Figure 8
The Glu106 is essential for the activation of GTP hydrolysis. (a and b) View of the nucleotide-binding region. (a) The Irga6 dimer model (Figure 4) is shown (cyan and magenta). The cis interaction between the Glu106 and the γ-phosphate, and the putative trans interactions between the 3'OH and Glu106, as well as between the 3'OH and the γ-phosphate are represented by dotted lines. (b) Two molecules (cyan and magenta) of Irga6 bound to GDP (PDB 1TPZ/A) [14] were adjusted to the Irga6 dimer model, to give the best overlay for the G1, G3, G4 and G5-motifs. The resulting theoretical model of the "Irga6 dimer in the GDP state" is shown. (c) Oligomerisation of 80 μM WT or mutant Irga6 proteins was monitored by light scattering in the presence of 10 mM GTP at 37°C. (d) Hydrolysis of 10 mM GTP (with traces α32P-GTP) was measured in the presence of 80 μM WT or mutant Irga6 proteins at 37°C. Samples were assayed by TLC and autoradiography.