STRUCTURE-FUNCTION OF RHODOPSIN-LIPID MEMBRANES

In broad terms, our goal is to determine the molecular nature of
membrane-related events which underly visual excitation in the rod cells of
the vertebrate retina. The most immediate objectives of this proposal can
be specifically grouped as follows: (i) Chemical synthesis, isotopic labelling with 2H, and structural studies
employing nuclear magnetic resonance (NMR) of highly polyunsaturated
phospholipids. Such polyunsaturated phospholipids are found in extremely
high levels in the vertebrate retinal rod outer segment (ROS) disk
membranes; yet, little is known of their structural or functional
properties. It is possible that such polyunsaturated phospholipids may
play a specific but as yet undertermined role in the process of vision. (ii) Application and development of new solid-state NMR techniques for
structural studies of phospholipid bilayers. High-resolution solid-state
13C NMR spectra will be obtained and new NMR relaxation methods will be
developed to obtain information regarding the orientational ordering and
molecular dynamics of phospholipids in both native and recombinant
membranes containing rhodopsin. (iii) The photochemical function of rhodopsin in recombinant membranes will
be studied using flash photolysis techniques as well as recently developed
enzymatic assays. The role of structural variables such as the
phospholipid acyl chain length and the degree and position of the acyl
chain unsaturation on the function of rhodopsin will be systematically
investigated. Using these methods, and following the approach outlined in this proposal,
it is our intent to provide a fairly complete physical picture of
rhodopsin-lipid interactions and their relationship to function during the
proposed RCDA project period. Throughout this work, emphasis will be
placed upon correlation of the structural properties of the
rhodopsion-containing membranes with selected aspects of their
vision-related function.