Polar Interactions Play an Important Role in the Energetics of the Main Phase Transition of Phosphatidylcholine Membranes

Abstract

Conformational changes of membrane proteins are accompanied by deformation in the surrounding lipid bilayer. To gain insight into the energetics of membrane deformation, the phase behavior of dimyristoylphosphatidylcholine (DMPC) membranes in the presence of the dipole potential, ψ d , modifiers was investigated by differential scanning calorimetry. 7-Ketocholesterol, which weakens ψ d and reduces membrane-perpendicular dipole–dipole repulsion, causes a discrete second peak on the high-temperature side of the main transition, whereas 6-ketocholestanol, which strengthens ψ d and increases membrane-perpendicular dipole–dipole repulsion, merely produces a shoulder. Measurements on pure DMPC vesicles showed that the observed temperature profile could not be explained by a single endothermic process, that is, breaking of van der Waals forces between hydrocarbon chains alone. Removal of NaCl from the buffer caused an increase in the main transition temperature and the appearance of an obvious shoulder, implicating polar interactions. Consideration of the phosphatidylcholine (PC) head group dipole moment indicates direct interactions between PC dipoles that are unlikely to account for the additional process. It seems more likely that the breaking of an in-plane hydrogen-bonded network consisting of hydrating water dipoles together with zwitterionic lipid head groups is responsible. The evidence presented supports the idea that the breaking of van der Waals forces between lipid tails required for the main phase transition of PC membranes is coupled to partial breaking of a hydrogen-bonded network at the membrane surface.

Antimicrobial Mechanism of “Fatty Acyl Glutamic Acid” Biosurfactant against Escherichia coli O157:H7 and Listeria monocytogenes Involves Disruption of the Cytoplasmic Membrane

“…21,55,56 Considering the nonideal mixing of FA-glu with PLs, the fluidity of the LBL comprising FA-glu and PLs then relied on the polar interactions of their head-groups that are accounted in terms of the changes in enthalpy (ΔH) and the nonpolar interactions for the hydrophobic chains accounted as changes in the entropy. 57 The T m that largely defines the entropy state for an LBL account for the relative motilities of the FA-glu and PLs combined, which is then governed by both the polar 58 and nonpolar interactions. Thus, the changes in H and T m for the PLs representing E. coli O157:H7 and L. monocytogenes, upon dissolution of FA-glu, provided an estimate of the alterations in the physical statethe LBL fluidityof the cell membranes of these bacterium types.…”

Evidence for ATP Interaction with Phosphatidylcholine Bilayers

“…These transitions can be altered by compounds that disrupt the phospholipid bilayer packing structure. The classic example is cholesterol. , If ATP were interacting with the phospholipid bilayer and altering the strength of the interactions between individual phospholipids, a change in the main phase transition temperature and enthalpy would be expected.…”

Competing for the same space: protons and alkali ions at the interface of phospholipid bilayers

“…The free energy, ΔG, was obtained from ΔG(z) = − RT ln p(z), where p(z) is the normalised number density of a given system component at position z along the bilayer normal, calculated from MD simulations of a proton near the surface of a hydrated DMPC lipid bilayer. Reprinted from Wolf et al (2014) with permission from Elsevier monovalent ions (Garcia-Manyes et al 2005;Garcia-Manyes et al 2006;Garcia et al 2019;Piantanida et al 2017). In addition, simulations have demonstrated changes to the area per lipid, order parameters, diffusion coefficients and orientations of the headgroup dipole (Böckmann et al 2003;Cordomí et al 2008;Gurtovenko and Vattulainen 2008;Reif et al 2017;Vácha et al 2009).…”

“…Both protons and alkali ions are small cations that have been shown to bind to the water-lipid interface of phospholipid membranes and, through these water-ion-lipid interactions, have the capacity to change the structure and physicochemical properties of membranes (Böckmann et al 2003;Cordomí et al 2009;Cranfield et al 2016;Deplazes et al 2017;Garcia-Manyes et al 2005;Garcia-Manyes et al 2006;Garcia et al 2019;Koynova and Caffrey 1998;Petelska and Figaszewski 2002;Piantanida et al 2017;Reif et al 2017;Vácha et al 2009). As we will outline in this review, in many cases, the reported findings on how protons and alkali ions interact with phospholipid membranes This article is part of a Special Issue dedicated to the '2018 Joint Conference of the Asian Biophysics Association and Australian Society for Biophysics' edited by Kuniaki Nagayama, Raymond Norton, Kyeong Kyu Kim, Hiroyuki Noji, Till Böcking, and Andrew Battle.…”