title: A retained secretory signal peptide mediates high density lipoprotein (HDL) assembly and function of haptoglobin-related protein.
abstract: Haptoglobin-related protein (Hpr) is a component of a minor subspecies of high density lipoproteins (HDL) that function in innate immunity. Here we show that assembly of Hpr into HDL is mediated by its retained N-terminal signal peptide, an unusual feature for a secreted protein and the major difference between Hpr and the soluble acute phase protein haptoglobin (Hp). The 18-amino acid signal peptide is necessary for binding to HDL and interacts directly with the hydrocarbon region of lipids. Utilizing model liposomes, we show that the rate of assembly and steady-state distribution of Hpr in lipid particles is mediated by the physical property of lipid fluidity. Dye release assays reveal that Hpr interacts more rapidly with fluid liposomes. Conversely, steady-state binding assays indicate that more rigid lipid compositions stabilize Hpr association. Lipid association also plays a role in facilitating hemoglobin binding by Hpr. Our data may offer an explanation for the distinct distribution of Hpr among HDL subspecies. Rather than protein-protein interactions mediating localization, direct interaction with phospholipids and sensitivity to lipid fluidity may be sufficient for localization of Hpr and may represent a mechanism of HDL subspeciation.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: John M
authors.initials: JM
authors.lastname: Harrington
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: Tuiumkan
authors.initials: T
authors.lastname: Nishanova
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: Savannah Rose
authors.initials: SR
authors.lastname: Pena
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: Matthew
authors.initials: M
authors.lastname: Hess
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: Chris L
authors.initials: CL
authors.lastname: Scelsi
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: Justin
authors.initials: J
authors.lastname: Widener
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602 shajduk@bmb.uga.edu.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Hajduk
mesh_terms: D000595:Amino Acid Sequence; D016880:Anisotropy; D000951:Antigens, Neoplasm / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001053:Apolipoproteins / Q000737:chemistry / Q000378:metabolism; D015153:Blotting, Western; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D057809:HEK293 Cells; D006242:Haptoglobins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006454:Hemoglobins / Q000737:chemistry / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D008075:Lipoproteins, HDL / Q000737:chemistry / Q000378:metabolism*; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008560:Membrane Fluidity; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D021382:Protein Sorting Signals; D017386:Sequence Homology, Amino Acid
chemical_list: D000951:Antigens, Neoplasm; D001053:Apolipoproteins; C058632:HPR protein, human; D006242:Haptoglobins; D006454:Hemoglobins; D008075:Lipoproteins, HDL; D008081:Liposomes; D010743:Phospholipids; D021382:Protein Sorting Signals
keywords: Apolipoprotein; High Density Lipoprotein (HDL); Lipid Fluidity; Lipoprotein Metabolism; Liposome; Phospholipid; Signal Peptide; Trypanosome Lytic Factor