A dominant negative mitofusin causes mitochondrial perinuclear clusters because of aberrant tethering

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Mitochondrial outer membrane fusion is essential for cellular function and is regulated by mitofusins (Mfn1 and Mfn2).
• Mutations in mitofusin genes are linked to neurodegenerative diseases like Charcot-Marie-Tooth disease type 2A (CMT2A).

Purpose of the Study:

• To investigate the functional consequences of a specific serine-to-proline mutation (S350P in Mfn2, S329P in Mfn1) found in CMT2A patients.
• To elucidate the role of the Hinge 2 domain in mitofusin-mediated membrane fusion.

Main Methods:

• Expression of wild-type and mutant mitofusin variants in cells.
• Mitochondrial morphology and dynamics analysis.
• Biochemical assays to assess mitofusin complex formation and GTPase activity.

Main Results:

• The CMT2A variant mitofusin causes stable mitochondrial tethering and blocks fusion mediated by wild-type mitofusins.
• Mitochondrial clustering induced by the variant requires GTPase domain function and inter-membrane complex formation.
• The S329/S350P substitution disrupts conformational dynamics in Hinge 2, preventing the transition from tethering to fusion.

Conclusions:

• The Hinge 2 domain is critical for regulating the conformational changes necessary for mitochondrial fusion progression.
• Disruption of Hinge 2 dynamics by the CMT2A mutation leads to aberrant mitochondrial tethering and impaired fusion.
• This study proposes a model where Hinge 2 facilitates a power stroke for membrane fusion, which is compromised in CMT2A.