The Role of Lateral Tension in Calcium-Induced DPPS Vesicle Rupture

Abstract

We assess the role of lateral tension in rupturing anionic dipalmitoylphosphatidyserine (DPPS), neutral dipalmitoylphosphatidylcholine (DPPC), and mixed DPPS-DPPC vesicles. Binding of Ca2+ is known to have a significant impact on the effective size of DPPS lipids and little effect on the size of DPPC lipids in bilayer structures. In the present work we utilized laser transmission spectroscopy (LTS) to assess the effect of Ca2+ induced stress on the stability of the DPPS and DPPC vesicles. The high sensitivity and resolution of LTS has permitted the determination of the size and shape of liposomes in solution. The results indicate a critical size after which DPPS single shell vesicles are no longer stable. Our measurements indicate Ca2+ promotes bilayer fusion up to a maximum diameter of ca. 320 nm. These observations are consistent with a straightforward free-energy-based model of vesicle rupture involving lateral tension between lipids regulated by the binding of Ca2+. Our results support a critical role of lateral interactions within lipid bilayers for controlling such processes as the formation of supported bilayer membranes and pore formation in vesicle fusion. Using this free energy model we are able to infer a lower bound for the area dilation modulus for DPPS (252 pN/nm) and demonstrate a substantial free energy increase associated with vesicle rupture.

Surface Enhanced Raman Correlation Spectroscopy of Particles in Solution

“…28 For SERS experiments, vesicle solutions were diluted to 0.05 wt % with nanopure water (18.2 MΩ-cm, Thermo Scientific). Polystyrene beads (Sigma-Aldrich) of varying sizes (1100, 300, and 100 nm) were diluted to 0.001 wt % in nanopure water.…”

“…Solutions containing 1,2-dipalmityol- sn -glycero-3-phosphocholine (DPPC) (Avanti Polar Lipids) single-shell vesicles of varying sizes were prepared by extrusion through polycarbonate filters (Whatman, Nuclepore) with decreasing pore size (1000, 400, 200, and 100 nm). 28 For SERS experiments, vesicle solutions were diluted to 0.05 wt % with nanopure water (18.2 MΩ-cm, Thermo Scientific). Polystyrene beads (Sigma-Aldrich) of varying sizes (1100, 300, and 100 nm) were diluted to 0.001 wt % in nanopure water.…”

Versatile self-assembly of supramolecular block copolymers with ionic cluster junctions

“…When decreasing the concentration of CBC-2 from 0.5 to 0.2 mg mL −1 , the R h of CBC-2 vesicles decreases from 150 to 70 nm (Fig. 19 Our results just represent an opposite case. On the other hand, the increase of temperature from 25 to 45°C also causes the R h of CBC-2 vesicles to gradually decrease from 150 to 80 nm ( Fig.…”

Fluctuation-Driven Transport in Biological Nanopores. A 3D Poisson–Nernst–Planck Study

“…The existence of a charged membrane was simulated adding a small charged region, 5 Å wide, at one of the channel sides, over the ion inaccessible membrane region. The charge was adjusted to mimic a surface charge of about 1 negative elementary charge every 44.2 Å 2 (approximately the area per lipid for dipalmitoyl phosphatidylcholine (DPPS) lipid [21]). …”