An allosteric network governs Tom70 conformational dynamics to coordinate mitochondrial protein import

Area of Science:

• Mitochondrial biology
• Structural biology
• Molecular mechanisms of protein import

Background:

• Tom70 is essential for mitochondrial protein import, mediating preprotein transfer from chaperones to the TOM complex.
• The human Tom70 cytosolic domain (HsTom70c) has N-terminal (NTD) and C-terminal (CTD) domains, but the linkage mechanism is unclear.

Purpose of the Study:

• To elucidate the structural basis of Tom70 function and allostery.
• To understand how viral proteins interact with and modulate Tom70 activity.

Main Methods:

• X-ray crystallography of unliganded HsTom70c at 2.04 Å resolution.
• Hydrogen-deuterium exchange mass spectrometry (HDX-MS) and molecular dynamics (MD) simulations.
• Principal component and dynamical network analyses.

Main Results:

• Revealed two distinct conformations (open and closed) of HsTom70c in the crystal structure, stabilized by interdomain contacts and present in solution.
• Identified a dynamic continuum linking the NTD and CTD, involving specific helical regions.
• Demonstrated that viral protein Orf9b binding to the CTD stabilizes an intermediate conformation and disrupts the NTD-CTD dynamic network.

Conclusions:

• The study provides the first structural insights into Tom70 allostery, revealing a dynamic interplay between its functional domains.
• Findings offer a framework for understanding Tom70's role in chaperone binding, protein import, and viral interference.
• The structure-function relationship elucidated here is key to understanding mitochondrial import regulation.