A neutron diffraction study of the headgroup conformation of phosphatidylglycerol from Escherichia coli membranes

By using neutron diffraction, the headgroup conformation of purified phosphatidylglycerol from Escherichia coli membranes has been investigated. Measurements at 25 degrees C and 15% relative humidity on oriented multilayers of lipid selectively deuterated at the sn-3-position of the glycerol backbone and of the gamma-position of the glycerol headgroup show that the labels are at a mean distance of 23.0 A and 27.6 A from the centre of the hydrocarbon chain region. This suggests that the negatively charged headgroup is oriented at about 30 degrees to the membrane surface. The orientation of the phosphatidylglycerol headgroup makes the negatively charged phosphate group easily accessible to cations present in the adjacent water layer.