Lipid-binding START domain of mammalian STARD1-STARD15 and related proteins
This family includes the steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domains of mammalian STARD1-STARD15, and related domains, such as the START domain of the Arabidopsis homeobox protein GLABRA 2. The mammalian STARDs are grouped into 8 subfamilies. This 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. For some members of this family, specific lipids that bind in this pocket are known; these include cholesterol (STARD1/STARD3/ STARD4/STARD5), 25-hydroxycholesterol (STARD5), phosphatidylcholine (STARD2/ STARD7/STARD10), phosphatidylethanolamine (STARD10) and ceramides (STARD11). The START domain is found either alone or in association with other domains. Mammalian STARDs participate in the control of various cellular processes including lipid trafficking between intracellular compartments, lipid metabolism, and modulation of signaling events. Mutation or altered expression of STARDs is linked to diseases such as cancer, genetic disorders, and autoimmune disease. The Arabidopsis homeobox protein GLABRA 2 suppresses root hair formation in hairless epidermal root cells.