Structural Transitions in Membrane Proteins Revealed by Infrared Reflection Absorption Spectroscopy

Abstract

Infrared Reflection Absorption Spectroscopy (IRRAS) is a versatile technique to study the organization of interfacial films on a molecular or even sub-molecular level, such as lipid monolayers including peripheral membrane proteins. IRRAS combines the film balance technique with IR reflectivity and spectroscopy, which provides structural information, reveals the presence of molecules, their interactions, their conformation and their phase state. In addition, and in contrast to solution IR spectroscopy the orientation of molecules or molecular moieties at the interface can be determined by IRRAS. We will present examples for the value of IRRAS in studying lipid - protein interactions. Such, it was used to determine conformation and orientation in which fusion peptides bind to lipid membranes [1]. Furthermore, the orientations of the ATPase Sar1 in its membrane bound state could be determined with implications on the mechanism of the COPII coat assembly [2]. And even structural rearrangements within large proteins (the dynamin EHD2) during the membrane binding process [3] were revealed in nearly natural conditions, i.e. physiological temperature, desired buffer composition and low protein concentration. [1] M. Rabe et al., Langmuir, 2014, 30, 7727 [2] C. Schwieger et al., Polymers 2017, 9, 612 [3] M. Hoernke et al., PNAS, 2017, 214 (22), E4360