Unlike sLe a , triplicate 1 s trajectories only sample closed conformations (F 1 ,G 1 ), with no sampling of neighboring F 2-3 and G 2-3 regions (Figure ). The longer 10 s simulations explore non-closed minima of sLe x , in the F 2-3 and G 2-3 regions, in addition to some infrequent sampling of the G 5 region (Figure ). However, the F 4 and G 4 minima, which tend to be associated with the open protein-bound conformations of the tetrasaccharide, are not sampled, perhaps suggesting that sLe x may be more rigid in solution than sLe a . This potential rigidity is consistent with previous 25 s simulations of sLe x , which similarly did not appear to detect such conformations. As for sLe a , the Neu5Ac23)Gal rotation in sLe x is readily sampled (Figure ).