protein, CheW. A trimer of Tar dimers are incorporated in separate Nanodiscs and interact to form a fully functional unit.