Meta-Biol

• Pathways

Oxysterol-binding proteins (OSBPs) and OSBP-related proteins (ORPs) comprise a 12-member mammalian gene family of intracellular lipid receptors which bind oxygenated cholesterol derivatives and are thought to mediate sterol and phospholipid synthesis (Olkkonen & Li 2013, Weber-Boyvat et al. 2013). A conserved OSBP homology domain (OHD) binds sterols and lipids and a pleckstrin homology (PH) domain and two phenylalanines in an acidic tract (FFAT) motif mediate interaction with organelle membranes (Olkkonen 2015). The primary function of the protein family remains unresolved. Most (OSBPL2,3,6,7,9 and 1A), if not all of the OSBPLs are thought to bind and coordinate distribution of oxygenated cholesterol derivatives such as 25-hydroxycholesterol (25OH-CHOL). Oxysterol-binding protein 2 (OSBP2, aka ORP4) is primarily expressed in brain, and to a lesser extent in heart, skeletal muscle, spleen and kidney. It has a diffuse cytoplasmic localisation profile and is a high-affinity 25OH-CHOL binding protein (Wang et al. 2002, Suchanek et al. 2007). RNAi silencing of all OSBP2 variants in HEK293 and HeLa cells resulted in growth arrest but not cell death, suggesting OSBP2 is essential for cell proliferation and survival (Charman et al. 2014).