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Domain structure and lipid interaction of recombinant yeast Tim44
C Weiss1, W Oppliger, G Vergères
1Department of Biochemistry, Tel-Aviv University, Tel-Aviv 69978, Israel.
Summary
Tim44 anchors the mitochondrial protein import motor to the inner membrane. This protein interacts with cardiolipin-containing membranes via electrostatic forces and head group penetration.
Area of Science:
- Mitochondrial biology
- Protein translocation
- Membrane biophysics
Background:
- Tim44 is crucial for protein import into mitochondria.
- It anchors the motor complex involving mitochondrial 70-kDa heat-shock protein (mhsp70) and mGrpE.
- Understanding Tim44's membrane interaction is key to elucidating the import mechanism.
Purpose of the Study:
- To investigate the biophysical properties of Tim44.
- To determine how Tim44 interacts with mitochondrial inner membrane lipids.
- To understand the anchoring mechanism of the protein import motor.
Main Methods:
- Overexpression and purification of Tim44 in E. coli.
- Limited proteolysis and analytical ultracentrifugation.
- Liposome and phospholipid monolayer binding assays.
Main Results:
- Tim44 is an elongated monomer with a stable C-terminal domain.
- Tim44 binds strongly to cardiolipin-containing liposomes but weakly to phosphatidylcholine liposomes.
- Binding involves electrostatic interactions and penetration of the lipid head group region.
Conclusions:
- Tim44 anchors the mitochondrial protein import motor through specific lipid interactions.
- Cardiolipin is important for strong Tim44 membrane association.
- Tim44 utilizes both electrostatic and insertion mechanisms for membrane binding.