Water orientation inside the constriction region of the AqpM channel . (a) Order parameter . (b) Order parameter . θ is the angle between the unit vector, approximately aligned along the channel axis/membrane normal, nz, and the water dipole vector. Both parameters were measured for each AqpM monomer from 10000 snapshots separated by 2 ps taken from the 20 ns simulation. The black continuous line in each panel represents the average over the 10,000 snapshots and over the four monomers. The error bars represent the standard deviation from the average.