StAR Recombinant Rabbit Monoclonal Antibody [JE32-23] (HA721469)

UNIPROT #

P49675

PROTEIN NAME

StAR

SYNONYMS

Cholesterol trafficker antibody;Luteinizing hormone induced protein antibody;mitochondrial antibody;Mitochondrial steroid acute regulatory protein antibody;StAR antibody;StAR related lipid transfer (START) domain containing 1 antibody;STAR_HUMAN antibody;StARD1 antibody;START domain containing 1 antibody;START domain containing protein 1 antibody;START domain-containing protein 1 antibody;Steroid acute regulatory protein antibody;Steroidogenic acute regulator antibody;Steroidogenic acute regulatory protein antibody;Steroidogenic acute regulatory protein mitochondrial antibody

SUBCELLULAR LOCATION

Mitochondrion.

FUNCTION

The steroidogenic acute regulatory protein, commonly referred to as StAR (STARD1), is a transport protein that regulates cholesterol transfer within the mitochondria, which is the rate-limiting step in the production of steroid hormones. It is primarily present in steroid-producing cells, including theca cells and luteal cells in the ovary, Leydig cells in the testis and cell types in the adrenal cortex. Cholesterol needs to be transferred from the outer mitochondrial membrane to the inner membrane where cytochrome P450scc enzyme (CYP11A1) cleaves the cholesterol side chain, which is the first enzymatic step in all steroid synthesis. The aqueous phase between these two membranes cannot be crossed by the lipophilic cholesterol, unless certain proteins assist in this process. A number of proteins have historically been proposed to facilitate this transfer including: sterol carrier protein 2 (SCP2), steroidogenic activator polypeptide (SAP), peripheral benzodiazepine receptor (PBR or translocator protein, TSPO), and StAR. It is now clear that this process is primarily mediated by the action of StAR. The mechanism by which StAR causes cholesterol movement remains unclear as it appears to act from the outside of the mitochondria and its entry into the mitochondria ends its function. Various hypotheses have been advanced. Some involve StAR transferring cholesterol itself like a shuttle. While StAR may bind cholesterol itself, the exorbitant number of cholesterol molecules that the protein transfers would indicate that it would have to act as a cholesterol channel instead of a shuttle. Another notion is that it causes cholesterol to be kicked out of the outer membrane to the inner (cholesterol desorption). StAR may also promote the formation of contact sites between the outer and inner mitochondrial membranes to allow cholesterol influx. Another suggests that StAR acts in conjunction with PBR, causing the movement of Cl− out of the mitochondria to facilitate contact site formation. However, evidence for an interaction between StAR and PBR remains elusive.