Phospholipid headgroups govern area per lipid and emergent elastic properties of bilayers.

Phospholipid bilayers are liquid-crystalline materials whose intermolecular interactions at mesoscopic length scales have key roles in the emergence of membrane physical properties. Here we investigated the combined effects of phospholipid polar headgroups and acyl chains on biophysical functions of membranes with solid-state H NMR spectroscopy. We compared the structural and dynamic properties of phosphatidylethanolamine and phosphatidylcholine with perdeuterated acyl chains in the solid-ordered (s) and liquid-disordered (l) phases. Our analysis of spectral lineshapes of 1,2-diperdeuteriopalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE-d) and 1,2-diperdeuteriopalmitoyl-sn-glycero-3-phosphocholine (DPPC-d) in the s (gel) phase indicated an all-trans rotating chain structure for both lipids. Greater segmental order parameters (S) were observed in the l (liquid-crystalline) phase for DPPE-d than for DPPC-d membranes, while their mixtures had intermediate values irrespective of the deuterated lipid type. Our results suggest the S profiles of the acyl chains are governed by methylation of the headgroups and are averaged over the entire system. Variations in the acyl chain molecular dynamics were further investigated by spin-lattice (R) and quadrupolar-order relaxation (R) measurements. The two acyl-perdeuterated lipids showed distinct differences in relaxation behavior as a function of the order parameter. The R rates had a square-law dependence on S, implying collective mesoscopic dynamics, with a higher bending rigidity for DPPE-d than for DPPC-d lipids. Remodeling of lipid average and dynamic properties by methylation of the headgroups thus provides a mechanism to control the actions of peptides and proteins in biomembranes.