Membrane-SPINE: a biochemical tool to identify protein-protein interactions of membrane proteins in vivo

Membrane proteins are essential for cell viability and are therefore important therapeutic targets(1-3). Since they function in complexes(4), methods to identify and characterize their interactions are necessary(5). To this end, we developed the Membrane Strep-protein interaction experiment, called Membrane-SPINE(6). This technique combines in vivo cross-linking using the reversible cross-linker formaldehyde with affinity purification of a Strep-tagged membrane bait protein. During the procedure, cross-linked prey proteins are co-purified with the membrane bait protein and subsequently separated by boiling. Hence, two major tasks can be executed when analyzing protein-protein interactions (PPIs) of membrane proteins using Membrane-

first, the confirmation of a proposed interaction partner by immunoblotting, and second, the identification of new interaction partners by mass spectrometry analysis. Moreover, even low affinity, transient PPIs are detectable by this technique. Finally, Membrane-SPINE is adaptable to almost any cell type, making it applicable as a powerful screening tool to identify PPIs of membrane proteins.