Lipid-binding START domain of mammalian STARD4 and related proteins
This subgroup includes the steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domains of mammalian STARD4 and related domains. It belongs to the START domain family, and in turn 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. STARD4 plays an important role in steroidogenesis, trafficking cholesterol into mitochondria. It specifically binds cholesterol, and demonstrates limited binding to another sterol, 7alpha-hydroxycholesterol. STARD4 is ubiquitously expressed, with highest levels in liver and kidney.