Figure 5: Mechanism of nucleotide exchange by Mon1–Ccz1.

(a) Superposition of ScYpt7 bound to the GTP analogue GNP in magenta with MC1-bound CtYpt7 in blue. The switch I and switch II regions, which undergo major rearrangements, are labelled. (b) Interaction of F33 and Y37 from switch I of Ypt7 with two hydrophobic pockets on MC1. The surface of MC1 is coloured according to hydrophobicity from green (hydrophilic) to grey (hydrophobic). (c) Nucleotide exchange rates of CtYpt7 wild type and the mutants F33A and K38A are plotted as a function of the concentration of CtMC1core. Error bars represent s.d. of three independent biological repeats. (d) Close-up of the nucleotide pocket from ScYpt7-GNP and MC1-bound CtYpt7. The position of switch II D63/64 and P-loop K21 are unaltered. K38 from switch I is inserted into the pocket and clashes with the Mg2+ involved in coordinating nucleotides.