Figure 2. Tsr1 lacks a functional GTPase active site.

(a) Comparison of Tsr1 with the crystal structure of EF-Tu in the GTP-bound state (PDBid 1exm). A cartoon representation of Tsr1 is shown superposed with EF-Tu in grey on the left, while a cartoon structure of EF-Tu is shown in the same orientation on the right. EF-Tu domains I–III are coloured blue, teal and green, respectively. The GTP analogue GMPPNP is shown as sticks. (b) A close-up view of the active site of EF-Tu (right) and the equivalent site of Tsr1 with GMPPNP from EF-Tu superposed. Clashes between GMPPNP and Tsr1 are indicated with arrows (left). Sequences for characteristic motifs of GTPases are shown underneath, derived from a structure-based sequence alignment. In both sequence and structures, switch I is black, switch II is wheat and the P-loop is grey.