Hello, A change in allocation has been requested: Requester: perezsalas (Ursula Perez Salas) Project: lipidmovement Title: Curvature Effect on the Movement of Lipids Within and Between Membranes Description: We have used coarse-grained simulations utilizing the MARTINI force field to create a unilamellar lipid vesicle, 30nm in diameter, solvated in water consisting of 1M particles. This vesicle size is similar to those used in neutron scattering experiments to which we want to compare the simulations results. In our previous project we calculated the free energy profile of a single lipid (DPPC) across a flat bilayer as well as a vesicle (curved membrane) using the umbrella sampling technique. Our preliminary results show an increase in the energy barrier of lipid flip-flop across the membrane in the curved case compared to the flat bilayer which indicate slower flip-flop rates. We now plan to add cholesterol to the system at extremely low and high concentrations, which will eventually partition into the lipid (DPPC) vesicle. We will then calculate the free energy profile for cholesterol across the bilayer at each concentration and also comparing to the case of a flat membrane. In the Umbrella sampling technique the phase space is divided into many small regions, which are sampled independently and then combined using the Weighted Histogram Analysis method to provide a single energy profile. The umbrella sampling technique allows us to run many short simulations in parallel which are then combined through post-processing. We will use the molecular dynamics program NAMD, which is developed at University of Illinois at Urbana-Champaign and is freely available for download (http://www.ks.uiuc.edu/Research/namd/). NAMD is highly parallel and scales efficiently with the number of particles in the system. Our previous simulations on the Fusion cluster has shown a benchmark of 7ms/timestep on 512 cores. Using a time step of 10fs, we estimate that the proposed calculations require approximately 5 microseconds of simulation requiring a total of 495,000 core-hours. Current: undetermined amount Justification: Requested: 20000 A specific reason has been given: We are near being able to submit a manuscript to a journal and the simulations are close to being completed. Ideally we would not want to stop working on the project for a week, until April 1st. We do anticipate using all the core hours requested within this week. Thank you for your consideration. This needs to be approved and the final allocation amount decided upon. Thank You, The LCRC Accounts System