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Beschreibung

Sterol regulatory element-binding protein cleavage-activating protein (UniProt P97260, also known as SCAP, SREBP cleavage-activating protein) is encoded by the SCAP gene (Gene ID 100689048) in hamster species. SCAP is a multi-pass membrane protein with five cytoplasmic domains, eight transmembrane domains, and four lumenal domains. The C-terminal domain of SCAP mediates association with SREBPs, while transmembrane helices 2 6 comprise the sterol-sensing domain that mediates sterol-induced binding of SCAP to Insigs. SCAP is mainly localized in endoplasmic reticulum and Golgi apparatus. It requires the presence of SPRING for proper localization to endoplasmic reticulum. It mediates the activation of membrane-bound transcription factors known as sterol-regulatory element binding proteins (SREBPs) for transcribing genes encoding cholesterol biosynthetic enzymes. Low sterol concentrations are reported to trigger release of Insig and lead to a conformational change in the SSD domain (aa 284-442) of SCAP, unmasking of the ER export signal and promoting recruitment into COPII-coated vesicles and transport of the SCAP-SREBP to the Golgi. In the Golgi, SREBPs are proteolytically processed releasing the transcription factor fragment of SREBPs from the membrane. At high sterol concentrations, formation of a ternary complex with Insig leads to masking of the ER export signal in SCAP, which promotes retention of the complex in the endoplasmic reticulum. (Ref.: Kober, DL., et al. (2020). Proc. Natl. Acad. Sci. USA. 117(45), 28080-28091).