Energetics and Dynamics of Lipid Protein Interactions

Dahlquist, Frederick

Abstract

The interaction of lipids and proteins is being investigated using a combination of spectroscopic techniques. The bulk of the proposed work employs specifically deuterated phospholipids and 2H-NMR to examine the interactions. The spectra show the characteristic Pake doublet of a partially disordered liquid crystal and allow determination of the deuterium order parameter which characterizes the motion of the carbon-deuterium bonds under the observation conditions. The deuterium labelled lipids have been reconstituted with bovine mitochondrial cytochrome c oxidase and the deuterium order parameters determined. This demonstrates that the lipid in the reconstituted lipid-protein particles is less ordered than the lipid alone under the same conditions. This result appears to disagree with those obtained by ESR techniques using spin labelled lipid in which protein is observed to further restrict the motion of the lipid. The explanation for these apparently opposite results is not yet clear, but it is likely that the critical issue is the time scale difference of the ESR order measurement and the NMR order measurements. Experiments are proposed to explore these questions. These include (1) covalent attachment of lipid like molecules to protein (2) observation of the spectra of """"""""tightly bound"""""""" lipid (3) rate measurements via saturation transfer in the ESR spectrum of spin labeled lipids (4) detailed examination of T2 relaxation behavior of deuterated lipids and (5) proton spin diffusion rate measurements using isolated proton pairs attached to deuterated lipid and proton containing proteins. These approaches should help to define both the energetic and dynamics of the interaction of lipid and protein.