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Structural analysis of a trimeric assembly of the mitochondrial dynamin-like GTPase Mgm1.

  • Author(s): Yan, Liming;
  • Qi, Yuanbo;
  • Ricketson, Derek;
  • Li, Lei;
  • Subramanian, Kelly;
  • Zhao, Jinghua;
  • Yu, Caiting;
  • Wu, Lijie;
  • Sarsam, Reta;
  • Wong, Melissa;
  • Lou, Zhiyong;
  • Rao, Zihe;
  • Nunnari, Jodi;
  • Hu, Junjie
  • et al.
Abstract

The fusion of inner mitochondrial membranes requires dynamin-like GTPases, Mgm1 in yeast and OPA1 in mammals, but how they mediate membrane fusion is poorly understood. Here, we determined the crystal structure of Saccharomyces cerevisiae short Mgm1 (s-Mgm1) in complex with GDP. It revealed an N-terminal GTPase (G) domain followed by two helix bundles (HB1 and HB2) and a unique C-terminal lipid-interacting stalk (LIS). Dimers can form through antiparallel HB interactions. Head-to-tail trimers are built by intermolecular interactions between the G domain and HB2-LIS. Biochemical and in vivo analyses support the idea that the assembly interfaces observed here are native and critical for Mgm1 function. We also found that s-Mgm1 interacts with negatively charged lipids via both the G domain and LIS. Based on these observations, we propose that membrane targeting via the G domain and LIS facilitates the in cis assembly of Mgm1, potentially generating a highly curved membrane tip to allow inner membrane fusion.

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