Mitochondrial AAA-ATPase Msp1 detects mislocalized tail-anchored proteins through a dual-recognition mechanism

Area of Science:

• Mitochondrial biology
• Protein quality control
• Membrane protein targeting

Background:

• The AAA-ATPase Msp1 resides in the outer mitochondrial membrane.
• Msp1 clears mislocalized tail-anchored (TA) proteins, particularly when the guided entry of tail-anchored (GET) pathway is dysfunctional.
• The precise mechanism of Msp1 substrate recognition remains largely unknown.

Purpose of the Study:

• To extensively characterize Msp1 and its substrates.
• To elucidate the molecular mechanisms by which Msp1 recognizes mislocalized TA proteins.
• To understand how Msp1 maintains mitochondrial integrity.

Main Methods:

• Characterization of Msp1 and its known and novel substrates (Pex15Δ30, Pex15, Frt1, Ysy6).
• Analysis of substrate mistargeting and Msp1 recognition mechanisms.
• Mutagenesis studies to identify critical residues in substrates and Msp1.

Main Results:

• Mislocalized TA proteins expose hydrophobic surfaces, which are recognized by Msp1 through conserved hydrophobic residues.
• Introducing hydrophobic patches converts mitochondrial TA proteins into Msp1 substrates.
• Msp1 recognizes basic residues in the inter-membrane space (IMS) domain of substrates via its own acidic D12 residue in the IMS domain.
• A dual-recognition mechanism involving cytoplasmic and IMS domains of Msp1 and substrates facilitates efficient recognition.

Conclusions:

• Msp1 employs a dual-recognition mechanism to identify mislocalized TA proteins based on exposed hydrophobicity and specific charged residues.
• This recognition process is crucial for Msp1's role in maintaining mitochondrial function and protein homeostasis.
• The findings provide significant insights into the specificity and regulation of protein quality control at the mitochondrial surface.