SMPL synaptic membranes: Nanodisc-mediated synaptic membrane mimetics expand the toolkit for drug discovery and the molecular cell biology of synapses

We describe in detail how proteins of synaptic membranes can be extracted and reconstituted within “Nanodiscs” which renders them soluble in aqueous solutions. Each Nanodisc is a nanometer-scaled lipid bilayer containing an individual membrane protein. The method can provide a soluble membrane protein library (SMPL) from any tissue fraction, notably from the standpoint of this treatise, from synaptosome plasma membranes (SMPL synaptic membranes). Nanodiscs facilitate investigations of membrane proteins that are difficult to tease apart from protein-protein complexes while at the same time maintaining conformational integrity. The procedure captures virtually all membrane proteins in a manner that preserves their activities in soluble form. The usefulness of SMPL synaptic membranes is exemplified by experiments that concern the specific binding of Alzheimer’s-related amyloid β oligomers (AβOs). AβO binding to SMPL synaptic membranes is saturable, has the same high affinity found in cell-based assays, and is mediated adventitiously by particular proteins. Immunoaffinity isolation experiments have identified one AβO toxin “receptor” as the NaK ATPase α3 (NKAα3). For drug discovery, recombinant membrane proteins in Nanodiscs can be readily coupled to high-throughput screening platforms; SMPL synaptic membranes can also be readily coupled and used for unbiased high-throughput screening of unknown targets. SMPL synaptic membranes, and analogous organelle libraries, offer new resources for the CNS membrane protein toolkit with a wide array of applications to synapse molecular cell biology and drug discovery.