Elucidating the link between structure and function of ion channels and transporters with voltage-clamp and patch- clamp fluorometry

Abstract

Ion channels and transporters are membrane proteins whose functions are driven by conformational changes. This implies that to gain a deep understanding of their dynamic behavior, structural and functional information need to be integrated. Classical biophysical techniques provide insight into either the structure or the function of these proteins, but their correlation in time remains a challenging task. In this chapter, we illustrate how two related techniques, voltage-clamp fluorometry (VCF) and patch-clamp fluorometry (PCF), provide such a type of integrated information. They combine electrophysiological techniques, two-electrode voltage-clamp (VCF) and patch-clamp (PCF), with spectroscopic approaches to simultaneously detect conformational changes and ionic currents mediated by ion channels and transporters in a native membrane environment. The optical part is based on the environmental sensitivity of the fluorescence emission of probes attached at specific sites of ion channels and transporters. This allows the correlation between structural conformation and defined functional states. VCF and PCF have been applied to a variety of ion channel and transporter families to investigate several biophysical problems ranging from structural changes linked to activation by various stimuli to the analysis of the process of inactivation and deactivation. Additionally, these techniques allowed for reading out gating-dependent ligand binding and protein mobility. In this chapter, illustrating some typical examples of the application of VCF and PCF, we try to show their potential and flexibility and to highlight some of the technical caveats.