Heterogeneous Systems Membrane Proteins

Structural as well as dynamical studies of membrane proteins, constituting an estimated 30% of all proteins, are very important in view of their crucial biological importance. These membrane proteins are obviously dynamically heterogeneous systems, even though they are structurally homogeneous without any cross-links or aggregation so far discussed. 

Indeed, hydrophilic N- or C-terminal ends and loop domains of these membrane proteins exposed to aqueous phases are able to undergo rapid or intermediate motional fluctuations, respectively, as shown in the 3D pictures of transmembrane (TM) moieties of bacteriorhodopsin (bR) as a typical membrane protein in the purple membrane (PM) of Halobacterium salinarum.176 178 Structural information about protein surfaces, including the interhelical loops and N- and C-terminal ends, is completely missing from X-ray data. It is also conceivable that such pictures should be further modified, when membrane proteins in biologically active states are not always present as oligomers such as dimer or trimer as in 2D or 3D crystals but as monomers in lipid bilayers. 

---

Key Words Structurally and/or dynamically heterogeneous systems, Hydrogels, Protein fibrils, Membrane proteins, Dynamic aspects... 

We have emphasized here that the dynamic aspects of NMR studies are crucially important for structurally or dynamically heterogeneous systems such as synthetic or natural hydrogels, protein fibrils and membrane proteins. This is in order to characterize their unique chemical, physical and biological properties in terms of a variety of fluctuation frequencies, including high (> 108 Hz) or intermediate (104-105 Hz) frequency fluctuations. It turns out that the presence of the high-frequency motions, which are readily evaluated by comparative CPMAS and DDMAS studies, is... 

H. Saito, NMR studies on structurally or dynamically heterogeneous systems dynamic aspects of hydrogels, protein fibrils and membrane proteins, Annu. Rep. NMR Spectrosc. 74 (2011) 1-88. 

Our work deals with the necessity of creating kinetics laws for heterogeneous enzymology. There was a big gap between the classical enzyme kinetics in solution and highly structured biological systems. All the concepts of diffusion reaction are clear for our thick membrane but are also useful for lipid-protein membranes, even if the process of transport is not only classical diffusion. 

---