Mitochondrial membranes cholesterol translocation

Fig. 8 is a schematic diagram of a cell which shows the known sites in which sterol carrier proteins are involved in cholesterol biosynthesis, utilization and intracellular transfer. SCP, participates in the conversion of squalene to lanosterol and SCP2 participates in the conversion of lanosterol to cholesterol, the conversion of cholesterol to cholesterol ester by ACAT, and probably also in the conversion of cholesterol to 7a-hydroxycholesterol. SCPj transfers cholesterol from cytoplasmic lipid inclusion droplets to mitochondria in the adrenal and SCPj also translocates cholesterol from the outer to the inner mitochondrial membrane. 

Fig. 16. Mitochondrial import of cholesterol. The StAR protein is the major cholesterol (CHOL) carrier bringing the lipid to import sites. The StAR protein is phosphorylated by cyclic AMP-dependent protein kinase (PKA) that is recruited to the mitochondria by the protein PAP7. PAP7 is a binding partner of the peripheral benzodiazepine receptor/translocator protein (TSPO), which forms a complex with the voltage-dependent anion channel (VDAC) and an adenine nucleotide transporter (ANT) at contact sites between the inner and outer mitochondrial membranes. The multiprotein complex constitutes a cholesterol transporter that moves cholesterol from StAR to the inner mitochondrial membrane where the side-chain cleavage enzyme (CYP-11 Al) converts it to pregnenolone (PREG).

---