Structure of Membrane-Binding Proteins Revealed by Solid-State NMR

The inside of living cells is separated from the external environment and divided into functionally distinctive compartments by a variety of lipid membranes such as the plasma membrane, the endoplasmic reticulum membrane, the nuclear membrane, etc. Naturally, a number of important cellular functions depend on translocation of materials and transduction of signals between those compartments as results of regulated transports of proteins and small molecules between the membranes of the compartments. In fact, a number of proteins involved in the important cellular functions such as cellular signal transduction, regulation of the cytoskeleton, and regulation of the membrane structure have been known to interact with the membrane surfaces as parts of their functions. Although many of those proteins are classified as water-soluble proteins, important parts of their physiological functions are related to their transient membrane-binding states. In order to understand structure—function relationship of those membrane-binding proteins, the protein structures at the water-lipid bilayer interface should be investigated in detail and compared with those in the aqueous phase, since structural changes accompanying the translocation of the proteins from the aqueous phase to the membrane surface would alter the functions of the proteins at the membrane surfaces where they play important physiological roles.