Magnetic Resonance Spectroscopic Studies of the Integral Membrane Protein Phospholamban

Membrane proteins (which make up approximately one-third of the total number of known proteins) are responsible for many important properties and functions of biological systems: they transport ions and molecules across the membrane, they act as receptors, and they have roles in the assembly, fusion, and structure of cells and viruses. Despite the abundance and clear importance of membrane-associated molecules, very little information about these systems exists. A plethora of membrane proteins are intimately associated with cardiovascular function and disease. Structural studies of these membrane proteins represent one of the final frontiers in structural biology. X-ray crystallography is the premiere technique that is used to elucidate structural information of biologically significant protein systems. However, this technique has not been very successful in providing structural information about membrane protein systems. The hydrophobic surfaces associated with membrane-bound protein systems make the crystallization process extremely difficult. Although researchers are making progress with X-ray techniques, still only a handful of membrane protein structures have been obtained via X-ray crystallography [1–5]. Alternatively, solution NMR spectroscopy, solid-state NMR spectroscopy, and EPR spectroscopy are powerful techniques that can be used to provide structural, orientational, and dynamic information about membrane protein systems in lipid bilayers [6–10]. This short review chapter will analyze some of the magnetic resonance techniques that have been used to investigate the integral membrane protein phospholamban (PLB).