343 research outputs found
How does torsional rigidity affect the wrapping transition of a semiflexible chain around a spherical core?
We investigated the effect of torsional rigidity of a semiflexible chain on
the wrapping transition around a spherical core, as a model of nucleosome, the
fundamental unit of chromatin. Through molecular dynamics simulation, we show
that the torsional effect has a crucial effect on the chain wrapping around the
core under the topological constraints. In particular, the torsional stress (i)
induces the wrapping/unwrapping transition, and (ii) leads to a unique complex
structure with an antagonistic wrapping direction which never appears without
the topological constraints. We further examine the effect of the stretching
stress for the nucleosome model, in relation to the unique characteristic
effect of the torsional stress on the manner of wrapping
Coupling between pore formation and phase separation in charged lipid membranes
We investigated the effect of charge on the membrane morphology of giant
unilamellar vesicles (GUVs) composed of various mixtures containing charged
lipids. We observed the membrane morphologies by fluorescent and confocal laser
microscopy in lipid mixtures consisting of a neutral unsaturated lipid
[dioleoylphosphatidylcholine (DOPC)], a neutral saturated lipid
[dipalmitoylphosphatidylcholine (DPPC)], a charged unsaturated lipid
[dioleoylphosphatidylglycerol (DOPG)], a charged saturated
lipid [dipalmitoylphosphatidylglycerol (DPPG)], and
cholesterol (Chol). In binary mixtures of neutral DOPC/DPPC and charged
DOPC/DPPG, spherical vesicles were formed. On the other
hand, pore formation was often observed with GUVs consisting of
DOPG and DPPC. In a DPPC/DPPG/Chol
ternary mixture, pore-formed vesicles were also frequently observed. The
percentage of pore-formed vesicles increased with the DPPG
concentration. Moreover, when the head group charges of charged lipids were
screened by the addition of salt, pore-formed vesicles were suppressed in both
the binary and ternary charged lipid mixtures. We discuss the mechanisms of
pore formation in charged lipid mixtures and the relationship between phase
separation and the membrane morphology. Finally, we reproduce the results seen
in experimental systems by using coarse-grained molecular dynamics simulations.Comment: 34 pages, 10 figure
Lateral transport of domains in anionic lipid bilayer membranes under DC electric fields: A coarse-grained molecular dynamics study
Dynamic lateral transport of lipids, proteins, and self-assembled structures
in biomembranes plays crucial roles in diverse cellular processes. In this
study, we perform a coarse-grained molecular dynamics simulation on a vesicle
composed of a binary mixture of neutral and anionic lipids to investigate the
lateral transport of individual lipid molecules and the self-assembled lipid
domains upon an applied direct current (DC) electric field. Under the potential
force of the electric field, a phase-separated domain rich in the anionic
lipids is trapped in the opposite direction of the electric field. The
subsequent reversal of the electric field induces the unidirectional domain
motion. During the domain motion, the domain size remains constant, but a
considerable amount of the anionic lipids is exchanged between the
anionic-lipid-rich domain and the surrounding bulk. While the speed of the
domain motion (collective lipid motion) shows a significant positive
correlation with the electric field strength, the exchange of anionic lipids
between the domain and bulk (individual lipid motion) exhibits no clear
correlation with the field strength. The mean velocity field of the lipids
surrounding the domain displays a two-dimensional (2D) source dipole. We
revealed that the balance between the potential force of the applied electric
field and the quasi-2D hydrodynamic frictional force well explains the
dependence of the domain motions on the electric-field strengths. The present
results provide insight into the hierarchical dynamic responses of
self-assembled lipid domains to the applied electric field and contribute to
controlling the lateral transportation of lipids and membrane inclusions.Comment: 9 pages, 6 figure
Photodecomposition Behaviors of Pesticides in the Source for Water Supply Using an Alumina Carrier-Titanium Dioxide Photocatalyst
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