Very fruitful collaboration between French and German scientists yields unusual insights into the structure of membrane proteins Scientists from the Max Planck Institute of Biochemistry in Martinsried, Germany, and the Institute of Structural Biology in Grenoble, France, used neutron beams to expand current knowledge on structure-function relations in the ion pump bacteriorhodopsin. By using isotope-labeled membranes, areas of different dynamical behavior were detected, and a functionally essential Glycolipid was localized. Using neutron spectroscopy and diffraction experiments, which are sensitive to isotope labels, areas of differential dynamical behavior within the protein, as well as the position of functionally important lipids surrounding it, were localized.
Membrane proteins play key roles in the functioning of the living cell.
Apart from very few exceptions, their structure-function relations, however, still remain unclear. Biological activity in proteins is correlated with this transition, suggesting that this type of flexibility is a prerequisite for function. The thermal motions of the labeled atoms in the heart of the protein, however, demonstrate stiffer behavior and, at room temperature, they have significantly smaller amplitudes of motion. Contrary to the bulk mean behavior, they appear to be shielded from solvent melting effects. These experimental results quantify the dynamical heterogeneity of bacteriorhodopsin, which meets the functional requirements of bulk flexibility, on the one hand, to allow large conformational changes in the molecule, and of a harder core, on the other, to control stereo-specific conformation changes of the central retinal.