Fig. 1

MglA has a three-state GDP/GTP switch. a Schematic representation of the GDP-bound, GTP-bound and mixed MglA conformations. The inactive conformations of the switch regions are in red, the active conformations are in green. The phosphates of GDP, GTP and Pi are depicted as yellow spheres. b Structure of MglA-GDP. The switch 1 is retracted and switch 2 has an autoinhibitory conformation. c Close-up view of nucleotide-binding site of MglA-GDP. The arginine finger is remote from the nucleotide and Pro80 and Gly81 from switch 2 occlude the Mg²⁺ and γ-phosphate-binding sites. d Structure of MglA-GTPγS-Mg²⁺. Switch 1 and switch 2 have active conformations. e Close-up view of the nucleotide-binding site in MglA-GTPγS. The arginine finger is remote from the nucleotide and Mg²⁺ has an incomplete coordination sphere. f Overlay of switch 1 from MglA-GDP, MglA-GTPγS and the mixed MglA form (see Fig. 1g, h for this form). The twisted three-residue shift in the GTPγS-bound form is highlighted by the positions of F56 and F59. Note the flexibility of switch 1 loop. g Overlay of switch 2 in MglA-GDP, MglA-GTPγS and the mixed MglA form, showing the large difference near Gly 81. Only GTPγS is shown for clarity. h The mixed MglA form features a retracted switch 1 and an active switch 2 conformations. The structure contains GDP and a phosphate or sulfate. i Close-up view of the nucleotide-binding site of the mixed MglA form. The partially occupied phosphate/sulfate positions are shown. j The mixed MglA form can accommodate GTP. Overlay of GTPγS taken from the MglA-GTPγS structure onto the mixed MglA structure. The surface of the nucleotide-binding site is shown as a surface, with the retracted switch 1 in pink and the active switch 2 in green. Color-coding for all panels except (a) and (j)  is: GDP-bound: pink; GTPγS-bound: green; mixed form: blue. Hydrogen bonds are shown as dotted lines. Mg²⁺ is shown in beige. Sw1: switch 1. Sw2: switch 2.