The P-loop (see <PDOC00017>) guanosine triphosphatases (GTPases) control a
multitude of biological processes, ranging from cell division, cell cycling,
and signal transduction, to ribosome assembly and protein synthesis. GTPases
exert their control by interchanging between an inactive GDP-bound state and
an active GTP-bound state, thereby acting as molecular switches. The common
denominator of GTPases is the highly conserved guanine nucleotide-binding (G)
domain that is responsible for binding and hydrolysis of guanine nucleotides.
The GB1/RHD3 GTPase family contains a large G domain (~230 amino acids). It is
widespread in eukaryotes, but not detectable in bacteria or archaea. One
conserved subfamily is typified by the Arabidopsis protein root hair defective
3 (RHD3), whose othologs are present in all crown group eukaryotes. The other
subfamily is typified by the interferon γ-induced antiviral GB1 protein
that is conserved in animals. The other GTPases of this subfamily are the
brain finger proteins (BFPs), in which the GTPase domain is combined with an
N-terminal RING finger domain (see <PDOC00449>), which implicates these
proteins in ubiquitin-mediated signaling. Most members of this family have a
large C-terminal, α-helical extension that probably participates in
protein-protein interactions. The GB1/RHD3-type G domain has a low intrinsic
affinity for nucleotide and often depends on nucleotide-dependent
homodimerization to facilitate GTP hydrolysis [1,2,3,4,5,6].
The large GB1/RHD3-type G domain consists of a six-stranded β-sheet
surrounded by eight helices (see <PDB:1DG3>). It contains the conserved
sequence elements of GTP-binding proteins with modifications [2,4,6].
The profile we developed covers the entire GB1/RHD3-type G domain.
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