Structural Properties of CHAPS Micelles, Studied by Molecular Dynamics Simulations

Abstract

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.

The Fluidity of Phosphocholine and Maltoside Micelles and the Effect of CHAPS

“…A rearrangement of the micelles at higher CHAPS concentrations is implied based on the EPR lineshapes and in the 2A zz 0 measurement; however, this rearrangement was not as clear from the central linewidth data. Concentration-dependent structural transitions were previously reported for pure CHAPS micelles (15,19), and shape transitions in binary detergent mixtures were observed when mixing prolate and oblate micelles (9).…”

“…CHAPS is a zwitterionic detergent with a rigid ring structure that may modulate micelle packing and microviscosity. There is a more polar side of the rigid ring system that has three hydroxyl groups that impact how the molecules interact in the micelle (15,19,30). Nonetheless, CHAPS forms micelles, and the rigid ring structure is predicted to modulate the fluidity of the four detergents FC12, FC14, DM, and DDM investigated.…”

“…Reports of micelle microviscosities range from 4 to 50 cP (2-4) depending on the detergent micelle (and ionic strength) and range from 63 to 223 cP for a synthetic 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer depending on the position within the bilayer (2) and $50-140 cP in biological membranes (5). Several scattering (6)(7)(8)(9)(10), spectroscopy (1,(11)(12)(13)(14)(15)(16)(17), and molecular dynamics (18)(19)(20)(21)(22)(23)(24) studies have investigated micelles; however, most of these studies have focused on the micellar structure, polarity or water penetration, and critical micelle concentration rather than chain dynamics. Molecular dynamics studies report that the chain dihedral and CH 2 order parameters in dodecylphosphocholine micelles were comparable to that of the bilayer (24) and that the dihedral transition rate was slower in micelles than that of a DPPC bilayer (24,25).…”

Salt‐induced phase separation of CHAPS and potential application for hydrophobic molecule extraction

“…Furthermore, absorbance‐based assays have a high tolerance to CHAPS due to the absence of a phenyl group . Various studies have been conducted to understand the micelle structure, micellization process and solid phase adsorption properties of CHAPS . However, understanding of CHAPS phase behavior which could extend utility of the detergent to extraction of small organic molecules and proteins via phase separation remains poor …”

Chapter 4 The Results

“…The quaternary amino and sulfonate groups contribute to its zwitterionic character(Rodi et al 2014). The stability of CHAPS and protein molecule were obtained by the interaction of ring hydroxyl group CHAPS with the hydrophobic side chains of proteins(Herrera et al 2014). Though CHAPS is considered as a non-denaturing agent, its ionic nature might cause a change in the ionic state of the proteins and thereby bring changes in the fluorescence properties of the proteins.…”