Encapsulation of myoglobin in a cetyl trimethylammonium bromide micelle in vacuo: a simulation study

A recently published paper describes encapsulation of myoglobin into cetyl trimethylammonium bromide (CTAB) micelles by electrospray ionization followed by detection using mass spectrometry [Sharon, M., et al. (2007) J. Am. Chem. Soc. 129, 8740-8746]. Here we present molecular dynamics simulations aimed at elucidating the structural transitions that accompany the encapsulation and dehydration processes. Myoglobin associates with CTAB surfactants in solution, but no complete reverse micelle is formed. Upon removal of most of the water and exposure of the system to vacuum, a stable protein-surfactant reverse micelle forms. The surfactants shield the protein to a large extent from dehydration-related conformational changes, in the same manner that a water shell does, as previously described by Patriksson et al. [(2007) Biochemistry 46, 933-945]. Solvated CTAB micelles undergo a rapid inversion when transported to the gas phase and form very stable reverse micelles, independent of the amount of water present.