Structural insights of human mitofusin-2 into mitochondrial fusion and CMT2A onset

Abstract

Mitofusin-2 (MFN2) is a dynamin-like GTPase that plays a central role in regulating mitochondrial fusion and cell metabolism. Mutations in MFN2 cause the neurodegenerative disease Charcot-Marie-Tooth type 2A (CMT2A). The molecular basis underlying the physiological and pathological relevance of MFN2 is unclear. Here, we present crystal structures of truncated human MFN2 in different nucleotide-loading states. Unlike other dynamin superfamily members including MFN1, MFN2 forms sustained dimers even after GTP hydrolysis via the GTPase domain (G) interface, which accounts for its high membrane-tethering efficiency. The biochemical discrepancy between human MFN2 and MFN1 largely derives from a primate-only single amino acid variance. MFN2 and MFN1 can form heterodimers via the G interface in a nucleotide-dependent manner. CMT2A-related mutations, mapping to different functional zones of MFN2, lead to changes in GTP hydrolysis and homo/hetero-association ability. Our study provides fundamental insight into how mitofusins mediate mitochondrial fusion and the ways their disruptions cause disease.

Defective nucleotide-dependent assembly and membrane fusion in Mfn2 CMT2A variants improved by Bax

“…BDLP also exists in an extended conformation in the presence of lipid and GMPPNP (PDB 2W6D) and using this model, A383 is predicted to be in a helix of HB1 with S378 ( Fig 1B). In a recently published structure of truncated human Mfn2, all four positions are located in α helix 3 of HB1, adjacent to the truncation site where the N terminus stops and is linked to a C-terminal helix ( Fig S1) (Li et al, 2019). Therefore, these positions are likely to be in a conformationally dynamic region proximal to or within hinge 1.…”

“…The results presented here are consistent with BDLP-based structural models that suggest this region functions as a hinge. The recently published structure of truncated human Mfn2 raises the intriguing possibility that these four amino acids could also be positioned in a continuous helix (α helix 3) adjacent to the predicted hinge (Li et al, 2019). The integrity of this helix could also be important to support conformational changes in the context of the full-length protein.…”

Mitofusin 2 Dysfunction and Disease in Mice and Men

“…Yet, detailed structures of individual mitofusin proteins located on outer mitochondrial membranes, of the oligomeric MFN structures that presumably mediate membrane deformation required for membrane fusion, and of trans MFN-MFN dimers that extend outward from mitochondria into cytosolic space and tether mitochondria together, are currently lacking. Consequently, much of the structural information about MFNs and the macromolecular complexes they form is either hypothetical or inferential (Koshiba et al, 2004;Brandt et al, 2016;Franco et al, 2016;Mattie et al, 2018;Rocha et al, 2018;Li et al, 2019).…”

Mitochondrial Surveillance by Cdc48/p97: MAD vs. Membrane Fusion

“…While the precise mechanism allowing mitofusins to perform OMM fusion remains elusive, structural insights in the last years gave extremely valuable hints to elucidate the events leading to membrane merging [198][199][200][201]. Structures of the mitofusin homologue bacterial dynamin-like protein (BDLP) revealed two different conformations, depending on the nucleotide state [202,203].…”

“…Upon approximation of two mitochondria, mitofusins physically interact, allowing trans tethering to occur [213][214][215]. This depends on interactions between the GTPase domains (G-G interface) [199][200][201]. Subsequently, mitofusins undergo higher oligomerization [211,216].…”