SREBP-1, Mouse anti-Hamster, Canine, Human, Clone: 2A4, Millipore Sigma™

Sterol regulatory element-binding protein 1 (UniProt: P36956; also known as SREBP-1, Class D basic helix-loop-helix protein 1, bHLHd1, Sterol regulatory element-binding transcription factor 1) is encoded by the SREBF1 (also known as BHLHD1, SREBP1) gene (Gene ID: 6720) in human. SREBP-1 is a multi-pass membrane protein found on nuclear, endoplasmic reticulum, and Golgi membranes. It attaches to membranes via two hydrophobic sequences (aa 477-497 and 536-556). It is expressed in a wide variety of tissues, but is most abundant in liver and adrenal gland. Six isoforms of SREBP-1 have been described that are produced by alternative splicing. Isoform SREBP-1C predominates in liver, adrenal gland, and ovary, whereas isoform SREBP-1A predominates in hepatoma cell lines. Both isoforms are found in kidney, brain, white fat, and muscle. It serves as a transcriptional activator that is essential for lipid homeostasis and regulates transcription of the LDL receptor gene. It is also involved in fatty acid and cholesterol synthesis. It acts by binds to the sterol regulatory element 1 (SRE-1) (5'-ATCACCCCAC-3') and displays dual sequence specificity binding to both an E-box motif (5'-ATCACGTGA-3') and to SRE-1 (5'-ATCACCCCAC-3'). SREBP-1 has two cytoplasmic domains (aa 1-487 and 569-1147), two transmembrane domains (aa 88-508 and 548-568), and one lumenal domain (aa 509-547). In the precursor form, which has a hairpin orientation in the membrane both the N-terminal transcription factor domain and the C-terminal regulatory domain face the cytoplasm. Two separate site-specific proteolytic cleavages are required for release of the transcriptionally active N-terminal domain. These cleavages are carried out by two distinct proteases, called site-1 protease (S1P; aa 490-491) and site-2 protease (S2P; aa 530-531). SREBP-1 can be phosphorylated by AMPK at Ser402, which suppress its processing and nuclear translocation, and thereby repress target gene expression.