title: HIV-1 p6 - a structured to flexible multifunctional membrane-interacting protein.
abstract: The human immunodeficiency virus type 1 (HIV-1) p6 protein has recently been recognized as a docking site for several cellular and viral binding partners and is important for the formation of infectious viruses. Most of its known functions are suggested to occur under hydrophobic conditions near the cytoplasmic membrane, where the protein is presumed to exist in its most structured state. Although p6 is involved in manifold specific interactions, the protein has previously been considered to possess a random structure in aqueous solution. We show that p6 exhibits a defined structure with N- and C-terminal helical domains, connected by a flexible hinge region in 100mM dodecylphosphocholine micelle solution at pH 7 devoid of any organic co-solvents, indicating that this is a genuine limiting structural feature of the molecule in a hydrophobic environment. Furthermore, we show that p6 directly interacts with a cytoplasmic model membrane through both N-terminal and C-terminal regions by use of surface plasmon resonance (SPR) spectroscopy. Phosphorylation of Ser-40 located in the center of the C-terminal α-helix does not alter the secondary structure of the protein but amplifies the interaction with membranes significantly, indicating that p6 binds to the polar head groups at the surface of the cytoplasmic membrane. The increased hydrophobic membrane interaction of p6(23-52) S40F correlated with the observed increased amount of the polyprotein Gag in the RIPA insoluble fraction when Ser40 of p6 was mutated with Phe indicating that p6 modulates the membrane interactions of HIV-1 Gag.
authors.affiliation: Department of Chemistry and Centre for Pharmacy, University of Bergen, N-5007 Bergen, Norway.
authors.forename: Sara Marie Øie
authors.initials: SM
authors.lastname: Solbak
authors.forename: Tove Ragna
authors.initials: TR
authors.lastname: Reksten
authors.forename: Friedrich
authors.initials: F
authors.lastname: Hahn
authors.forename: Victor
authors.initials: V
authors.lastname: Wray
authors.forename: Petra
authors.initials: P
authors.lastname: Henklein
authors.forename: Peter
authors.initials: P
authors.lastname: Henklein
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Halskau
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schubert
authors.forename: Torgils
authors.initials: T
authors.lastname: Fossen
mesh_terms: D000818:Animals; D001703:Biophysics / Q000379:methods; D002308:Cardiolipins / Q000737:chemistry; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D013058:Mass Spectrometry / Q000379:methods; D008823:Micelles; D010455:Peptides / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012694:Serine / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013109:Sphingomyelins / Q000737:chemistry; D020349:Surface Plasmon Resonance; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry*
chemical_list: D002308:Cardiolipins; D008081:Liposomes; D008823:Micelles; D010455:Peptides; D010713:Phosphatidylcholines; D012997:Solvents; D013109:Sphingomyelins; D054301:gag Gene Products, Human Immunodeficiency Virus; C083002:p6 gag protein, Human immunodeficiency virus 1; D012694:Serine