The C-terminal transmembrane domain of human phospholipid scramblase 1 is essential for the protein flip-flop activity and Ca2+-binding

• Published in: The Journal of membrane biology 2014-02, Vol.247 (2), p.155-165
• Main Authors: Sánchez-Magraner, Lissete, Posada, Itziar M. D., Andraka, Nagore, Contreras, F. Xabier, Viguera, Ana R., Guérin, Diego M. A., Arrondo, José L. R., Monaco, Hugo L., Goñi, Félix M.
• Format: Article
• Language: English
• Subjects: Biochemistry; Biomedical and Life Sciences; Calcium - metabolism; Enzyme Activation; Human Physiology; Humans; Life Sciences; Lipid Metabolism; Mutation; Phospholipid Transfer Proteins - chemistry; Phospholipid Transfer Proteins - genetics; Phospholipid Transfer Proteins - metabolism; Protein Binding; Protein Interaction Domains and Motifs - physiology; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Thermodynamics
• ISSN: 0022-2631; 1432-1424
• DOI: 10.1007/s00232-013-9619-7

Human phospholipid scramblase 1 (SCR) is a 318 amino acid protein that was originally described as catalyzing phospholipid transbilayer (flip-flop) motion in plasma membranes in a Ca 2+ -dependent, ATP-independent way. Further studies have suggested an intranuclear role for this protein in addition. A putative transmembrane domain located at the C terminus (aa 291–309) has been related to the flip-flop catalysis. In order to clarify the role of the C-terminal region of SCR, a mutant was produced (SCRΔ) in which the last 28 amino acid residues were lacking, including the α-helix. SCRΔ had lost the scramblase activity and its affinity for Ca 2+ was decreased by one order of magnitude. Fluorescence and IR spectroscopic studies revealed that the C-terminal region of SCR was essential for the proper folding of the protein. Moreover, it was found that Ca 2+ exerted an overall destabilizing effect on SCR, which might facilitate its binding to membranes.