Multivalent Interactions with Intrinsically Disordered Proteins Probed by Surface Plasmon Resonance.

Multivalent interactions underpin associations between intrinsically disordered proteins (IDPs) and their binding partners. This is a subject of considerable interest and governs how nuclear transport receptors (NTRs) orchestrate the nucleocytoplasmic transport (NCT) of signal-specific cargoes through nuclear pore complexes (NPCs) in eukaryotic cells. Specifically, IDPs termed phenylalanine-glycine nucleoporins (FG Nups) exert multivalent interactions with NTRs to facilitate their transport selectivity and speed through the NPC. Here, we document the use of surface plasmon resonance (SPR) to quantify the affinity and kinetics of NTR-FG Nup binding as a function of FG Nup surface density. Moreover, we describe an in situ method that measures conformational height changes that occur in a FG Nup layer following NTR-binding. Protocols by which the as-obtained SPR results are treated with respect to mass transport limitations are further described. Overall, the SPR methodology described here can be applied to studying multivalent interactions and the role of avidity in diverse biological and biointerfacial systems.