The structural basis of the TIM10 chaperone assembly.

Area of Science:

• Mitochondrial biogenesis
• Protein import and folding
• Structural biology

Background:

• Tim9 and Tim10 are essential "small Tim" proteins facilitating polytopic protein insertion into the inner mitochondrial membrane.
• These proteins are imported from the cytosol and assembled in the intermembrane space, but their conformational properties and the structure of the TIM10 complex are poorly understood.

Purpose of the Study:

• To characterize the structural properties of Tim9 and Tim10 proteins in free and assembled states.
• To determine the first three-dimensional structure of the TIM10 complex.
• To elucidate the mechanism of small Tim protein assembly and function.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy
• Circular Dichroism (CD)
• Small Angle X-ray Scattering (SAXS)
• Ab initio shape reconstruction

Main Results:

• Free Tim9 and Tim10 proteins exist as unfolded chains in reduced states and molten globules in oxidized states.
• Only oxidized Tim9 and Tim10 proteins can form the TIM10 complex.
• The first low-resolution 3D structure of the TIM10 complex was determined, revealing extensive surface hydrophobicity.
• Zinc binding stabilizes the reduced state but does not significantly alter secondary structure.

Conclusions:

• The study elucidates the conformational changes and assembly requirements of the Tim9-Tim10 complex.
• The determined structure provides insights into the chaperone function of the TIM10 complex in mitochondrial protein insertion.
• Oxidation is a critical factor for the assembly and function of small Tim proteins.