Investigating Cholesterol Dynamics and Interactions with the Dopamine Transporter using a Membrane Mimetic Model

Abstract

Cholesterol, an integral component of animal lipid membranes, is involved in modulation of both membrane physical properties and a wide variety of membrane proteins. Conventional computational studies of cholesterol-protein interactions have been either using coarse-grained methods or relying on > μs all-atom simulations due to the slow dynamics of lipids, in order to provide useful information. The highly mobile membrane-mimetic (HMMM) model has been previously reported to study interactions between peripheral membrane proteins and phospholipids with expedited lipid reorganization. Here, we have extended the use of the HMMM model to investigate interactions between integral membrane protein and cholesterol. Cholesterol dynamics were first closely examined in the HMMM model with extensive all-atom molecular dynamics simulations. Both lateral diffusion and flip-flop motion were shown to be significantly accelerated at cholesterol concentrations ranging from 5% to 50%, while atomic density profiles and internal dynamics of cholesterols with proper restraints in the HMMM membranes were found similar to those in full-length lipid membranes. The HMMM model was then applied to study cholesterol interactions with an integral membrane protein, dopamine transporter. The cholesterol binding sites and detailed interactions with the dopamine transporter observed in the HMMM membrane were compared with those from microsecond all-atom molecular dynamics simulations and experimental data. Our results show great potential and advantages of using the HMMM model to identify cholesterol binding sites with enhanced efficiency and clarify cholesterol-protein interactions without losing atomic details.