On computing pucker free energy profiles, we find that for the GlcNAc ring in sLe x , the triplicate 10 s simulations sample the complete 4 C 1 -to-1 C 4 pucker transition (Figure ); by contrast, the triplicate 1 s simulations fail to sample the 1 C 4 pucker. Given that the 1 s simulations do not sample any non-closed conformations, this difference in sampling of pucker appears to support the hypothesis of Topin et al. that GlcNAc ring puckering is important to the exploration of open conformational states. This is further indicated by a shift in the ring pucker states when moving along the structural path from closed (F 1 ,G 1 ) to the F 2 and G 2 wells (Figure ). The GlcNAc ring primarily occupies a 4 C 1 pucker ( ~ 10°) when in the closed (F 1 ,G 1 ) state;