2 research outputs found
Structural Properties of CHAPS Micelles, Studied by Molecular Dynamics Simulations
Detergents
are essential tools to study biological membranes, and
they are frequently used to solubilize lipids and integral membrane
proteins. Particularly the nondenaturing zwitterionic detergent usually
named CHAPS was designed for membrane biochemistry and integrates
the characteristics of the sulfobetaine-type detergents and bile salts.
Despite the available experimental data little is known about the
molecular structure of its micelles. In this work, molecular dynamics
simulations were performed to study the aggregation in micelles of
several numbers of CHAPS (≤18) starting from a homogeneous
water dilution. The force field parameters to describe the interactions
of the molecule were developed and validated. After 50 ns of simulation
almost all the systems result in the formation of stable micelles.
The molecular shape (gyration radii, volume, surface) and the molecular
structure (RDF, salt bridges, H-bonds, SAS) of the micelles were characterized.
It was found that the main interactions that lead to the stability
of the micelles are the electrostatic ones among the polar groups
of the tails and the OH’s from the ring moiety. Unlike micelles
of other compounds, CHAPS show a grainlike heterogeneity with hydrophobic
micropockets. The results are in complete agreement with the available
experimental information from NMR, TEM, and SAXS studies, allowing
the modeling of the molecular structure of CHAPS micelles. Finally,
we hope that the new force field parameters for this detergent will
be a significant contribution to the knowledge of such an interesting
molecule
Molecular Dynamics Study of the Interaction of Arginine with Phosphatidylcholine and Phosphatidylethanolamine Bilayers
In this work, the differential interaction of zwitterionic
arginines
with fully hydrated dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine
(DMPE) bilayers was analyzed by molecular dynamics simulations. In
both systems, arginine binds to lipids with the carboxylate moiety
oriented toward the aqueous phase, in agreement with previous experimental
determinations of ζ potential of DMPC and DMPE liposomes. The
guanidinium groups are found at different depths within the bilayers
indicating that some arginines are buried, especially in DMPE. We
observe, in the DMPE system, that the strongest interaction occurs
between the guanidinium group and the carbonyl oxygen of the lipid.
In the case of DMPC membranes, the strongest interaction is found
between the guanidinium groups of the arginines and the phosphate
groups of the lipids. Unexpectedly, arginine zwitterions are stabilized
through the creation of hydrogen bonds (HB), either with water or
with polar groups of the lipids. The mechanisms of interaction seem
to be different in both membranes. In DMPE bilayers, arginines insert
by breaking the inner HB network of the polar head groups, consequently
increasing the occupied area per lipid molecule. In the DMPC bilayers
the arginines insert by replacing the already present water molecules
within the membrane, without significant effects on the area per lipid