Nascent polypeptide-associated complex stimulates protein import into yeast mitochondria

Area of Science:

• Mitochondrial biology
• Protein targeting
• Cellular transport

Background:

• Mitochondria require precise protein import for function.
• Cytosolic factors mediating protein targeting to mitochondria are not fully understood.

Purpose of the Study:

• To identify yeast cytosolic proteins involved in targeting precursor proteins to mitochondria.
• To elucidate the mechanism of nascent chain translocation across mitochondrial membranes.

Main Methods:

• Development of an in vitro import system using purified yeast mitochondria and radiolabeled precursor proteins still attached to ribosomes.
• Analysis of translocation intermediates and the role of salt-released proteins.
• Purification and functional assessment of the nascent polypeptide-associated complex (NAC).

Main Results:

• A translocation intermediate spanning both mitochondrial membranes was generated.
• Mitochondrial membrane potential and surface proteins were essential for import.
• Proteins released from ribosomes by high salt, particularly yeast nascent polypeptide-associated complex (NAC), stimulated import.
• Purified NAC restored import of salt-washed ribosome-bound nascent chains by enhancing productive binding to mitochondria.

Conclusions:

• Ribosome-associated NAC plays a crucial role in facilitating the recognition of nascent precursor proteins by the mitochondrial import machinery.
• NAC acts as a key cytosolic factor in the initial steps of mitochondrial protein targeting.