913 research outputs found
Simulation, Experiment, and Evolution: Understanding Nucleation in Protein S6 Folding
In this study, we explore nucleation and the transition state ensemble of the
ribosomal protein S6 using a Monte Carlo Go model in conjunction with
restraints from experiment. The results are analyzed in the context of
extensive experimental and evolutionary data. The roles of individual residues
in the folding nucleus are identified and the order of events in the S6 folding
mechanism is explored in detail. Interpretation of our results agrees with, and
extends the utility of, experiments that shift f-values by modulating
denaturant concentration and presents strong evidence for the realism of the
mechanistic details in our Monte Carlo Go model and the structural
interpretation of experimental f-values. We also observe plasticity in the
contacts of the hydrophobic core that support the specific nucleus. For S6,
which binds to RNA and protein after folding, this plasticity may result from
the conformational flexibility required to achieve biological function. These
results present a theoretical and conceptual picture that is relevant in
understanding the mechanism of nucleation in protein folding.Comment: PNAS in pres
Principals of the theory of light reflection and absorption by low-dimensional semiconductor objects in quantizing magnetic fields at monochromatic and pulse excitations
The bases of the theory of light reflection and absorption by low-dimensional
semiconductor objects (quantum wells, wires and dots) at both monochromatic and
pulse irradiations and at any form of light pulses are developed. The
semiconductor object may be placed in a stationary quantizing magnetic field.
As an example the case of normal light incidence on a quantum well surface is
considered. The width of the quantum well may be comparable to the light wave
length and number of energy levels of electronic excitations is arbitrary. For
Fourier-components of electric fields the integral equation (similar to the
Dyson-equation) and solutions of this equation for some individual cases are
obtained.Comment: 14 page
High resolution protein folding with a transferable potential
A generalized computational method for folding proteins with a fully
transferable potential and geometrically realistic all-atom model is presented
and tested on seven different helix bundle proteins. The protocol, which
includes graph-theoretical analysis of the ensemble of resulting folded
conformations, was systematically applied and consistently produced structure
predictions of approximately 3 Angstroms without any knowledge of the native
state. To measure and understand the significance of the results, extensive
control simulations were conducted. Graph theoretic analysis provides a means
for systematically identifying the native fold and provides physical insight,
conceptually linking the results to modern theoretical views of protein
folding. In addition to presenting a method for prediction of structure and
folding mechanism, our model suggests that a accurate all-atom amino acid
representation coupled with a physically reasonable atomic interaction
potential (that does not require optimization to the test set) and hydrogen
bonding are essential features for a realistic protein model.Comment: submitted to PNAS 2005-03-1
Electron g-Factor Anisotropy in Symmetric (110)-oriented GaAs Quantum Wells
We demonstrate by spin quantum beat spectroscopy that in undoped symmetric
(110)-oriented GaAs/AlGaAs single quantum wells even a symmetric spatial
envelope wavefunction gives rise to an asymmetric in-plane electron
Land\'e-g-factor. The anisotropy is neither a direct consequence of the
asymmetric in-plane Dresselhaus splitting nor of the asymmetric Zeeman
splitting of the hole bands but is a pure higher order effect that exists as
well for diamond type lattices. The measurements for various well widths are
very well described within 14 x 14 band k.p theory and illustrate that the
electron spin is an excellent meter variable to map out the internal -otherwise
hidden- symmetries in two dimensional systems. Fourth order perturbation theory
yields an analytical expression for the strength of the g-factor anisotropy,
providing a qualitative understanding of the observed effects
Variation in nucleotide homology obtained by amplification, cloning and sequencing of complete S1 gene from field samples of avian infectious bronchitis virus.
Projeto/Plano de Ação: 02.09.01.030
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