1,071 research outputs found
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
Structural Transition of Actin Filament in a Cell-Sized Water Droplet with a Phospholipid Membrane
Actin filament, F-actin, is a semiflexible polymer with a negative charge,
and is one of the main constituents on cell membranes. To clarify the effect of
cross-talk between a phospholipid membrane and actin filaments in cells, we
conducted microscopic observations on the structural changes in actin filaments
in a cell-sized (several tens of micrometers in diameter) water droplet coated
with a phospholipid membrane such as phosphatidylserine (PS; negatively-charged
head group) or phosphatidylethanolamine (PE; neutral head group) as a simple
model of a living cell membrane. With PS, actin filaments are distributed
uniformly in the water phase without adsorption onto the membrane surface
between 2 and 6 mM Mg2+, while between 6 and 12 mM Mg2+, actin filaments are
adsorbed onto the inner membrane surface. With PE, actin filaments are
uniformly adsorbed onto the inner membrane surface between 2 and 12 mM Mg2+.
With both PS and PE membranes, at Mg2+ concentrations higher than 12 mM, thick
bundles are formed in the bulk water droplet accompanied by the dissolution of
actin filaments from the membrane surface. The attraction between actin
filaments and membrane is attributable to an increase in the translational
entropy of counterions accompanied by the adsorption of actin filaments onto
the membrane surface. These results suggest that a microscopic water droplet
coated with phospholipid can serve as an easy-to-handle model of cell
membranes
Spontaneous Oscillations of Collective Molecular Motors
We analyze a simple stochastic model to describe motor molecules which
cooperate in large groups and present a physical mechanism which can lead to
oscillatory motion if the motors are elastically coupled to their environment.
Beyond a critical fuel concentration, the non-moving state of the system
becomes unstable with respect to a mode with angular frequency omega. We
present a perturbative description of the system near the instability and
demonstrate that oscillation frequencies are determined by the typical
timescales of the motors.Comment: 11 pages, Revtex, 4 pages Figure
Effects of thermal fluctuation and the receptor-receptor interaction in bacterial chemotactic signalling and adaptation
Bacterial chemotaxis is controlled by the conformational changes of the
receptors, in response to the change of the ambient chemical concentration. In
a statistical mechanical approach, the signalling due to the conformational
changes is a thermodynamic average quantity, dependent on the temperature and
the total energy of the system, including both ligand-receptor interaction and
receptor-receptor interaction. This physical theory suggests to biology a new
understanding of cooperation in ligand binding and receptor signalling
problems. How much experimental support of this approach can be obtained from
the currently available data? What are the parameter values? What is the
practical information for experiments? Here we make comparisons between the
theory and recent experimental results. Although currently comparisons can only
be semi-quantitative or qualitative, consistency is clearly shown. The theory
also helps to sort a variety of data.Comment: 26 pages, revtex. Journal version. Analysis on another set of data on
adaptation time is adde
Optineurin links myosin VI to the Golgi complex and is involved in Golgi organization and exocytosis.
Myosin VI plays a role in the maintenance of Golgi morphology and in exocytosis. In a yeast 2-hybrid screen we identified optineurin as a binding partner for myosin VI at the Golgi complex and confirmed this interaction in a range of protein interaction studies. Both proteins colocalize at the Golgi complex and in vesicles at the plasma membrane. When optineurin is depleted from cells using RNA interference, myosin VI is lost from the Golgi complex, the Golgi is fragmented and exocytosis of vesicular stomatitis virus G-protein to the plasma membrane is dramatically reduced. Two further binding partners for optineurin have been identified: huntingtin and Rab8. We show that myosin VI and Rab8 colocalize around the Golgi complex and in vesicles at the plasma membrane and overexpression of constitutively active Rab8-Q67L recruits myosin VI onto Rab8-positive structures. These results show that optineurin links myosin VI to the Golgi complex and plays a central role in Golgi ribbon formation and exocytosis
Optogenetics and deep brain stimulation neurotechnologies
Brain neural network is composed of densely packed, intricately wired neurons whose activity patterns ultimately give rise to every behavior, thought, or emotion that we experience. Over the past decade, a novel neurotechnique, optogenetics that combines light and genetic methods to control or monitor neural activity patterns, has proven to be revolutionary in understanding the functional role of specific neural circuits. We here briefly describe recent advance in optogenetics and compare optogenetics with deep brain stimulation technology that holds the promise for treating many neurological and psychiatric disorders
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