Structure of an essential GTPase, YsxC, from Thermotoga maritima.

YsxC belongs to the YihA family of TRAFAC class GTPases. The protein is involved in the biogenesis of ribosomes and is essential for the survival of a wide range of bacteria. Here, crystal structures of YsxC from Thermotoga maritima and its complex with GDP were determined at maximal resolutions of 2.3 and 1.9 Å, respectively. Major structural differences are observed in the switch I region, which is disordered in the apo form but exists in both an `open' and a `closed' conformation in the GDP-bound state. A comparison with the structure of the GMPPNP-YsxC complex from Bacillus subtilis provides insights into the mechanism of conformational change in the switch I and II regions upon hydrolysis of GTP.