17,933 research outputs found
Comparable contributions of structural-functional constraints and expression level to the rate of protein sequence evolution
<p>Abstract</p> <p>Background</p> <p>Proteins show a broad range of evolutionary rates. Understanding the factors that are responsible for the characteristic rate of evolution of a given protein arguably is one of the major goals of evolutionary biology. A long-standing general assumption used to be that the evolution rate is, primarily, determined by the specific functional constraints that affect the given protein. These constrains were traditionally thought to depend both on the specific features of the protein's structure and its biological role. The advent of systems biology brought about new types of data, such as expression level and protein-protein interactions, and unexpectedly, a variety of correlations between protein evolution rate and these variables have been observed. The strongest connections by far were repeatedly seen between protein sequence evolution rate and the expression level of the respective gene. It has been hypothesized that this link is due to the selection for the robustness of the protein structure to mistranslation-induced misfolding that is particularly important for highly expressed proteins and is the dominant determinant of the sequence evolution rate.</p> <p>Results</p> <p>This work is an attempt to assess the relative contributions of protein domain structure and function, on the one hand, and expression level on the other hand, to the rate of sequence evolution. To this end, we performed a genome-wide analysis of the effect of the fusion of a pair of domains in multidomain proteins on the difference in the domain-specific evolutionary rates. The mistranslation-induced misfolding hypothesis would predict that, within multidomain proteins, fused domains, on average, should evolve at substantially closer rates than the same domains in different proteins because, within a mutlidomain protein, all domains are translated at the same rate. We performed a comprehensive comparison of the evolutionary rates of mammalian and plant protein domains that are either joined in multidomain proteins or contained in distinct proteins. Substantial homogenization of evolutionary rates in multidomain proteins was, indeed, observed in both animals and plants, although highly significant differences between domain-specific rates remained. The contributions of the translation rate, as determined by the effect of the fusion of a pair of domains within a multidomain protein, and intrinsic, domain-specific structural-functional constraints appear to be comparable in magnitude.</p> <p>Conclusion</p> <p>Fusion of domains in a multidomain protein results in substantial homogenization of the domain-specific evolutionary rates but significant differences between domain-specific evolution rates remain. Thus, the rate of translation and intrinsic structural-functional constraints both exert sizable and comparable effects on sequence evolution.</p> <p>Reviewers</p> <p>This article was reviewed by Sergei Maslov, Dennis Vitkup, Claus Wilke (nominated by Orly Alter), and Allan Drummond (nominated by Joel Bader). For the full reviews, please go to the Reviewers' Reports section.</p
Spin-filter tunnel junction with matched Fermi surfaces
Efficient injection of spin-polarized current into a semiconductor is a basic
prerequisite for building semiconductor-based spintronic devices. Here, we use
inelastic electron tunneling spectroscopy to show that the efficiency of
spin-filter-type spin injectors is limited by spin scattering of the tunneling
electrons. By matching the Fermi-surface shapes of the current injection source
and target electrode material, spin injection efficiency can be significantly
increased in epitaxial ferromagnetic insulator tunnel junctions. Our results
demonstrate that not only structural but also Fermi-surface matching is
important to suppress scattering processes in spintronic devices.Comment: 5 pages, 4 figure
The origins of phagocytosis and eukaryogenesis
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Grain boundary energies and cohesive strength as a function of geometry
Cohesive laws are stress-strain curves used in finite element calculations to
describe the debonding of interfaces such as grain boundaries. It would be
convenient to describe grain boundary cohesive laws as a function of the
parameters needed to describe the grain boundary geometry; two parameters in 2D
and 5 parameters in 3D. However, we find that the cohesive law is not a smooth
function of these parameters. In fact, it is discontinuous at geometries for
which the two grains have repeat distances that are rational with respect to
one another. Using atomistic simulations, we extract grain boundary energies
and cohesive laws of grain boundary fracture in 2D with a Lennard-Jones
potential for all possible geometries which can be simulated within periodic
boundary conditions with a maximum box size. We introduce a model where grain
boundaries are represented as high symmetry boundaries decorated by extra
dislocations. Using it, we develop a functional form for the symmetric grain
boundary energies, which have cusps at all high symmetry angles. We also find
the asymptotic form of the fracture toughness near the discontinuities at high
symmetry grain boundaries using our dislocation decoration model.Comment: 12 pages, 19 figures, changed titl
Bias Dependent 1/f Conductivity Fluctuations in Low-Doped LaCaMnO Manganite Single Crystals
Low frequency noise in current biased LaCaMnO single
crystals has been investigated in a wide temperature range from 79 K to 290 K.
Despite pronounced changes in magnetic properties and dissipation mechanisms of
the sample with changing temperature, the noise spectra were found to be always
of the 1/f type and their intensity (except the lowest temperature studied)
scaled as a square of the bias. At liquid nitrogen temperatures and under bias
exceeding some threshold value, the behavior of the noise deviates from the
quasi-equilibrium modulation noise and starts to depend in a non monotonic way
on bias. It has been verified that the observed noise obeys Dutta and Horn
model of 1/f noise in solids. The appearance of nonequilibrium 1/f noise and
its dependence on bias have been associated with changes in the distribution of
activation energies in the underlying energy landscape. These changes have been
correlated with bias induced changes in the intrinsic tunneling mechanism
dominating dissipation in LaCaMnO at low temperatures.Comment: Accepted for publication in the Journal of Applied Physic
MiR221 promotes precursor B-cell retention in the bone marrow by amplifying the PI3K-signaling pathway in mice
Wavelets: mathematics and applications
The notion of wavelets is defined. It is briefly described {\it what} are
wavelets, {\it how} to use them, {\it when} we do need them, {\it why} they are
preferred and {\it where} they have been applied. Then one proceeds to the
multiresolution analysis and fast wavelet transform as a standard procedure for
dealing with discrete wavelets. It is shown which specific features of signals
(functions) can be revealed by this analysis, but can not be found by other
methods (e.g., by the Fourier expansion). Finally, some examples of practical
application are given (in particular, to analysis of multiparticle production}.
Rigorous proofs of mathematical statements are omitted, and the reader is
referred to the corresponding literature.Comment: 16 pages, 5 figures, Latex, Phys. Atom. Nuc
Life at high Deborah number
In many biological systems, microorganisms swim through complex polymeric
fluids, and usually deform the medium at a rate faster than the inverse fluid
relaxation time. We address the basic properties of such life at high Deborah
number analytically by considering the small-amplitude swimming of a body in an
arbitrary complex fluid. Using asymptotic analysis and differential geometry,
we show that for a given swimming gait, the time-averaged leading-order
swimming kinematics of the body can be expressed as an integral equation on the
solution to a series of simpler Newtonian problems. We then use our results to
demonstrate that Purcell's scallop theorem, which states that time-reversible
body motion cannot be used for locomotion in a Newtonian fluid, breaks down in
polymeric fluid environments
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