The Lipid Transporter Proteins ORP5 and ORP8 in Ca2+signaling

Oxysterol-binding protein (OSBP)-related proteins (ORPs), a family of lipid transfer proteins (LTPs), mediate the exchange of the lipids PI(4)P and phosphatidylserine (PtdSer) between the plasma membrane (PM) and the endoplasmic reticulum (ER). ORP5 and ORP8 are located and function at membrane contact sites (MCSs), including the ER/PM junctions. MCSs between the ER and PM are essential platform for Ca2+ signaling complexes and within them the ER Ca2+ sensor STIM1 and the PM Ca2+ influx channel Orai1.