Simulation Studies of Structure and Edge Tension of Lipid Bilayer Edges: Effects of Tail Structure and Force-Field

Abstract

Molecular dynamics simulations of lipid bilayer ribbons have been performed to investigate the structures and line tensions associated with free bilayer edges. Simulations carried out for dioleoyl phosphatidylcholine with three different force-field parameter sets yielded edge line tensions of 45 ± 2 pN, over 50% greater than the most recently reported experimentally determined value for this lipid. Edge tensions obtained from simulations of a series of phosphatidylcholine lipid bilayer ribbons with saturated acyl tails of length 12-16 carbons and with monounsaturated acyl tails of length 14-18 carbons could be correlated with the excess area associated with forming the edge, through a two-parameter fit. Saturated-tail lipids underwent local thickening near the edge, producing denser packing that correlated with lower line tensions, while unsaturated-tail lipids showed little or no local thickening. In a dipalmitoyl phosphatidylcholine ribbon initiated in a tilted gel-phase structure, lipid headgroups tended to tilt toward the nearer edge producing a herringbone pattern, an accommodation that may account for the reported edge-induced stabilization of an ordered structure at temperatures near a lipid gel-fluid phase transition.

Line tension of the pore edge in phospholipid/cholesterol bilayer from stretch molecular dynamics simulation

“…The upper and lower limits of the line tensions of the bilayers containing cholesterol at 0, 20, and 40 mol% are estimated to be 17.0-48.2, 54.5-100, and 170-261 pN, respectively. The line tension of the pure DPPC bilayer is in agreement with those estimated by different methods in previous MD simulation studies (27.5-50 pN) (Leontiadou et al, 2004;West et al, 2013;Wohlert et al, 2006). The line tension increases with the increase of the cholesterol concentration, which qualitatively agrees with those for similar phospholipid bilayers reported from experiments (Karatekin et al, 2003;Zhelev and Needham, 1993).…”

“…Bilayers with a pore are prepared through equibiaxial stretching simulations of intact bilayers. Stretch-induced pore formation was proposed to be more suitable for our purpose, the investigation of pore dynamics under mechanical stresses, than several other protocols used for making a pore employed in previous studies, such as self-aggregation (Leontiadou et al, 2004) and manual construction (Tolpekina et al, 2004;West et al, 2013). However, it is noted that the pore structures are very similar despite the different protocols used for the pore formation (Marrink et al, 2009).…”

“…Thus, the line tension L, which governs RC, is an important property of the bilayer and is useful for discussing the bilayer-edge-related phenomena, that is, rupture. The estimations of the line tension have been conducted by experimental (Karatekin et al, 2003;Portet and Dimova, 2010;Zhelev and Needham, 1993), theoretical (Akimov et al, 2014), and computational studies (Tolpekina et al, 2004;West et al, 2013;Wohlert et al, 2006). In these experiments, researchers have estimated the line tension from the pore closure dynamics in giant bilayer vesicles under stresses.…”

“…These studies reported that the line tension depends on not only the lipid composition of the bilayer but also the purity of the lipids (Karatekin et al, 2003). In computational studies, molecular dynamics (MD) simulations of planar bilayer systems with a pore (Tolpekina et al, 2004) or bilayer ribbon system (West et al, 2013) have been performed. These studies clarified that the molecular details of the bilayer edge structure, and the line tensions estimated in MD simulations (10-50 pN) are in qualitative agreement with those obtained from experiments (5-30 pN).…”

Lipid tail protrusions mediate the insertion of nanoparticles into model cell membranes

“…The DOPC bilayer was assembled as a ribbon following the protocol described recently by West et al 69 The ribbon was constructed by first equilibrating a 200 lipid bilayer at constant volume and pressure for 100 ns, then duplicating the bilayer in the x direction while adding additional water to put 10 nm of space between the edges of the 400 lipid bilayer across the periodic boundaries before re-equilibrating.…”