Figure 4.

Ca²⁺ coordination in s2a (a) and s2b (b). Seven O atoms from five residues and one water molecule coordinate to Ca²⁺ in a pentagonal bipyramidal geometry. Pentagonal base interactions are indicated using brown dashes, while axial interactions are indicated using yellow dashes. Residue-to water interactions are indicated with blue dashes. Either one aspartate (s2a) or adjacent serines (s2b) are responsible for positioning the water molecule along the pentagonal base. This figure was prepared using PyMOL (Schrödinger).