To develop a simulation model for the membrane bound state of h-cisPT, we start by assembling the membrane. We use the symmetric ER model composition determined by Pogozheva and co-workers as the starting point to model the human ER, assembling the system in CHARMM-GUI. This membrane contained a combination of phospholipids, sulfolipids and cholesterol, of varying tail lengths, with the final composition and lipid charge quantified in Table . Each membrane leaflet contained 190 lipids. From this common membrane, six unique simulation systems were constructed by placing a dimer with a DHDDS and a NgBR subunit above the membrane. We simulate the dimer rather than the tetramer here (Fig. ), as pilot simulations indicated that rotational diffusion for the tetramer was very slow relative to achievable simulation timescales. The structure for h-cisPT, without the bound product, was derived from a previously determined X-ray crystallography structure. The protein structure was placed 30 Å above the membrane surface and rotated in increments of 90 degrees such that each of the six simulation systems (replicas) had a different face of the protein oriented towards the membrane (Fig. ). This protocol has been used previously in the literature to arrive at consistent binding orientations for peripheral membrane proteins. A 30Å distance was selected so that the protein would have ample room to rotate before contacting the membrane. After rotation, the system was solvated and ionized using the VMD 27 SOLVATE and AUTOIONIZE tools, called via custom-written python scripts. Following solvation, the system had approximately 200,000 atoms. The final simulation box has dimensions of 10nm by 10nm by 15nm. This size was chosen to permit realistic protein dynamics without periodic boundary effects while optimizing simulation speed.