Molecular Dynamics Simulations of a Membrane Protein-Micelle Complex in Vacuo

We report the first molecular dynamics simulations of an integral membrane protein in a detergent micelle under vacuum conditions. To mimic the dehydration process in electrospray ionization, the N-terminal outer membrane protein A transmembrane domain (OmpA171) from Escherichia coli embedded in a dodecylphosphocholine (DPC) detergent micelle has been simulated with water shells of varying thickness. Removal of the water molecules leaves the membrane protein relatively unaffected by the vacuum conditions. The major structural change occurs in the surrounding micelle, where the DPC molecules structurally rearrange from a normal-phase micelle with DPC detergents radiating spherically from OmpA171 to a structure where the DPC molecules form a layered onion structure in which the head groups, which strive to interact with each other, form an intermediate layer between the inner layer of tail groups that are expelled to the surface, protruding into the void.