SREBP cleavage-activating protein

SREBP cleavage-activating protein (SCAP) is a protein that in humans is encoded by the SCAP gene. SCAP is an enzyme that plays a crucial role in the regulation of lipid metabolism.

Function

SCAP is an essential component of the sterol regulatory element-binding protein (SREBP) pathway, which regulates the synthesis of cholesterol and fatty acids in the liver. SCAP binds to SREBPs and escorts them from the endoplasmic reticulum (ER) to the Golgi apparatus, where the SREBPs are cleaved by site-1 protease (S1P) and site-2 protease (S2P). This cleavage releases the transcriptionally active N-terminal domain of the SREBPs, which then enters the nucleus and activates the transcription of genes involved in lipid synthesis and uptake.

Structure

SCAP is a polytopic transmembrane protein that contains a sterol-sensing domain (SSD). The SSD is responsible for sensing changes in cellular sterol levels and regulating the movement of SCAP and SREBP from the ER to the Golgi. When sterol levels are high, SCAP binds to insulin-induced gene (INSIG) proteins in the ER, preventing the transport of SCAP and SREBP to the Golgi and thereby inhibiting lipid synthesis.

Clinical significance

Mutations in the SCAP gene can lead to dysregulation of lipid metabolism, contributing to conditions such as familial hypercholesterolemia and metabolic syndrome. In addition, overexpression of SCAP has been associated with the progression of certain types of cancer, including hepatocellular carcinoma and prostate cancer.

File:SCAP protein structure.jpg

Structure of the SCAP protein. The SSD is shown in red.

See also

• Sterol regulatory element-binding protein
• Lipid metabolism
• Cholesterol
• Fatty acid