Cholesterol-binding START domain of mammalian STARD3 and related proteins
This subgroup includes the steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domains of STARD3 (also known as metastatic lymph node 64/MLN64) and related proteins. 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. STARD3 has a high affinity for cholesterol. It may function in trafficking endosomal cholesterol to a cytosolic acceptor or membrane. In addition to having a cytoplasmic START cholesterol-binding domain, STARD3 also contains an N-terminal MENTAL cholesterol-binding and protein-protein interaction domain. The MENTAL domain contains transmembrane helices and anchors MLN64 to endosome membranes. The gene encoding STARD3 is overexpressed in about 25% of breast cancers.