Structural basis of oligomerization in septin-like GTPase of immunity-associated protein 2 (GIMAP2).
GTPases of immunity-associated proteins (GIMAPs) are a distinctive family of GTPases, which control apoptosis in lymphocytes and play a central role in lymphocyte maturation and lymphocyte-associated diseases. To explore their function and mechanism, we determined crystal structures of a representative member, GIMAP2, in different nucleotide-loading and oligomerization states. Nucleotide-free and GDP-bound GIMAP2 were monomeric and revealed a guanine nucleotide-binding domain of the TRAFAC (translation factor associated) class with a unique amphipathic helix α7 packing against switch II. In the absence of α7 and the presence of GTP, GIMAP2 oligomerized via two distinct interfaces in the crystal. GTP-induced stabilization of switch I mediates dimerization across the nucleotide-binding site, which also involves the GIMAP specificity motif and the nucleotide base. Structural rearrangements in switch II appear to induce the release of α7 allowing oligomerization to proceed via a second interface. The unique architecture of the linear oligomer was confirmed by mutagenesis. Furthermore, we showed a function for the GIMAP2 oligomer at the surface of lipid droplets. Although earlier studies indicated that GIMAPs are related to the septins, the current structure also revealed a strikingly similar nucleotide coordination and dimerization mode as in the dynamin GTPase. Based on this, we reexamined the relationships of the septin- and dynamin-like GTPases and demonstrate that these are likely to have emerged from a common membrane-associated dimerizing ancestor. This ancestral property appears to be critical for the role of GIMAPs as nucleotide-regulated scaffolds on intracellular membranes.
Max-Delbrück-Centrum für Molekulare Medizin, Kristallographie, Robert-Rössle-Strasse 10, 13125 Berlin, Germany.
David
D
Schwefel
Chris
C
Fröhlich
Jenny
J
Eichhorst
Burkhard
B
Wiesner
Joachim
J
Behlke
L
L
Aravind
Oliver
O
Daumke
D002151:Calorimetry; D002851:Chromatography, High Pressure Liquid; D003460:Crystallization; D019281:Dimerization; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D019169:Jurkat Cells; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D016296:Mutagenesis; D009711:Nucleotides / Q000378:metabolism; D010802:Phylogeny; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014461:Ultracentrifugation
D008565:Membrane Proteins; D009711:Nucleotides; C553225:GIMAP2 protein, human; D020558:GTP Phosphohydrolases