Organization of Bio-Molecules in Bulk and Over the Nano-Substrate: Perspective to the Molecular Dynamics Simulations (original) (raw)
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Multi-Scale Molecular Dynamics Simulations of a Membrane Protein Stabilizing Polymer
Biophysical Journal, 2011
A positional interpolation/extrapolation method for the mapping of coarse-grained (CG) to atomistic (AT) resolution is presented and tested for single-component micelles formed by lysophospholipids of different chain length. The target CG nanoaggregates were self-assembled from random mixtures of surfactants in explicit MARTINI water and equilibrated by molecular dynamics simulations, at the microsecond time scale. The ambiguity inherent in the definition of the CG particles was explored by mapping the same CG structures to AT resolution surfactants of different size. After the conversion, the obtained AT micelles were simulated for 250 ns and the resulting trajectories were analyzed in detail. The mean lifetime of the surfactant-solvent interactions as well as the lateral diffusion coefficients of the surfactant molecules within the micellar aggregates were obtained for the first time. The results suggest that the individual molecules within the micelle behave like lipids in a fluid membrane. The employed mapping back method is efficient and versatile, as it can be applied to diverse combinations of force fields and systems with a minimum of code development. In a general context, this work illustrates the power of multiscale molecular dynamics simulations for the generation and subsequent examination of self-assembled structures, including the fine characterization of structural and dynamic properties of the resulting aggregate.
Introduction to Molecular Dynamics Simulation
In this chapter a summary is given of the key ingredients necessary to carry out a molecular dynamics simulation, with particular emphasis on macromolecular systems. We discuss the form of the intermolecular potential for molecules composed of atoms, and of non-spherical sub-units, giving examples of how to compute the forces and torques. We also describe some of the MD algorithms in current use. Finally, we briefly refer to the factors that influence the size of systems, and length of runs, that are needed to calculate statistical properties.
Biomacromolecules, 2010
The adsorption of LTP at the decane-water interface was modeled using all-atom and coarse-grained (CG) molecular dynamics simulations. The CG model (300 ns simulation, 1200 ns scaled time) generates equilibrium adsorbed conformations in about 12 h, whereas the equivalent 1200 ns simulation would take about 300 days for the all-atom model. In both models the LTP molecule adsorbs with R-helical regions parallel to the interface with an average tilt angle normal to the interface of 73°for the all-atom model and 62°for the CG model. In the all-atom model, the secondary structure of the LTP is conserved upon adsorption. A considerable proportion of the N-terminal loop of LTP can be found in the decane phase for the all-atom model, whereas in the CG model the protein only penetrates as far as the mixed water-decane interfacial region. This difference may arise due to the different schemes used to parametrize force field parameters in the two models.
Manipulation of biomolecules: A molecular dynamics study
Current Applied Physics, 2014
With the rapid progression of bionanorobotics, manipulation of nano-scale biosamples is becoming increasingly attractive for different biological purposes. Nevertheless, the interaction between a robotic probe and a biological sample is poorly understood and the conditions for appropriate handling is not well-known. Here, we use the molecular dynamics (MD) simulation method to investigate the manipulation process when a nanoprobe tries to move a biosample on a substrate. For this purpose, we have used Ubiquitin (UBQ) as the biomolecule, a single-walled carbon nanotube (SWCNT) as the manipulation probe, and a double-layered graphene sheets as the substrate. A series of simulations were conducted to study the effects of different conditions on the success of the manipulation process. These conditions include the tip diameter, the vertical gap between the tip and substrate, and the initial orientation of the protein. Also we have studied two strategies for the manipulation of the protein by a nano-scale probe that we have named pushing and pulling. Interaction force between carbon nanotube (CNT) tips and the biomolecule, the rootmean-square deviation (RMSD), and the radius of gyration of the protein are monitored for different conditions. We found that larger tip diameters, smaller gaps between tip and substrate, and a pulling strategy increase the chance of a successful manipulation.
Understanding protein adsorption onto solid surfaces is of critical importance in the field of bioengineering, especially for applications such as medical implants, diagnostic biosensors, drug delivery systems, and tissue engineering. This study proposed the use of molecular dynamics simulations with potential of mean force (PMF) calculations to identify and characterize the mechanisms of adsorption of a protein molecule on a designed surface. A set of model systems consisting of a cardiotoxin (CTX) protein and mixed selfassembled monolayer (SAM) surfaces were used as examples. The set of mixed SAM surfaces with varying topographies were created by mixing alkanethiol chains of different lengths. The results revealed that CTX proteins underwent similar conformal changes upon adsorption onto the various mixed SAMs but showed distinctive characteristics in free energy profiles. Enhancement of the adsorption affinity, i.e., the change in free energy of adsorption, for mixed SAMs was demonstrated by using atomic force microscopic measurements. A component analysis conducted to quantify the physical mechanisms that promoted CTX adsorption revealed contributions from both SAMs and the solvent. Further component analyses of thermodynamic properties, such as the free energy, enthalpy, and entropy, indicated that the contribution from SAMs was driven by enthalpy, and the contribution from the solvent was driven by entropy. The results indicated that CTX adsorption was an entropy-driven process, and the entropic component from the solvent, i.e., the hydrophobic interaction, was the major driving force for CTX adsorption onto SAMs. The study also concluded that the surfaces composed of mixtures of SAMs with different chain lengths promoted the adsorption of CTX protein.
A Second Generation Force Field for the Simulation of Proteins, Nucleic Acids, and Organic Molecules
Journal of the American Chemical Society, 1995
We present the derivation of a new molecular mechanical force field for simulating the structures, conformational energies, and interaction energies of proteins, nucleic acids, and many related organic molecules in condensed phases. This effective two-body force field is the successor to the Weiner et al. force field and was developed with some of the same philosophies, such as the use of a simple diagonal potential function and electrostatic potential fit atom centered charges. The need for a 10-12 function for representing hydrogen bonds is no longer necessary due to the improved performance of the new charge model and new van der Waals parameters. These new charges are determined using a 6-31G* basis set and restrained electrostatic potential (RESP) fitting and have been shown to reproduce interaction energies, free energies of solvation, and conformational energies of simple small molecules to a good degree of accuracy. Furthermore, the new RESP charges exhibit less variability as a function of the molecular conformation used in the charge determination. The new van der Waals parameters have been derived from liquid simulations and include hydrogen parameters which take into account the effects of any geminal electronegative atoms. The bonded parameters developed by Weiner et al. were modified as necessary to reproduce experimental vibrational frequencies and structures. Most of the simple dihedral parameters have been retained from Weiner et al., but a complex set of 4 and yj parameters which do a good job of reproducing the energies of the low-energy conformations of glycyl and alanyl dipeptides has been developed for the peptide backbone.
Langmuir, 2010
In order to evaluate the transferability of existing empirical force fields for all-atom molecular simulations of protein adsorption behavior, we have developed and applied a method to calculate the adsorption free energy (ΔG ads ) of model peptides on functionalized surfaces for comparison with available experimental data. Simulations were conducted using the CHARMM program and force field using a host-guest peptide with the sequence TGTG-X-GTGT (where G and T are glycine and threonine amino acid residues, respectively, with X representing valine, threonine, aspartic acid, phenylalanine or lysine) over nine different functionalized alkanethiol self-assembled monolayer (SAM) surfaces with explicitly represented solvent. ΔG ads was calculated using biased-energy replica exchange molecular dynamics to adequately sample the conformational states of the system. The simulation results showed that the CHARMM force-field was able to represent ΔG ads within 1 kcal/ mol of the experimental values for most systems, while deviations as large as 4 kcal/mol were found for others. In particular, the simulations reveal that CHARMM underestimates the strength of adsorption on the hydrophobic and positively charged amine surfaces. These results provide a means for force field evaluation and modification for the eventual development and validation of an interfacial force field for the accurate simulation of protein adsorption behavior.
A new force field for molecular mechanical simulation of nucleic acids and proteins
Journal of the American Chemical Society, 1984
We present the development of a force field for simulation of nucleic acids and proteins. Our approach began by obtaining equilibrium bond lengths and angles from microwave, neutron diffraction, and prior molecular mechanical calculations, torsional constants from microwave, NMR, and molecular mechanical studies, nonbonded parameters from crystal packing calculations, and atomic charges from the fit of a partial charge model to electrostatic potentials calculated by ab initio quantum mechanical theory. The parameters were then refined with molecular mechanical studies on the structures and energies of model compounds. For nucleic acids, we focused on methyl ethyl ether, tetrahydrofuran, deoxyadenosine, dimethyl phosphate, 9-methylguanine-l-methylcytosine hydrogen-bonded complex, 9-methyladenine-1-methylthymine hydrogen-bonded complex, and 1,3-dimethyluracil base-stacked dimer. Bond, angle, torsional, nonbonded, and hydrogen-bond parameters were varied to optimize the agreement between calculated and experimental values for sugar pucker energies and structures, vibrational frequencies of dimethyl phosphate and tetrahydrofuran, and energies for base pairing and base stacking. For proteins, we focused on maps of glycyl and alanyl dipeptides, hydrogen-bonding interactions involving the various protein polar groups, and energy refinement calculations on insulin. Unlike the models for hydrogen bonding involving nitrogen and oxygen electron donors, an adequate description of sulfur hydrogen bonding required explicit inclusion of lone pairs.
Force fields for simulating the interaction of surfaces with biological molecules
Interface focus, 2016
The interaction of biomolecules with solid interfaces is of fundamental importance to several emerging biotechnologies such as medical implants, anti-fouling coatings and novel diagnostic devices. Many of these technologies rely on the binding of peptides to a solid surface, but a full understanding of the mechanism of binding, as well as the effect on the conformation of adsorbed peptides, is beyond the resolution of current experimental techniques. Nanoscale simulations using molecular mechanics offer potential insights into these processes. However, most models at this scale have been developed for aqueous peptide and protein simulation, and there are no proven models for describing biointerfaces. In this review, we detail the current research towards developing a non-polarizable molecular model for peptide-surface interactions, with a particular focus on fitting the model parameters as well as validation by choice of appropriate experimental data.
A positional interpolation/extrapolation method for the mapping of coarse-grained (CG) to atomistic (AT) resolution is presented and tested for single-component micelles formed by lysophospholipids of different chain length. The target CG nanoaggregates were self-assembled from random mixtures of surfactants in explicit MARTINI water and equilibrated by molecular dynamics simulations, at the microsecond time scale. The ambiguity inherent in the definition of the CG particles was explored by mapping the same CG structures to AT resolution surfactants of different size. After the conversion, the obtained AT micelles were simulated for 250 ns and the resulting trajectories were analyzed in detail. The mean lifetime of the surfactant-solvent interactions as well as the lateral diffusion coefficients of the surfactant molecules within the micellar aggregates were obtained for the first time. The results suggest that the individual molecules within the micelle behave like lipids in a fluid membrane. The employed mapping back method is efficient and versatile, as it can be applied to diverse combinations of force fields and systems with a minimum of code development. In a general context, this work illustrates the power of multiscale molecular dynamics simulations for the generation and subsequent examination of self-assembled structures, including the fine characterization of structural and dynamic properties of the resulting aggregate.