Abstract
Membrane proteins possess a variety of functions essential to the survival of organisms. However, due to their inherent hydrophobic nature, it is extremely difficult to probe the structure and dynamic properties of membrane proteins using traditional biophysical techniques, particularly in their native environments. Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) is a very powerful and rapidly growing biophysical technique to study pertinent structural and dynamic properties of membrane proteins with no size restrictions. In this review, we will briefly discuss the most commonly used EPR techniques and their recent applications for answering structure and conformational dynamics related questions of important membrane protein systems.
Highlights
Membrane proteins contribute less than 2% of the structure in the protein data bank (PDB) [11,14,15]
This study further revealed that the use of the nanodiscs (NDs) provided improvement in the overall signal-to-noise ratio (S/R) of double electron electron resonance (DEER) signals and increased the resolution in the distance distribution [155]
DEER distance measurements on 188R1-399R1 cells showed a shorter distance in the apo-state in E. coli when compared to that in the presence of Ca2+ or CN-Cbl, suggesting conformation changes induced by ligand binding [179]
Summary
Understanding the basic characteristics of a membrane protein is very important to knowing its biological significance. The knowledge of structural dynamics and functions of membrane proteins is of high biological importance [11,12,13]. Membrane proteins are difficult to crystallize as they are solubilized in detergent/lipids and have high hydrophobicity [18,20] This introduces challenges for X-ray crystallographic techniques for studying many membrane proteins [25]. Nuclear magnetic resonance spectroscopy (NMR) is used to obtain both structural and dynamics information of a variety of membrane proteins in a non-crystal environment. FRET is a good technique to monitor the conformational changes for individual membrane protein systems This technique may cause higher structural perturbation due to the presence of relatively larger probe sizes. EPR spectroscopy is a powerful biophysical technique that minimizes these limitations and provides pertinent structural and dynamic information about membrane proteins
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