InterPro domain: IPR006703

This entry represents the AIG1-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.

The TRAFAC (translation factor related) class AIG1/Toc34/Toc159-likeparaseptin GTPase family contains the following subfamilies [ 1 ]:

• The GTPases of immunity-associated protein (GIMAP)/immune-associated nucleotide-binding protein (IAN) subfamily is conserved among vertebrates and angiosperm plants and has been postulated to regulate apoptosis, particularly in context with diseases such as cancer, diabetes, and infections. The function of GIMAP/IAN GTPases has been linked to self defense in plants and to the development of T cells in vertebrates [ 2 , 3 ].
• Plant-specific Toc (translocon at the outer envelope membrane of chloroplasts) proteins. Toc proteins function as integral components of the chloroplast protein import machinery. The Toc translocon contains the two membrane-bound GTPases Toc33/34 and Toc 159, which expose their G domains to the cytosol and recognise and then deliver precursor proteins through the translocation pore Toc75 [ 4 , 5 ].

The GIMAP/IAN GTPases contain a avrRpt2 induced gene 1 (AIG1)-type G domainthat exhibits the five motifs G1-G5 characteristic for GTP/GDP-bindingproteins. In addition, the AIG-type G domain contains a unique, highlyconserved, hydrophobic motif between G3 and G4. It has a divergent version ofthe guanine recognition motif (G4) at the end of the core strand 5 and anadditional helix alpha6 at the C terminus. The AIG1-type G domain contains acentral beta-sheet sandwiched by two layers of alpha-helices.

1. Classification and evolution of P-loop GTPases and related ATPases. J. Mol. Biol. 317, 41-72
2. Comparative analysis of the human gimap gene cluster encoding a novel GTPase family. Gene 341, 291-304
3. Structural basis of oligomerization in septin-like GTPase of immunity-associated protein 2 (GIMAP2). Proc. Natl. Acad. Sci. U.S.A. 107, 20299-304
4. Dimerization is important for the GTPase activity of chloroplast translocon components atToc33 and psToc159. J. Biol. Chem. 282, 13845-53
5. The GTPase cycle of the chloroplast import receptors Toc33/Toc34: implications from monomeric and dimeric structures. Structure 16, 585-96