Lipid-binding START domain of mammalian STARD2, -7, and related proteins
This subfamily includes the steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domains of STARD2 (also known as phosphatidylcholine transfer protein/PC-TP), and STARD7 (also known as gestational trophoblastic tumor 1/GTT1). The START domain family belongs to the SRPBCC (START/RHO_alpha_C/PITP/Bet_v1/CoxG/CalC) domain superfamily of proteins that bind hydrophobic ligands. SRPBCC domains have a deep hydrophobic ligand-binding pocket. STARD2 is a cytosolic phosphatidycholine (PtdCho) transfer protein, which traffics PtdCho, the most common class of phospholipids in eukaryotes, between membranes. It represents a minimal START domain structure. STARD2 plays roles in hepatic cholesterol metabolism, in the development of atherosclerosis, and may also have a mitochondrial function. The gene encoding STARD7 is overexpressed in choriocarcinoma. STARD7 appears to be involved in the intracellular trafficking of PtdCho to mitochondria. STARD7 was shown to be surface active and to interact differentially with phospholipid monolayers. It showed a preference for phosphatidylserine, cholesterol, and phosphatidylglycerol.