46,763 research outputs found
Recommended from our members
Studying Lactoferrin N-Glycosylation.
Lactoferrin is a multifunctional glycoprotein found in the milk of most mammals. In addition to its well-known role of binding iron, lactoferrin carries many important biological functions, including the promotion of cell proliferation and differentiation, and as an anti-bacterial, anti-viral, and anti-parasitic protein. These functions differ among lactoferrin homologs in mammals. Although considerable attention has been given to the many functions of lactoferrin, its primary nutritional contribution is presumed to be related to its iron-binding characteristics, whereas the role of glycosylation has been neglected. Given the critical role of glycan binding in many biological processes, the glycan moieties in lactoferrin are likely to contribute significantly to the biological roles of lactoferrin. Despite the high amino acid sequence homology in different lactoferrins (up to 99%), each exhibits a unique glycosylation pattern that may be responsible for heterogeneity of the biological properties of lactoferrins. An important task for the production of biotherapeutics and medical foods containing bioactive glycoproteins is the assessment of the contributions of individual glycans to the observed bioactivities. This review examines how the study of lactoferrin glycosylation patterns can increase our understanding of lactoferrin functionality
Force-induced misfolding in RNA
RNA folding is a kinetic process governed by the competition of a large
number of structures stabilized by the transient formation of base pairs that
may induce complex folding pathways and the formation of misfolded structures.
Despite of its importance in modern biophysics, the current understanding of
RNA folding kinetics is limited by the complex interplay between the weak
base-pair interactions that stabilize the native structure and the disordering
effect of thermal forces. The possibility of mechanically pulling individual
molecules offers a new perspective to understand the folding of nucleic acids.
Here we investigate the folding and misfolding mechanism in RNA secondary
structures pulled by mechanical forces. We introduce a model based on the
identification of the minimal set of structures that reproduce the patterns of
force-extension curves obtained in single molecule experiments. The model
requires only two fitting parameters: the attempt frequency at the level of
individual base pairs and a parameter associated to a free energy correction
that accounts for the configurational entropy of an exponentially large number
of neglected secondary structures. We apply the model to interpret results
recently obtained in pulling experiments in the three-helix junction S15 RNA
molecule (RNAS15). We show that RNAS15 undergoes force-induced misfolding where
force favors the formation of a stable non-native hairpin. The model reproduces
the pattern of unfolding and refolding force-extension curves, the distribution
of breakage forces and the misfolding probability obtained in the experiments.Comment: 28 pages, 11 figure
Symmetry Breaking of Relativistic Multiconfiguration Methods in the Nonrelativistic Limit
The multiconfiguration Dirac-Fock method allows to calculate the state of
relativistic electrons in atoms or molecules. This method has been known for a
long time to provide certain wrong predictions in the nonrelativistic limit. We
study in full mathematical details the nonlinear model obtained in the
nonrelativistic limit for Be-like atoms. We show that the method with sp+pd
configurations in the J=1 sector leads to a symmetry breaking phenomenon in the
sense that the ground state is never an eigenvector of L^2 or S^2. We thereby
complement and clarify some previous studies.Comment: Final version, to appear in Nonlinearity. Nonlinearity (2010) in
pres
First-principles study of high conductance DNA sequencing with carbon nanotube electrodes
Rapid and cost-effective DNA sequencing at the single nucleotide level might
be achieved by measuring a transverse electronic current as single-stranded DNA
is pulled through a nano-sized pore. In order to enhance the electronic
coupling between the nucleotides and the electrodes and hence the current
signals, we employ a pair of single-walled close-ended (6,6) carbon nanotubes
(CNTs) as electrodes. We then investigate the electron transport properties of
nucleotides sandwiched between such electrodes by using first-principles
quantum transport theory. In particular we consider the extreme case where the
separation between the electrodes is the smallest possible that still allows
the DNA translocation. The benzene-like ring at the end cap of the CNT can
strongly couple with the nucleobases and therefore both reduce conformational
fluctuations and significantly improve the conductance. The optimal molecular
configurations, at which the nucleotides strongly couple to the CNTs, and which
yield the largest transmission, are first identified. Then the electronic
structures and the electron transport of these optimal configurations are
analyzed. The typical tunneling currents are of the order of 50 nA for voltages
up to 1 V. At higher bias, where resonant transport through the molecular
states is possible, the current is of the order of several A. Below 1 V
the currents associated to the different nucleotides are consistently
distinguishable, with adenine having the largest current, guanine the
second-largest, cytosine the third and finally thymine the smallest. We further
calculate the transmission coefficient profiles as the nucleotides are dragged
along the DNA translocation path and investigate the effects of configurational
variations. Based on these results we propose a DNA sequencing protocol
combining three possible data analysis strategies.Comment: 12 pages, 17 figures, 3 table
Simulation studies for surfaces and materials strength
A realistic potential energy function comprising angle dependent terms was employed to describe the potential surface of the N+O2 system. The potential energy parameters were obtained from high level ab-initio results using a nonlinear fitting procedure. It was shown that the potential function is able to reproduce a large number of points on the potential surface with a small rms deviation. A literature survey was conducted to analyze exclusively the status of current small cluster research. This survey turned out to be quite useful in understanding and finding out the existing relationship between theoretical as well as experimental investigative techniques employed by different researchers. Additionally, the importance of the role played by computer simulation in small cluster research, was documented
Computational characterization and prediction of metal-organic framework properties
In this introductory review, we give an overview of the computational
chemistry methods commonly used in the field of metal-organic frameworks
(MOFs), to describe or predict the structures themselves and characterize their
various properties, either at the quantum chemical level or through classical
molecular simulation. We discuss the methods for the prediction of crystal
structures, geometrical properties and large-scale screening of hypothetical
MOFs, as well as their thermal and mechanical properties. A separate section
deals with the simulation of adsorption of fluids and fluid mixtures in MOFs
High Conductance Ratio in Molecular Optical Switching of Functionalized Nanoparticle Self-Assembled Nanodevices
Self-assembled functionalized nano particles are at the focus of a number of
potential applications, in particular for molecular scale electronics devices.
Here we perform experiments of self-assembly of 10 nm Au nano particles (NPs),
functionalized by a dense layer of azobenzene-bithiophene (AzBT) molecules,
with the aim of building a light-switchable device with memristive properties.
We fabricate planar nanodevices consisting of NP self-assembled network
(NPSANs) contacted by nanoelectrodes separated by interelectrode gaps ranging
from 30 to 100 nm. We demonstrate the light-induced reversible switching of the
electrical conductance in these AzBT NPSANs with a record on/off conductance
ratio up to 620, an average value of ca. 30 and with 85% of the devices having
a ratio above 10. Molecular dynamics simulation of the structure and dynamics
of the interface between molecular monolayers chemisorbed on the nano particle
surface are performed and compared to the experimental findings. The properties
of the contact interface are shown to be strongly correlated to the molecular
conformation which in the case of AzBT molecules, can reversibly switched
between a cis and a trans form by means of light irradiations of well-defined
wavelength. Molecular dynamics simulations provide a microscopic explanation
for the experimental observation of the reduction of the on/off current ratio
between the two isomers, compared to experiments performed on flat
self-assembled monolayers contacted by a conducting cAFM tip.Comment: pdf files : publication and supporting informatio
- …