Distance measurements and conformational analysis of sn-2- arachidonoylglycerol-membrane sample by 2H-31P REDOR NMR

Abstract

The purpose of these studies is to determine the intermolecular distances that define the location, orientation, and conformation of 2-AG in palmitoyl-oleoyl-phosphatidylcholine (POPC) lipid bilayers using rotational-echo double-resonance (REDOR) NMR. All five protons on the glycerol backbone of 2-AG were replaced with 2H and the distance between the deuterons and naturally occurring 31P on the POPC lipid headgroup determined with REDOR. To determine the distance from each deuteron to the phosphorus, the POPC headgroup was arranged in a hexagonal array. The 2-AG intercalates between the lipid molecules and the 2H labels, resulting in an average distance of z directly above or below the center of the parallelogram of the four phosphorus atoms P1, P2, P3, and P4. For different z values, the 2H-31P inter-nuclear distances were 7.6-9.1 Å (2H-31P1 and 2H-31P31) and 4.4-6.7 Å ( 2H-31P2 and 2H-31P 4). Each result involved the calculations and summation of 893,101 terms. Based on the curve-fitting parameters, the calculations with z = 0 fits the data the best, which means these methylene 2H atoms are at the same level as the phosphate group of the POPC lipid bilayer. Molecular dynamic simulation data suggested that the 2H atoms at the glycerol backbone of 2-AG are involved in an extended H-bonding network with the phosphorus atoms after 10-ns simulation. © 2014 Springer Science+Business Media.