Sterol regulatory element-binding protein cleavage-activating protein (SCAP)

Escort protein needed for cholesterol as well as lipid homeostasis. Regulates export of this SCAP/SREBF complicated from the ER upon low cholesterol.

Formation of a ternary complex with INSIG at high sterol concentrations leads to masking of an ER-export signal in SCAP and retention of the complex in the ER. Low sterol concentrations activate release of INSIG, a conformational change in the SSC domain of SCAP, unmasking of the ER export signal, recruitment into COPII-coated vesicles, transfer to the Golgi complex, proteolytic cleavage of SREBF in the Golgi, launch of this transcription factor fragment of SREBF from the membrane, its import into the nucleus and up-regulation of LDLR, INSIG1 and the mevalonate pathway (By similarity).