We study the growth of order following a zero temperature quench in the one-dimensional XY (n= 2)... more We study the growth of order following a zero temperature quench in the one-dimensional XY (n= 2) and Heisenberg (n= 3) models and in the two-dimensional n= 4 model with a conserved order parameter using a Langevin formalism. These systems are characterized ...
A question of considerable interest to cell membrane biology is whether phase segregated domains ... more A question of considerable interest to cell membrane biology is whether phase segregated domains across an asymmetric bilayer are strongly correlated with each other and whether phase segregation in one leaflet can induce segregation in the other. We answer both these questions in the affirmative, using an atomistic molecular dynamics simulation to study the equilibrium statistical properties of a 3-component asymmetric lipid bilayer comprising an unsaturated palmitoyl-oleoyl-phosphatidyl-choline, a saturated sphingomyelin, and cholesterol with different composition ratios. Our simulations are done by fixing the composition of the upper leaflet to be at the coexistence of the liquid ordered (l(o))-liquid disordered (l(d)) phases, while the composition of the lower leaflet is varied from the phase coexistence regime to the mixed l(d) phase, across a first-order phase boundary. In the regime of phase coexistence in each leaflet, we find strong transbilayer correlations of the l(o) dom...
Abstract: We study a minimal lattice model which describes bidirectional transport of" parti... more Abstract: We study a minimal lattice model which describes bidirectional transport of" particles" driven along a one dimensional track, as is observed in microtubule based, motor protein driven bidirectional transport of cargo vesicles, lipid bodies and organelles such ...
Proceedings of the National Academy of Sciences, 2011
Efficient and reproducible construction of signaling and sorting complexes, both on the surface a... more Efficient and reproducible construction of signaling and sorting complexes, both on the surface and within the living cell, is contingent on local regulation of biochemical reactions by the cellular milieu. We propose that in many cases this spatiotemporal regulation can be mediated by interaction with components of the dynamic cytoskeleton. We show how the interplay between active contractility and remodeling of the cytoskeleton can result in transient focusing of passive molecules to form clusters, leading to a dramatic increase in the reaction efficiency and output levels. The dynamic cytoskeletal elements that drive focusing behave as quasienzymes catalyzing the chemical reaction. These ideas are directly applicable to the cortical actin-dependent clustering of cell surface proteins such as lipid-tethered GPI-anchored proteins, Ras proteins, as well as many proteins that have domains that confer the ability to interact with the actin cytoskeleton. In general such cytoskeletal dr...
We study the shape and texture of finite domains comprising chiral or achiral molecules carrying ... more We study the shape and texture of finite domains comprising chiral or achiral molecules carrying tilt, embedded in a two-dimensional surface or membrane, using a combination of simulations and exact variational calculations. We find a variety of shapes and textures including rectangular-shaped domains and a spontaneously broken chiral texture, when the molecules are achiral. We show that chiral tilt domains nucleating in a region of two-phase coexistence repel each other, thereby preventing coalescence and further growth. Our work principally addresses observations of domains in multicomponent giant unilamellar vesicles. It may also be relevant in the study of domains in phospholipid monolayers, nucleating domains of Sm-C* in Sm-A films, and chiral emulsions in Sm-A films, in situations where we can ignore dipolar interactions.
We study the growth of order following a zero temperature quench in the one-dimensional XY (n= 2)... more We study the growth of order following a zero temperature quench in the one-dimensional XY (n= 2) and Heisenberg (n= 3) models and in the two-dimensional n= 4 model with a conserved order parameter using a Langevin formalism. These systems are characterized ...
A question of considerable interest to cell membrane biology is whether phase segregated domains ... more A question of considerable interest to cell membrane biology is whether phase segregated domains across an asymmetric bilayer are strongly correlated with each other and whether phase segregation in one leaflet can induce segregation in the other. We answer both these questions in the affirmative, using an atomistic molecular dynamics simulation to study the equilibrium statistical properties of a 3-component asymmetric lipid bilayer comprising an unsaturated palmitoyl-oleoyl-phosphatidyl-choline, a saturated sphingomyelin, and cholesterol with different composition ratios. Our simulations are done by fixing the composition of the upper leaflet to be at the coexistence of the liquid ordered (l(o))-liquid disordered (l(d)) phases, while the composition of the lower leaflet is varied from the phase coexistence regime to the mixed l(d) phase, across a first-order phase boundary. In the regime of phase coexistence in each leaflet, we find strong transbilayer correlations of the l(o) dom...
Abstract: We study a minimal lattice model which describes bidirectional transport of" parti... more Abstract: We study a minimal lattice model which describes bidirectional transport of" particles" driven along a one dimensional track, as is observed in microtubule based, motor protein driven bidirectional transport of cargo vesicles, lipid bodies and organelles such ...
Proceedings of the National Academy of Sciences, 2011
Efficient and reproducible construction of signaling and sorting complexes, both on the surface a... more Efficient and reproducible construction of signaling and sorting complexes, both on the surface and within the living cell, is contingent on local regulation of biochemical reactions by the cellular milieu. We propose that in many cases this spatiotemporal regulation can be mediated by interaction with components of the dynamic cytoskeleton. We show how the interplay between active contractility and remodeling of the cytoskeleton can result in transient focusing of passive molecules to form clusters, leading to a dramatic increase in the reaction efficiency and output levels. The dynamic cytoskeletal elements that drive focusing behave as quasienzymes catalyzing the chemical reaction. These ideas are directly applicable to the cortical actin-dependent clustering of cell surface proteins such as lipid-tethered GPI-anchored proteins, Ras proteins, as well as many proteins that have domains that confer the ability to interact with the actin cytoskeleton. In general such cytoskeletal dr...
We study the shape and texture of finite domains comprising chiral or achiral molecules carrying ... more We study the shape and texture of finite domains comprising chiral or achiral molecules carrying tilt, embedded in a two-dimensional surface or membrane, using a combination of simulations and exact variational calculations. We find a variety of shapes and textures including rectangular-shaped domains and a spontaneously broken chiral texture, when the molecules are achiral. We show that chiral tilt domains nucleating in a region of two-phase coexistence repel each other, thereby preventing coalescence and further growth. Our work principally addresses observations of domains in multicomponent giant unilamellar vesicles. It may also be relevant in the study of domains in phospholipid monolayers, nucleating domains of Sm-C* in Sm-A films, and chiral emulsions in Sm-A films, in situations where we can ignore dipolar interactions.
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