(B) cGTPase rearrangements in MgGDP binding. Displayed is the MiroS‐MgGDP structure, with select residues from the aligned apo‐MiroS structure shown in orange. GDP is shown as sticks (2Fo‐Fc map, 1.2σ), and Mg2+ as a purple sphere. In the apo state, D505 in the Switch II 503DIDV506 motif is far from the nucleotide‐binding pocket and is hydrogen bonded to R507, which is also stabilized by interactions with P512. In the MgGDP‐bound state, the D505 side‐chain rotates ∼7 Å to interact with the β‐phosphate (arrow), locking the Switch II loop in a β‐strand conformation and extending Gβ3. V506 rotates away from the nucleotide‐binding pocket, and both R507 and Y537 become solvent exposed. cGTPase, C‐terminal GTPase; Sw I/II, Switch I/II; P loop, phosphate‐binding loop. 