1,774 research outputs found
The mean-field theory for attraction between like-charged macromolecules
A mean-field theory based on Gibbs-Bogoliubov inequality is constructed to
study the interactions between two like-charged polyions. It is shown that
contrary to the previously established paradigm, a properly constructed
mean-field theory can quantitatively account for the attractive interactions
between two like-charged rods.Comment: 5 pages, 2 figures, elsart.sty neede
Wigner crystal model of counterion induced bundle formation of rod-like polyelectrolytes
A simple electrostatic theory of condensation of rod-like polyelectrolytes
under influence of polyvalent ions is proposed. It is based on the idea that
Manning condensation of ions results in formation of the Wigner crystal on a
background of a bundle of rods. It is shown that, depending on a single
dimensionless parameter, this can be the densely packed three-dimensional
Wigner crystal or the two-dimensional crystal on the rod surfaces. For DNA the
location of charge on the spiral results in a model of the one-dimensional
Wigner crystal. It is also argued that the Wigner crystal idea can be applied
to self-assembly of other polyelectrolytes, for example, colloids and DNA-lipid
complexes.Comment: 4 pages; typos corrected, references adde
Intracellular consequences of SOS1 deficiency during salt stress
A mutation of AtSOS1 (Salt Overly Sensitive 1), a plasma membrane Na+/H+-antiporter in Arabidopsis thaliana, leads to a salt-sensitive phenotype accompanied by the death of root cells under salt stress. Intracellular events and changes in gene expression were compared during a non-lethal salt stress between the wild type and a representative SOS1 mutant, atsos1-1, by confocal microscopy using ion-specific fluorophores and by quantitative RT-PCR. In addition to the higher accumulation of sodium ions, atsos1-1 showed inhibition of endocytosis, abnormalities in vacuolar shape and function, and changes in intracellular pH compared to the wild type in root tip cells under stress. Quantitative RT-PCR revealed a dramatically faster and higher induction of root-specific Ca2+ transporters, including several CAXs and CNGCs, and the drastic down-regulation of genes involved in pH-homeostasis and membrane potential maintenance. Differential regulation of genes for functions in intracellular protein trafficking in atsos1-1 was also observed. The results suggested roles of the SOS1 protein, in addition to its function as a Na+/H+ antiporter, whose disruption affected membrane traffic and vacuolar functions possibly by controlling pH homeostasis in root cells
Conformational Instability of Rodlike Polyelectrolytes due to Counterion Fluctuations
The effective elasticity of highly charged stiff polyelectrolytes is studied
in the presence of counterions, with and without added salt. The rigid polymer
conformations may become unstable due to an effective attraction induced by
counterion density fluctuations. Instabilities at the longest, or intermediate
length scales may signal collapse to globule, or necklace states, respectively.
In the presence of added-salt, a generalized electrostatic persistence length
is obtained, which has a nontrivial dependence on the Debye screening length.
It is also found that the onset of conformational instability is a re-entrant
phenomenon as a function of polyelectrolyte length for the unscreened case, and
the Debye length or salt concentration for the screened case. This may be
relevant in understanding the experimentally observed re-entrant condensation
of DNA.Comment: 8 pages, 4 figure
Charge Fluctuations on Membrane Surfaces in Water
We generalize the predictions for attractions between over-all neutral
surfaces induced by charge fluctuations/correlations to non-uniform systems
that include dielectric discontinuities, as is the case for mixed charged lipid
membranes in an aqueous solution. We show that the induced interactions depend
in a non-trivial way on the dielectric constants of membrane and water and show
different scaling with distance depending on these properties. The generality
of the calculations also allows us to predict under which dielectric conditions
the interaction will change sign and become repulsive
Chiral Structure of F-actin Bundle Formed by Multivalent Counterions?
The mechanism of multivalent counterion-induced bundle formation by
filamentous actin (F-actin) is studied using a coarse-grained model and
molecular dynamics simulation. Real diameter size, helically ordered charge
distribution and twist rigidity of F-actin are taken into account in our model.
The attraction between parallel F-actins induced by multivalent counterions is
studied in detail and it is found that the maximum attraction occurs between
their closest charged domains. The model F-actins aggregate due to the
like-charge attraction and form closely packed bundles. Counterions are mostly
distributed in the narrowest gaps between neighboring F-actins inside the
bundles and the channels between three adjacent F-actins correspond to low
density of the counterions. Density of the counterions varies periodically with
a wave length comparable to the separation between consecutive G-actin monomers
along the actin polymers. Long-lived defects in the hexagonal order of F-actins
in the bundles are observed that their number increases with increasing the
bundles size. Combination of electrostatic interactions and twist rigidity has
been found not to change the symmetry of F-actin helical conformation from the
native 13/6 symmetry. Calculation of zero-temperature energy of hexagonally
ordered model F-actins with the charge of the counterions distributed as
columns of charge domains representing counterion charge density waves has
shown that helical symmetries commensurate with the hexagonal lattice
correspond to local minima of the energy of the system. The global minimum of
energy corresponds to 24/11 symmetry with the columns of charge domains
arranged in the narrowest gaps between the neighboring F-actins.Comment: 9 pages, 10 figures, Published online in Soft Matter journal:
http://pubs.rsc.org/en/content/articlelanding/2012/sm/c2sm07104
Investigating the distance limit of a metal nanoparticle based spectroscopic ruler
Conventional FĂśrster resonance energy transfer (FRET) processes involving a pair of fluorophore and organic quencher are restricted to an upper distance limit of ~10 nm. The application of a metal nanoparticle as a quencher can overcome the distance barrier of the traditional FRET technique. However, no standard distance dependence of this resonance energy transfer (RET) process has been firmly established. We have investigated the nonradiative energy transfer process between an organic donor (fluorescein) and gold nanoparticle quencher connected by double stranded (ds) DNA. The quenching efficiency of the gold nanoparticle as a function of distance between the donor and acceptor was determined by time-resolved lifetime analyses of the donor. Our results showed a 1/d4 distance dependence for the RET process for longer distances (>10 nm) and 1/d6 distance dependence for shorter distances (<10 nm). Our results clearly indicate the applicability of metal nanoparticle based quenchers for studying systems that exceed the 10 nm FRET barrier
Biotechnology for mechanisms that counteract salt stress in extremophile species: A genome-based view
Molecular genetics has confirmed older research and generated new insights into the ways how plants deal with adverse conditions. This body of research is now being used to interpret stress behavior of plants in new ways, and to add results from most recent genomics-based studies. The new knowledge now includes genome sequences of species that show extreme abiotic stress tolerances, which enables new strategies for applications through either molecular breeding or transgenic engineering. We will highlight some physiological features of the extremophile lifestyle, outline emerging features about halophytism based on genomics, and discuss conclusions about underlying mechanisms. Š 2012 Korean Society for Plant Biotechnology and Springer
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