InterPro domain: IPR030394

This entry represents the HflX-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[ 1 , 2 , 3 ].

Within the translation factor-related (TRAFAC) class of P-loop GTPases, theHflX-type is a widely distributed family of GTPases that interact with thelarge ribosomal subunit. The broad phylogenetic distribution pattern of HflXGTPases in Bacteria, Archaea, and Eukaryotes (including human) suggests abasic cellular function for this protein family.

The HflX-type G domain is composed of six beta-strands and five alpha-helices [ 4 ]. It consists of the following conserved sequence motifs:the G1 motif (or P-loop), consensus GX4GK(S/T), which is responsible forinteracting with the alpha and beta-phosphates of nucleotide di- andtriphosphates; the G2 variable effector loop (DXnT); the G3 motif (DX2G),which interacts with the gamma-phosphate of nucleotide triphosphates; and theG4 motif (NKXD), which conveys specificity for guanine nucleotides throughhydrogen bonding to the base [ 4 ].

1. Classification and evolution of P-loop GTPases and related ATPases. J. Mol. Biol. 317, 41-72
2. Structure of the ribosome associating GTPase HflX. Proteins 78, 705-13
3. Toward understanding the function of the universally conserved GTPase HflX from Escherichia coli: a kinetic approach. Biochemistry 48, 10793-802