Another major area of research involves the use of solid state NMR techniques to investigate membrane-associated peptides and integral membrane proteins which are receptors for light, hormones, and neurotransmitters. Our strategy involves deuterium labeling of the ligands for integral membrane proteins in conjunction with 2H NMR spectroscopy of membranes aligned on planar substrates. Experimental NMR spectra as a function of tilt angle are simulated using theoretical lineshape models, to obtain the bond angles of the various 2H-labeled groups with respect to the membrane. The angular constraints are then used for molecular modeling of the orientation and conformation of the protein-bound ligand within the membrane. As an initial application, we have recently shown how solid-state 2H NMR spectroscopy can be used to study the retinal chromophore of bacteriorhodopsin, a membrane protein involved in solar energy conversion.
Future work involves extension to other integral membrane proteins and receptors.
In addition, we are engaged in applying solid-state 2H NMR approaches to DNA, which provides a basis for studying the interactions of nucleic acids with drugs, peptides, and proteins. Three-dimensional rendering of two possible orientations of retinal bound to bacteriorhodopsin in the purple membrane as derived from 2H NMR orientational constraints. Molecular Basis of Vision Studied by Fast Photochemical Reaction Techniques. To complement the above NMR studies, we are investigating how equilibrium and dynamical properties of the bilayer lipids influence biological function in the visual system as mediated by the membrane photoreceptor protein rhodopsin. Lipid influences on the photochemistry of rhodopsin in artificial recombinant membranes are studied using rapid kinetic spectrophotometry in real time, together with appropriate kinetic and thermodynamic modeling of the results.