Structural Basis of Oligomerization in Septin-Like Gtpase of Immunity-Associated Protein 2 (Gimap2)Schwefel, D., Froehlich, C., Eichhorst, J., Wiesner, B., Behlke, J., Aravind, L., Daumke, O.
(2010) Proc Natl Acad Sci U S A 107: 20299
- PubMed: 21059949
- DOI: https://doi.org/10.1073/pnas.1010322107
- Primary Citation of Related Structures:
2XTM, 2XTN, 2XTO, 2XTP
- PubMed Abstract:
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.