Translational diffusion of lipids in liquid crystalline phase phosphatidylcholine multibilayers. A comparison of experiment with theory

Abstract

A systematic study of the translational diffusion of the phospholipid derivative N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (NBD-PE) has been undertaken in liquid crystalline phase phosphatidylcholine bilayers by using the fluorescence recovery after photobleaching technique. This work was done with the intention of comparing the experimental results with the predictions of theoretical models for diffusion in membranes. The following is shown. For NBD-PE, the dependence of the translational diffusion coefficient (Dt) upon the acyl chain length of the diffusant is not that predicted by continuum fluid hydrodynamic models for diffusion in membranes [Saffman, P.G., & Delbrueck, M. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 3111-3113; Hughes, B. D., Pailthorpe, B. A., & White, L. R. (1981) J. Fluid Mech. 110, 349-372]. Plots of Dt vs. 1/T (Arrhenius plots) are nonlinear in dilauroyl-phosphatidylcholine (DLPC), dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) bilayers where the acyl chain composition of the NBD-PE is matched with that of the host bilayer lipid. This suggests that a "free volume" model may be appropriate for the description of lipid diffusion in lipid bilayers. In bilayers of phosphatidylcholines with saturated acyl chains at the same "reduced temperature", the magnitude of Dt follows the order distearoylphosphatidylcholine greater than DPPC greater than DMPC greater than DLPC. This is the inverse of what may be expected from the hydrodynamic model but is in agreement with the free volume in these bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Behaviour of NBD-head group labelled phosphatidylethanolamines in POPC bilayers: a molecular dynamics study

“…Compared to the host lipid, probe diffusion is generally slower, which can be explained on account of the interactions between the NBD group and both the solvent and the host lipid (the fluorophore of NBD-diC n PE is effectively replacing the choline group of PC, which is incapable of hydrogen bonding). Overall, there are no established trends of variation of lateral diffusion coefficients with increasing chain length, in agreement with the FRAP measurements of Vaz et al 78 The two possibly variant results are the calculated higher value of NBD-diC 10 PE and the lower value of NBD-diC 18 PE. Although both could be regarded as outliers stemming from the small number of probe molecules sampled (the shapes of the respective MSD curves seem to differ from those of the other derivatives), it is possible that an increased D value for intermediate chain length results as a compromise between two opposing effects: on the one hand, the increased order of the bilayer for longer chains, which would per se lead to a continuous decrease in D; on the other hand, the increasing weight of the acyl chain atoms (which are located in a more fluid region of the bilayer, and therefore more capable of shortrange segmental motions that are taken into account in our MSD calculation).…”

An implicit solvent coarse-grained lipid model with correct stress profile

“…III A above on internal bilayer time scales͒. The coarse-grained diffusion constant nicely matches the reported experimental values of the DPPC diffusion constant, 46 approximately 1 ϫ 10 −7 cm 2 s −1 . Lipid flip flop, the exchange in lipids between the inner and outer leaflets of the bilayer, has been characterized experimentally to have a very slow time scale ͑hours͒ in model membranes, although when catalyzed it is much faster.…”

Strong influence of periodic boundary conditions on lateral diffusion in lipid bilayer membranes

“…For example, even within the context of non-continuum "free area" theories for lipid diffusion, hydrodynamic traction from the surrounding water may still influence diffusivities. 61 In such a case, PBC would still be expected to influence lipid diffusivity, even though the predictions of Appendix B may be quantitatively off.…”