Bilayer Membrane Bending Stiffness by Tether Formation From Mixed PC-PS Lipid Vesicles

Abstract

Recently, a new approach to measure the bending stiffness (curvature elastic modulus) of lipid bilayer membrane was developed (Biophys. J., Vol. 55; pp. 509-517, 1989). The method involves the formation of cylindrical membrane strands (tethers) from bilayer vesicles. The bending stiffness (B) can be calculated from measurements of the tether radius (Rt) as a function of the axial force (f) on the tether: B = f.Rt/2 pi. In the present report, we apply this method to determine the bending stiffness of bilayer membranes composed of mixtures of SOPC (1-stearoyl-2-oleoyl phosphatidyl choline) and POPS (1-palmitoyl-2-oleoyl phosphatidyl serine). Three different mixtures were tested: pure SOPC, SOPC plus 2 percent (mol/mol) POPS, and SOPC plus 16 percent POPS. The bending stiffness determined for these three different lipid mixtures were not significantly different (1.6-1.8 x 10(-12) ergs). Because POPS carries a net negative charge, these results indicate that changes in the density of the membrane surface charge have no effect on the intrinsic rigidity of the membrane. The values we obtain are consistent with published values for the bending stiffness of other membranes determined by different methods. Measurements of the aspiration pressure, tether radius and the tether force were used to verify a theoretical relationship among these quantities at equilibrium. The ratio of the theoretical force to the measured force was 1.12 +/- 0.17.

Role of lamellar membrane structure in tether formation from bilayer vesicles

“…Similar structures were first observed as the result of mechanical deformations of red blood cell membrane (Hochmuth et al, 1973). The mechanically-formed cylinders are called tethers, and have been formed and studied in both red blood cell membrane and phospholipid vesicles of different compositions (Hochmuth et al, 1982;Bo and Waugh, 1989;Waugh, 1982a, b;Song and Waugh, 1990). Although the elastic character exhibited by tethers was originally attributed to the membrane skeleton of the red blood cell (Evans and Hochmuth, 1976), it has been recognized subsequently that tether formation is charac-teristic of the membrane bilayer, and that the stability and elastic behavior of these structures is due to the elastic resistance of bilayer membranes to changes in their curvature (Waugh and Hochmuth, 1987).…”

Formation and Maintenance of Tubular Membrane Projections Require Mechanical Force, but their Elongation and Shortening do not Require Additional Force

“…6-8 Therefore, we call these thinner tubular membrane projections membrane tethers, as described previously. [17][18][19][20][21] When the distance between the two beads reached about 12 mm, the movement of the laser was paused for 20 seconds, and then was reversed at the same speed (0.15 mm/s) (Figure 1(b)). According to the backward movement of the bead, the tethers gradually shortened.…”

“…Since the protrusion is a characteristic shape of lipid membranes, the mechanism underlying protrusion is a key to understand lipid membrane morphogenesis. In previous studies, lipid membrane vesicles or cell membranes were pulled by using an aspiration pipette or by manipulating beads connected to the outside surface of the membrane, [15][16][17][18][19][20][21][22][23] and the force strength required to transform the membranes was measured. As a result, narrow tubular membrane projections (membrane tethers) were formed, and the tension and bending stiffness of lipid bilayers were obtained by mechanical analyses of those tethers.…”

Influenza A matrix protein M1 is sufficient to induce lipid membrane deformation

“…Additionally, our observation that significant shape alteration is observed only in bilayers containing higher amounts of PS is likely not connected to an effect of this lipid on the physical properties of the membrane. It was shown in fact that PS does not decrease the bending stiffness of a lipid bilayer (43,44). In conclusion, the observed alterations in bilayer shape are brought about specifically by the binding of M1 to the membrane.…”