Lipid-binding SRPBCC domain of mammalian PITPNC1,and related proteins (Class IIB PITPs)
This subgroup includes the N-terminal SRPBCC (START/RHO_alpha_C /PITP /Bet_v1/CoxG/CalC) domain of mammalian Class IIB phosphatidylinositol transfer protein (PITP), PITPNC1/RdgBbeta, and related proteins. These are metazoan proteins belonging to the PITP family of lipid transfer proteins, and to the SRPBCC domain superfamily of proteins that bind hydrophobic ligands. SRPBCC domains have a deep hydrophobic ligand-binding pocket. In vitro, PITPs bind phosphatidylinositol (PtdIns), as well as phosphatidylcholine (PtdCho) but with a lower affinity. They transfer these lipids from one membrane compartment to another. The cellular roles of PITPs include inositol lipid signaling, PtdIns metabolism, and membrane trafficking. Mammalian PITPNC1 contains an amino-terminal SRPBCC PITP-like domain and a short carboxyl-terminal domain. It is a cytoplasmic protein, and is ubiquitously expressed. It can transfer phosphatidylinositol (PtdIns) in vitro with a similar ability to other PITPs.