title: Membrane binding of human phospholipid scramblase 1 cytoplasmic domain.
abstract: Human phospholipid scramblase 1 (SCR) consists of a large cytoplasmic domain and a small presumed transmembrane domain near the C-terminal end of the protein. Previous studies with the SCRΔ mutant lacking the C-terminal portion (last 28 aa) revealed the importance of this C-terminal moiety for protein function and calcium-binding affinity. The present contribution is intended to elucidate the effect of the transmembrane domain suppression on SCRΔ binding to model membranes (lipid monolayers and bilayers) and on SCRΔ reconstitution in proteoliposomes. In all cases the protein cytoplasmic domain showed a great affinity for lipid membranes, and behaved in most aspects as an intrinsic membrane protein. Assays have been performed in the presence of phosphatidylserine, presumably important for the SCR cytoplasmic domain to be electrostatically anchored to the plasma membrane inner surface. The fusion protein maltose binding protein-SCR has also been studied as an intermediate case of a molecule that can insert into the bilayer hydrophobic core, yet it is stable in detergent-free buffers. Although the intracellular location of SCR has been the object of debate, the present data support the view of SCR as an integral membrane protein, in which not only the transmembrane domain but also the cytoplasmic moiety play a role in membrane docking of the protein.
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU), Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Itziar M D
authors.initials: IM
authors.lastname: Posada
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU), Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain; Department of Biotechnology, Università degli studi di Verona, 37134, Verona, Italy.
authors.forename: Lissete
authors.initials: L
authors.lastname: Sánchez-Magraner
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU), Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Javier H
authors.initials: JH
authors.lastname: Hervás
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU), Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Alicia
authors.initials: A
authors.lastname: Alonso
authors.affiliation: Department of Biotechnology, Università degli studi di Verona, 37134, Verona, Italy.
authors.forename: Hugo L
authors.initials: HL
authors.lastname: Monaco
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU), Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain. Electronic address: felix.goni@ehu.es.
authors.forename: Félix M
authors.initials: FM
authors.lastname: Goñi
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D049294:Phospholipid Transfer Proteins / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011510:Proteolipids / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D008563:Membrane Lipids; C493422:PLSCR1 protein, human; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D011510:Proteolipids; C020485:proteoliposomes; D014867:Water
keywords: Cytoplasmic domain; Membrane protein reconstitution; Phospholipid scramblase 1; Protein insertion into membranes; Transmembrane domain; Triton X-114