An allosteric network governs Tom70 conformational dynamics to coordinate mitochondrial import

Area of Science:

• Mitochondrial biology
• Protein import mechanisms
• Structural biology

Background:

• Tom70 facilitates mitochondrial protein import by bridging cytosolic chaperones and the TOM complex.
• The cytosolic domain of human Tom70 (HsTom70c) has N-terminal (NTD) and C-terminal (CTD) domains for chaperone and preprotein binding, respectively.
• The communication mechanism between these domains is not well understood.

Purpose of the Study:

• To elucidate the structural mechanisms underlying HsTom70c function.
• To investigate how ligand binding affects HsTom70c conformation and dynamics.
• To understand the role of interdomain communication in mitochondrial protein import.

Main Methods:

• X-ray crystallography (2.04 Å resolution) of unliganded HsTom70c.
• Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to study conformational dynamics in solution.
• Molecular dynamics (MD) simulations, principal component analysis (PCA), and network analysis.

Main Results:

• The crystal structure revealed two distinct conformations of HsTom70c: open and closed.
• HDX-MS and MD simulations confirmed the existence of these conformations in solution and identified a dynamic continuum between the NTD and CTD.
• Binding of the viral protein Orf9b to the CTD stabilized a partially closed conformation and altered NTD dynamics.

Conclusions:

• HsTom70c exists in multiple conformations linked by an internal dynamic network.
• This network is crucial for coordinating chaperone and preprotein binding.
• Viral protein Orf9b binding disrupts this network, potentially modulating mitochondrial protein import pathways.