Pannexin is the major ATP release channel in humans. Experimental evidence suggests that phosphorylation is a major factor in activating the channel. The channel undergoes a change from a small pore into a large pore conformation. The latter is permeable to ATP. Up to date there are 7 structures of the channel. There is controversy what the open pore structure is. Most of those structures have a gate too small for ATP to pass. We solved the structure of completely dephosphorylated pannexin and phosphorylated pannexin. From the first models it appears as if a slight tilt in the helix containing the gate causes the gating tryptophan to adopt a completely new conformation. The goal of the proposal is exploratory. We are interested to explore the possible rotamers of that tryptophan and an arginine that forms a pi-interaction. With this we will know if there are preferred conformation of that sidechain. We are in the process of solving the structures of mutants and supplement MD data with electrophysiological measurements. The outcome of this preliminary study will be important for a grant application.