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.