title: Crystal structure of the human supernatant protein factor.
abstract: Supernatant protein factor (SPF) promotes the epoxidation of squalene catalyzed by microsomes. Several studies suggest its in vivo role in the cholesterol biosynthetic pathway by a yet unknown mechanism. SPF belongs to a family of lipid binding proteins called CRAL_TRIO, which include yeast phosphatidylinositol transfer protein Sec14 and tocopherol transfer protein TTP. The crystal structure of human SPF at a resolution of 1.9 A reveals a two domain topology. The N-terminal 275 residues form a Sec14-like domain, while the C-terminal 115 residues consist of an eight-stranded jelly-roll barrel similar to that found in many viral protein structures. The ligand binding cavity has a peculiar horseshoe-like shape. Contrary to the Sec14 crystal structure, the lipid-exchange loop is in a closed conformation, suggesting a mechanism for lipid exchange.
authors.affiliation: Department of Chemistry and Biochemistry, University of Berne, Freiestrasse 3, Bern, Switzerland. achim.stocker@ibc.unibe.ch
authors.forename: Achim
authors.initials: A
authors.lastname: Stocker
authors.forename: Takashi
authors.initials: T
authors.lastname: Tomizaki
authors.forename: Clemens
authors.initials: C
authors.lastname: Schulze-Briese
authors.forename: Ulrich
authors.initials: U
authors.lastname: Baumann
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006801:Humans; D008024:Ligands; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000737:chemistry*; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D021241:Spectrometry, Mass, Electrospray Ionization; D015534:Trans-Activators
chemical_list: D002352:Carrier Proteins; D008024:Ligands; D008074:Lipoproteins; C432422:SEC14L2 protein, human; D015534:Trans-Activators