Membrane deformability

COPI vesicle budding is triggered by the hydrolysis of GTP to GDP by membrane-associated ARFl. Once in the membranes, ARF-GTP recruits pre-assembled coatomers, resulting in membrane deformation. The cytoplasmic tail of an abundant transmembrane protein, known as p24,... 

Fig. 5.59 shows a section through a Piezo-resistive silicon pressure sensor. The ambient pressure is applied from above, while the pressure being measured is applied from below. A silicon membrane that deforms under the pressure is applied to a silicon carrier structure. Piezo-resistive structures are fitted in the membrane, which then change their resistance accordingly when the membrane deforms. A bridge circuit generates an electrical output signal which is proportional to the difference in pressure. 

The total volume of solution within the capsule is V = Vwn w + V+ni+ + V-tii- + Vvv I,. When the pressure within the capsule varies, the surrounding membrane deforms by an amount that depends upon its mechanical properties. If the change in capsule volume is small, we may assume a linear relation... 

The parameter which is measured in this test is the pressure of underwater explosion. Lead or copper membranes are employed, and the membrane deformation as a function of the performance of the explosive and of the distance from the explosion site is estimated. The measuring apparatus, consisting of piston and anvil, resembles the Kast brisance meter. An alternative technique is to measure the deformation of diaphragms or copper discs accommodated inside an air-containing vessel such as a can. 

The aim is to eliminate entrance effects as much as possible and any influence on the flow of the pressure tap holes into the channels. This was achieved by integrating on the same silicon chip the microchannel, the pressure taps and the pressure sensors. The fabrication process and the operating mode are described in [28]. The pressure sensors are constituted cf a membrane which is deformed under the fluid pressure and on which is deposited a thin film strain gauge. This strain gauge forms a Wheatstone bridge whose the membrane deformation modifies the electrical resistances. 

Our method uses an atomic-level representation of the adsorbing protein in three dimensions, and accounts for lateral reorganization and demixing of lipids, as well as membrane deformations upon adsorption (see Figure 1). We consider the limit of low surface density of adsorbing proteins, so that interactions between... 

In fact, F is also required to be at a minimum with respect to all possible membrane deformations, and this minimization with respect to membrane shape must be carried out self-consistently together with the electrostatic and lipid mixing contributions [27,36]. This presents a challenge, since in principle one has to consider all possible variations in membrane geometry, and these multiple shape deformations generally couple to other degrees of freedom. 

Here, F0id and Fnew are, respectively, the adsorption free energies of the "old" state (before the trial move) and "new" state of the protein-membrane system. If a trial move is accepted, the macromolecule is advanced to the "new" position, the CH equations for lipids are solved, and sampling of membrane deformations are performed for the newly accepted position of the adsorbate. If, on the other hand, the trial move is rejected, the protein remains at its previous position, and the same minimization step is conducted, only now with respect to the previous "old" location of the adsorbate. 

From the corresponding model binding free energy (AF) we can conclude that lipid demixing and membrane deformations contribute to a lowering AF for BAR/PS/PC and BAR/PIP2/PC complexes by 1.9 kBT and 1.7 kBT, respectively,... 

N-helix insertions can potentially enhance membrane deformations... 

In order to explore whether insertions of the BAR dimer s N-helices can enhance membrane curvature, various penetration depths of N-helices were examined, and the results are illustrated in Figure 3. We observe larger membrane deformations upon deeper insertion of N-helices (represented in the model by increasing the local spontaneous curvature). By performing quantitative analysis on binding... 

Khelashvili, G., Harries, D., Weinstein, H. Modeling membrane deformations and lipid demixing upon protein-membrane interaction The BAR dimer adsorption. Biophys. J. 2009, 97,1626-35. 

Receptor-Mediated Endocytosis. Mammalian cells have developed an assortment of mechanisms to facilitate the internalization of specific substrates and target these to defined locations inside the cytoplasm. Collectively, these processes of membrane deformations are termed "endocytosis," consisting of phagocytosis, pinocytosis, receptor-mediated endocytosis (clathrin-mediated), and potocytosis [nonclathrin (caveolin)-mediated RME]. The emphasis of this section is receptor-mediated endocytosis in the intestinal tract, but the interested student may consult alternative reviews covering the complete spectrum of endo-cytotic processes in other cell types (17,18). 

Pasvol, G., Chasis, J. A., Mohandas, N., Anstee, D. J., Tanner, M. J., and Merry, A. H. (1989). Inhibition of malarial parasite invasion by monoclonal antibodies against glycophorin A correlates with reduction in red cell membrane deformability. Blood 74,1836-1843. 

Being perturbed at the interface, the membrane profile u r) adjusts itself gradually to minimize the elastic energy. The corresponding free energy of membrane deformation can strongly affect both protein conformation and protein function. For the GA insertion considered below, these effects manifest themselves through the influence of membrane parameters (elastic constants, thickness of the bilayer) on the lifetime r of the ion channel,... 

---