Umbrella sampling calculations. One-dimensional potential of mean force (PMF) profiles were computed using umbrella sampling along the angles of the Fucα(14)GlcNAc and Galβ(13)GlcNAc glycosidic linkages of sLe a , denoted  F and  G respectively (Figure ). A total of 120 window simulations along each torsion were computed, subjected to a harmonic biasing force of 200 kcal mol -1 rad -2 . Distinct from the other enhanced sampling simulations in this work, a 1 fs time step was used to improve stability. The systems were equilibrated using the equilibration protocol above, and then each window, under the influence of its respective biasing potential, was subject to an additional 500000 steps of energy minimization and 1 ns of NVT equilibration prior to 20 ns of NVT production dynamics, recording dihedral values every 50 steps.