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Membrane Transport
Eukaryotes
Mitochondrial Protein Import
Targeting and translocation of nuclear-encoded proteins into mitochondria.
Overview
~99% of mitochondrial proteins are nuclear-encoded and must be imported. The TOM complex (outer membrane) recognizes mitochondrial targeting sequences (MTS). TIM23 imports matrix and inner membrane proteins, while TIM22 handles carrier proteins. The SAM complex inserts β-barrel proteins into the outer membrane. The MIA pathway imports small IMS proteins. Import requires the mitochondrial membrane potential and ATP-driven Hsp70 (mtHsp70/mortalin).
Cellular Location
Outer and inner mitochondrial membranes
Clinical Significance
Defects cause mitochondrial diseases; import efficiency declines with age; some cancer drugs exploit import machinery; essential for mitochondrial biogenesis.