9.B.39.1.3
Scavenger receptor class B, member 1 (SR-B1; SCARB1; CD36L1; CLA1) of 552 aas and 2 very hydrophobic TMSs, one at the N-terminus and one near the C-terminus, possibly with as many as 3 other less hydrophobic TMSs. It comprises the hepatits C receptor together with its co-receptor, CD81 tetraspanin (Bartosch et al., 2003). When defective, it leads to antibody deficiency. SR-B1 is a receptor for different ligands such as phospholipids, cholesterol esters, lipoproteins, phosphatidylserine and apoptotic cells (Proudfoot and Sahoo 2019). It facilitates the flux of free and esterified cholesterol between the cell surface and extracellular donors and acceptors, such as high density lipoproteins (HDL) and to a lesser extent, apoB-containing lipoproteins and modified lipoproteins (Orlowski et al. 2007). It is necessary for selective HDL-cholesterol uptake (Zanoni et al. 2016). It is probably involved in the phagocytosis of apoptotic cells, via its phosphatidylserine binding activity.  Several proteins have been implicated in fatty acid transport by enterocytes including the scavenger receptor CD36 (SR-B2), the scavenger receptor B1 (SR-B1), and the FA transport protein 4 (FATP4) (Cifarelli and Abumrad 2018). Fatty acetates are volatile compounds that bind specifically to amino acid region 149-168 of CD36 (Tsuzuki et al. 2022). SR-BI is highly expressed in liver and steroidogenic tissues (Yu 2022). It regulates selective uptake of cholesterol esters (CEs) from HDL, revealing its role in mediating reverse cholesterol transport (RCT) and steroid hormone synthesis. In addition, SR-BI is involved in cholesterol transport, cellular inflammatory responses, platelet reactivity, and HDL-initiated signaling in the vascular system in several mouse models. Mutations in the human SR-BI gene (SCARB1) have been found to be associated with abnormally high plasma HDL-C levels and an increased risk of atherosclerotic cardiovascular disease. The key regions of SR-BI transmembrane structure and the regulatory mechanisms of SR-BI expression have been reviewed (Yu 2022). A short amphipathic alpha helix in scavenger receptor BI facilitates bidirectional HDL-cholesterol transport through a hydrophobic tunnel within SR-BI (May and Sahoo 2022).  A deficiency of SR-B1 reduced the tumor load of colitis-induced or APC^{min /+} -induced colorectal cancer (Chen et al. 2023).