Protrusive force

In summary, our findings suggest that cholesterol and certain analogs are a highly valuable neutral lipid component ( helper lipid ) for CL-DNA complexes because they facilitate endosomal escape by reducing the repulsive hydration and protrusion forces. They are thus able to lower the kinetic barrier for fusion of the cationic membranes of CL-DNA complexes with the anionic membrane of the endosome and increase TE, in addition to their beneficial effect on aM. 

Other mechanisms for producing protrusive force have been proposed, and not necessarily ruled out. Osmotic forces generated either by polymerization of actin or by activation of a sodium/proton antiport may be involved. It has been proposed that extensive cross-linking of actin filaments at the leading edge could produce osmotic forces that push the membrane forward [67, 68]. This hypothesis is consistent with the... 

Lipowsky R, Grotehans S (1993) Hydration versus protrusion forces between lipid bilayers. Europhys Lett 23 599-604... 

Equation 4.249 was found to fit well experimental data for the disjoining pressure of liquid films stabilized by adsorbed protein molecules bovine serum albumin (BSA) [629]. In that case, E was identified with the surface density of the loose secondary protein adsorption layer, while X turned out to be about the size of the BSA molecule. A more detailed statistical approach to the theoretical modeling of protrusion force was proposed [630]. 

The bound part of a closed vesicle is typically several nanometers away from the substrate and still shows thermal fluctuations [45], These conditions require refinement of the model by paying due attention to the mesoscopic interactions between membrane and substrate. Various forces are involved in this interaction, such as van der Waals interaction, electrostatic contributions in the case of charged membranes, and short-range repulsive forces such as the hydration force or protrusion forces [52]. 

The fusion pressure is applied against the forces that normally keep the lipid bilayers apart. These forces are well known and have been measured by various methods [7,8]. Two adjacent bilayers are attracted to each other by the van der Waals force, but are repelled by the electrostatic force at a longer range, and the hydration-protrusion force at a shorter distance. Modification of the bilayer surfaces by incorporating molecules that constitute steric bafflers has been shown to increase the interbilayer repulsion force [9,10]. Such an increase is manifested as an increase of the fusion pressure threshold, when all other parameters are held constant. 

Model systems to study the origin of protrusive force... 

R. Lipowsky and S. Grotehans. Hydration vs protrusion forces between lipid bilayers. Biophys. Chem., 49 (1994) 27—37. 

Figure 10.13 Schematic of two opposing bilayers in aqueous medium illustrating undulation and protrusion forces. Undulation forces occur between any pair of flexible...

Recent simulations indicate that the resulting repulsive interaction is, however, negligible compared to hydration forces [1263]. The reason is that the protrusion of one lipid molecule is accompanied by a correlated rearrangement of the opposing and neighboring molecules. The eSect of protrusion force is only a slight increase of the effective exponential decay length of the hydration force [1299]. 

A range of smface force methods have been used during the last 25 years for accmate measurements of classical DLVO forces (electrostatic doublelayer and van der Waals forces), polymer-induced forces (steric, bridging, depletion) under a range of solvency conditions, as well as short-range hy-dration/protrusion forces and long-range attractive forces between nonpolar surfaces in polar solvents. In particular, the interferometric stuface force... 

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