InterPro domain: IPR030393

This entry represents the EngB-type G domain.

The P-loop guanosine triphosphatases (GTPases) control amultitude of biological processes, ranging from cell division, cell cycling,and signal transduction, to ribosome assembly and protein synthesis. GTPasesexert their control by interchanging between an inactive GDP-bound state andan active GTP-bound state, thereby acting as molecular switches. The commondenominator of GTPases is the highly conserved guanine nucleotide-binding (G)domain that is responsible for binding and hydrolysis of guanine nucleotides.

Within the translation factor-related (TRAFAC) class of P-loop GTPases, theEngB-type is widespread, but not ubiquitous in all three superkingdoms(missing, for example, from the Crenarchaeota, Caenorhabditis, andDrosophila). Proteins of the EngB-type GTPase family are involved in thebiogenesis of ribosomes and are essential for the survival of a wide range ofbacteria [ 1 , 2 , 3 ].

The EngB-type GTPase is comprised of a central beta-sheet flanked by alpha-helices, in which semi-conserved residues involved innucleotide binding are located in five motifs, called G1-G5. The G1 region(GxxxxGKS) forms the P-loop that is responsible for binding the phosphategroups of the guanine nucleotide. The G2 region corresponds to the switch Iloop, which contains the consensus motif PGxT. The invariant threonine residueis responsible for binding a magnesium ion required for catalysis. The G3region corresponds to the Walker B motif (DxxG), which forms part of switchII. The G4 (TKxD) and G5 motifs are involved in interactions with the guaninemoiety of the substrate [ 4 , 4 ].

1. Classification and evolution of P-loop GTPases and related ATPases. J. Mol. Biol. 317, 41-72
2. Analysis of the open and closed conformations of the GTP-binding protein YsxC from Bacillus subtilis. J. Mol. Biol. 339, 265-78
3. Structure of an essential GTPase, YsxC, from Thermotoga maritima. Acta Crystallogr. Sect. F Struct. Biol. Cryst. Commun. 67, 640-6