Surface plasmon resonance biosensing in studies of the binding between β₂ integrin I domains and their ligands

Measurements on the kinetic aspects of binding between macromolecular species such as proteins have been greatly advanced by the application of surface plasmon resonance (SPR) biosensors. In studies of ligand binding by integrin I domains, technologies such as the BIAcore instruments have provided important insights into the role of conformational regulation. This chapter describes a protocol for studying the binding between the I domain from integrin α(X)β(2) and its ligand iC3b. Also included are topics on the interpretation of data. Integrin I domains appear to support heterogeneous interactions with ligands, which pose significant challenges in deriving valid information on the binding kinetics from the SPR measurements. Fortunately, new algorithms are available that may resolve even complex ligand-binding reactions; with the application to data on the binding between the α(X) I domain, a more consistent and unambiguous result is obtained compared to those obtained by classical approaches for analyzing SPR biosensor data.