Structural and functional analysis of MiD51, a dynamin receptor required for mitochondrial fission

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Mitochondrial fission is vital for organelle dynamics, transport, and turnover.
• Dysregulation of mitochondrial fission is implicated in various neurological diseases.
• Dynamin-related protein 1 (Drp1) mediates mitochondrial fission in mammals, requiring recruitment to the organelle.

Purpose of the Study:

• To elucidate the structural basis of MiD51 function in mitochondrial fission.
• To investigate the role of nucleotide binding and other regions of MiD51 in Drp1 recruitment.
• To understand the assembly and dynamics of MiD51 within the mitochondrial fission machinery.

Main Methods:

• X-ray crystallography to determine the structure of human MiD51 cytosolic domain.
• Site-directed mutagenesis to assess the impact of nucleotide binding and other regions on MiD51 function.
• Mitochondrial recruitment assays and live-cell imaging to observe Drp1 and MiD51 dynamics.

Main Results:

• The cytosolic domain of human MiD51 adopts a nucleotidyltransferase fold but lacks catalytic activity.
• MiD51 specifically binds GDP and ADP, though nucleotide binding is not essential for Drp1 recruitment.
• A region outside the nucleotidyltransferase fold is critical for Drp1 recruitment and MiD51 foci formation at mitochondria.
• MiD51 foci formation is Drp1-dependent and these foci are distributed to daughter mitochondria post-fission.

Conclusions:

• MiD51 functions as a scaffold protein in the mitochondrial fission apparatus, independent of its nucleotide-binding capability.
• A distinct region of MiD51, beyond its nucleotidyltransferase-like fold, mediates Drp1 recruitment and fission site assembly.
• MiD51's dynamic behavior and dependence on Drp1 highlight its integral role in the mitochondrial fission process.