Steroidogenic acute regulatory protein (StAR) is a sterol transfer protein.
Steroidogenic acute regulatory protein (StAR) plays a critical role in steroidogenesis by enhancing the delivery of substrate cholesterol from the outer mitochondrial membrane to the cholesterol side chain cleavage enzyme system on the inner membrane. A recombinant StAR protein lacking the first N-terminal 62 amino acid residues that includes the mitochondrial targeting sequence was shown to stimulate the transfer of cholesterol and beta-sitosterol from liposomes to heat-treated mitochondria in a dose-, time-, and temperature-dependent manner. A recombinant mutant StAR protein that cannot stimulate steroidogenesis by isolated mitochondria did not promote sterol transfer. Unlike the more promiscuous lipid transfer protein, sterol carrier protein 2 (SCP2), StAR did not stimulate phosphatidylcholine transfer in our assay system. The recombinant StAR protein increased cholesterol transfer to heat-treated microsomes as well as to heat- and trypsin-treated mitochondria. These observations demonstrate that StAR has sterol transfer activity, which may reflect an ability to enhance desorption of cholesterol from sterol-rich donor membranes. We suggest that the ability of StAR to promote sterol transfer explains its steroidogenic activity.
Center for Research on Reproduction and Women's Health, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104, USA.
C B
CB
Kallen
J T
JT
Billheimer
S A
SA
Summers
S E
SE
Stayrook
M
M
Lewis
J F
JF
Strauss
D000818:Animals; D001692:Biological Transport; D002417:Cattle; D002784:Cholesterol / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008862:Microsomes, Liver / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D000098682:Steroidogenic Acute Regulatory Protein
D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010750:Phosphoproteins; D011994:Recombinant Proteins; D000098682:Steroidogenic Acute Regulatory Protein; D002784:Cholesterol