In fact, the average number of water molecules in the pockets strongly correlates with the orientation of Loop C, which caps the binding site upon glycine binding and opens upon unbinding or in the absence of glycine. Upon entering the pocket, glycine interacts with Loop C and drags it towards the binding pocket, as also shown in other Cys-loop receptor simulations, resulting in a contraction of the pocket. The orientation of Loop C was monitored through the angle shown in Figure ii) and described in the Methods section; results for all the models are shown in Figure ii); the time-evolution can be found in the Supporting Information, Figure As a homomeric pLGIC, the GlyR has five subunits symmetrically assembled around the axis of the ion channel. The ligands at subunits interfaces may induce competing push and pull interactions. The fact that the subunits are five, an odd number, may produce some degree of frustration, possibly making the two-ligand systems with non-consecutive occupation more suitable for binding site contraction and favourable binding. The alternate pattern of the orientation angle of Loop C and water content in the pockets of the Apo model, as well as in the ligated systems, suggest that there may be synergistic interactions among subunits. However, correlation between the state of "openness" of the Loop C of different pockets is not straightforward to demonstrate. For example, the Loop C orientation angle of each pocket was correlated to that of the adjacent pocket and quantified with the Pearson correlation coefficient, as shown in Figure iv. The values are overall small and do not seem to show clear patterns; they, however, only assess the fluctuations and whether the Loop C angles of adjacent subunits tend to increase or decrease simultaneously, rather than the propensity of the pockets to be more or less open.