Computer simulation of nanoparticles translocation through phospholipid membranes within single chain mean field approach

Las células biológicas, bloques elementales de construcción de la materia viva, son presentadas en grandes cantidades en nuestro planeta, y son extremadamente importantes para nosotros, porque todos estamos hechos de ellos. Un componente esencial de cada célula es la membrana celular, protegiendo las células del medio ambiente y también controlando el transporte de los productos químicos entre el interior y el exterior de la célula. Cuando un extraño nano-objeto se aproxima a la membrana celular, las preguntas importantes sobre su destino surgirán de manera natural. ¿Será el nano-objeto capaz de atravesar la membrana, o la membrana lo parará? ¿Si la nano-objeto dañará seriamente los mecanismos de membrana, provocando el muerte de la célula, o no? Alguien puede imaginar numerosas aplicaciones prácticas de las interacciones específicas posibles entre un nano-objeto y la membrana. Pueden ser utilizadas, por ejemplo, para entregar una medicina necesaria dentro de una célula enferma, o para eliminar las células dañinas específicas por la destrucción de sus membranas o por la supresión de su correcto funcionamiento. Las preguntas mencionadas anteriormente son difíciles de responder en la actualidad, tanto por los métodos experimentales como por los métodos teóricos. La mayor dificultad es la compleja estructura de la membrana celular, que consiste de una bicapa lipídica, con numerosas proteínas integradas en él y ancladas a ella. La base de lípidos de la membrana está formada por una mezcla de fosfolípidos, glucolípidos, colesterol, y los fosfolípidos son el principal compuesto de la bicapa. Así, una bicapa de fosfolípidos puros puede ser considerada como un modelo de una membrana de la célula real, tanto en estudios experimentales como en unos teóricos. Se puede utilizar para estimar las propiedades mecánicas de la membrana biológica, su permeabilidad para diferentes productos químicos y nano-objetos, para estudiar su interacción con las proteínas individuales. El número de los métodos experimentales se aplican con éxito paraBiological cells, elementary building blocks of the live matter, are presented in large amounts on our planet, and they are extremely important for us, because all we are made of them. An essential component of every cell is the cell membrane, protecting the cell from the environment and also controlling the transport of chemicals between the interior and exterior of the cell. When an extraneous nano-object approaches the cell membrane, important questions about their destiny arise naturally. Will be the nano-object able to pass through the membrane, or will the membrane stop it? Will the nano-object severely damage the membrane machinery, causing the cell death, or not? One can image numerous practical applications of specific interactions possible between a nano-object and the membrane. They may be used, for example, to deliver a necessary medicine inside a deceased cell, or to kill some specific harmful cells by destruction of their membranes or by suppression of their proper functioning. The questions outlined above are hard to answer at the present day, both using experimental or theoretical methods. The major difficulty is the complex structure of the cell membrane, consisting of lipid bilayer, with numerous proteins embed into it and anchored to it. The lipid basement of the membrane is formed by mixture of phospholipids, glycolipids, cholesterol, and the phospholipids are the major compound of the bilayer. Thus a pure phospholipid bilayer can be considered as a model of a real cell membrane both in experimental and theoretical studies. It can be used to estimate mechanical properties of the biological membrane, its permeability for different chemicals and nano-objects, to study its interaction with single proteins

General model of phospholipid bilayers in fluid phase within the single chain mean field theory

Coarse-grained model for saturated (DCPC, DLPC, DMPC, DPPC, DSPC) and unsaturated (POPC, DOPC) phospholipids is introduced within the Single Chain Mean Field theory. A single set of parameters adjusted for DMPC bilayers gives an adequate description of equilibrium and mechanical properties of a range of saturated lipid molecules that differ only in length of their hydrophobic tails and unsaturated (POPC, DOPC) phospholipids which have double bonds in the tails. A double bond is modeled with a fixed angle of 120 degrees, while the rest of the parameters are kept the same as saturated lipids. The thickness of the bilayer and its hydrophobic core, the compressibility and the equilibrium area per lipid correspond to experimentally measured values for each lipid, changing linearly with the length of the tail. The model for unsaturated phospholipids also fetches main thermodynamical properties of the bilayers. This model is used for an accurate estimation of the free energies of the compressed or stretched bilayers in stacks or multilayers and gives reasonable estimates for free energies. The proposed model may further be used for studies of mixtures of lipids, small molecule inclusions, interactions of bilayers with embedded proteins

Biomolecule surface patterning may enhance membrane association

Under dehydration conditions, amphipathic Late Embryogenesis Abundant (LEA) proteins fold spontaneously from a random conformation into alpha-helical structures and this transition is promoted by the presence of membranes. To gain insight into the thermodynamics of membrane association we model the resulting alpha-helical structures as infinite rigid cylinders patterned with hydrophobic and hydrophilic stripes oriented parallel to their axis. Statistical thermodynamic calculations using Single Chain Mean Field (SCMF) theory show that the relative thickness of the stripes controls the free energy of interaction of the alpha-helices with a phospholipid bilayer, as does the bilayer structure and the depth of the equilibrium penetration of the cylinders into the bilayer. The results may suggest the optimal thickness of the stripes to mimic the association of such protein with membranes.Comment: Published in ACS Nano http://pubs.acs.org/doi/pdf/10.1021/nn204736

Integration Project: the Great Silk Road (the History of Creation)

In article questions of history of creation of the Great Silk way are considered. Conditions for development of integration process are analyzed. The conclusion is drawn that Great the Silk way became a link between the East and the West and played a big role in forming of cultural, commercial and political connections between the people