STARD3: Lysates

The steroidogenic acute regulatory (StAR) protein facilitates the movement of cholesterol from the outer to inner mitochondrial membrane in adrenal and gonadal cells, fostering steroid biosynthesis. MLN 64 is a 445-amino acid protein of unknown function. When 218 amino-terminal residues of MLN 64 are deleted, the resulting N-218 MLN 64 has 37% amino acid identity with StAR and 50% of StAR's steroidogenic activity in transfected cells. Bacterially expressed N-218 MLN 64 exerts StAR-like activity to promote the transfer of cholesterol from the outer to inner mitochondrial membrane in vitro. The presence of a protease-resistant domain and a protease-sensitive carboxy-terminal domain in N-218 MLN 64 is similar to the organization of StAR. However, as MLN 64 never enters the mitochondria, the protease-resistant domain of MLN 64 cannot be a mitochondrial pause-transfer sequence, as has been proposed for StAR.