Structural basis for GTP hydrolysis and conformational change of MFN1 in mediating membrane fusion

Area of Science:

• Mitochondrial biology
• Molecular and structural biology
• Cellular dynamics

Background:

• Mitochondrial outer membrane fusion is essential for cellular function.
• Mitofusins (MFNs) are key GTPases mediating this process.
• Dysfunctional MFNs are linked to Charcot-Marie-Tooth neuropathy type 2A (CMT2A).

Purpose of the Study:

• Determine the structure of the human MFN1 GTPase domain.
• Elucidate the mechanism of MFN1-mediated membrane fusion.
• Understand how CMT2A mutations affect MFN1 function.

Main Methods:

• X-ray crystallography to determine the structure of MFN1's minimal GTPase domain (MGD) with GDP-BeF3-.
• Biochemical assays to study GTP hydrolysis.
• In vitro assays and cell-based rescue experiments using MFN1-deleted cells.

Main Results:

• The MFN1 MGD forms a dimer with a canonical GTPase fold and an associated four-helix bundle (HB1).
• A potassium ion is crucial for GTP hydrolysis by MFN1.
• A conformational change in the HB1 structure suggests a mechanism for pulling membranes together during fusion.
• The findings explain how CMT2A mutations impair MFN-mediated fusion.

Conclusions:

• The structure of MFN1 provides insights into the molecular mechanism of mitochondrial fusion.
• Potassium-dependent GTP hydrolysis and HB1 conformational changes are critical for MFN1 function.
• This work clarifies the molecular basis of MFN dysfunction in CMT2A.