title: The conformation of human phospholipid scramblase 1, as studied by infrared spectroscopy. Effects of calcium and detergent.
abstract: Human phospholipid scramblase 1 (SCR) is a membrane protein that catalyzes the transmembrane (flip-flop) motion of phospholipids. It can also exist in a non membrane-bound form in the nucleus, where it modulates several aspects of gene expression. Catalysis of phospholipid flip-flop requires the presence of millimolar Ca2+, and occurs in the absence of ATP. Membrane-bound SCR contains a C-terminal α-helical domain embedded in the membrane bilayer. The latter domain can be removed giving rise to a stable truncated mutant SCRΔ that is devoid of scramblase activity. In order to improve our understanding of SCR structure infrared spectra have been recorded of both the native and truncated forms, and the effects of adding Ca2+, or removing detergent, or thermally denaturing the protein have been observed. Under all conditions the main structural component of SCR/SCRΔ is a β-sheet. Removing the C-terminal 28 aa residues, which anchor SCR to the membrane, leads to a change in tertiary structure and an increased structural flexibility. The main effect of Ca2+is an increase in the α/β ratio of secondary structure components, with a concomitant increase in the proportion of non-periodic structures. At least in SCRΔ, detergent (Zwittergent 3-12) decreases the structural flexibility, an effect somewhat opposite to that of increasing temperature. Thermal denaturation is affected by Ca2+, detergent, and by the presence or absence of the C-terminal domain, each of them influencing in different ways the denaturation pattern.
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Nagore
authors.initials: N
authors.lastname: Andraka
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Lissete
authors.initials: L
authors.lastname: Sánchez-Magraner
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Marcos
authors.initials: M
authors.lastname: García-Pacios
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.forename: Félix M
authors.initials: FM
authors.lastname: Goñi
authors.affiliation: Unidad de Biofísica (CSIC, UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, P.O. Box 644, 48080 Bilbao, Spain. Electronic address: joseluis.arrondo@ehu.es.
authors.forename: José L R
authors.initials: JL
authors.lastname: Arrondo
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D003902:Detergents / Q000494:pharmacology*; D006801:Humans; D049294:Phospholipid Transfer Proteins / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: D003902:Detergents; C493422:PLSCR1 protein, human; D049294:Phospholipid Transfer Proteins; D002118:Calcium
keywords: 2D IR correlation spectroscopy; Calcium; Detergents; Infrared spectroscopy; Membranes; Protein structure; Scramblase