title: Structural and Molecular Determinants of Membrane Binding by the HIV-1 Matrix Protein.
abstract: Assembly of HIV-1 particles is initiated by the trafficking of viral Gag polyproteins from the cytoplasm to the plasma membrane, where they co-localize and bud to form immature particles. Membrane targeting is mediated by the N-terminally myristoylated matrix (MA) domain of Gag and is dependent on the plasma membrane marker phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2]. Recent studies revealed that PI(4,5)P2 molecules containing truncated acyl chains [tr-PI(4,5)P2] are capable of binding MA in an "extended lipid" conformation and promoting myristoyl exposure. Here we report that tr-PI(4,5)P2 molecules also readily bind to non-membrane proteins, including HIV-1 capsid, which prompted us to re-examine MA-PI(4,5)P2 interactions using native lipids and membrane mimetic liposomes and bicelles. Liposome binding trends observed using a recently developed NMR approach paralleled results of flotation assays, although the affinities measured under the equilibrium conditions of NMR experiments were significantly higher. Native PI(4,5)P2 enhanced MA binding to liposomes designed to mimic non-raft-like regions of the membrane, suggesting the possibility that binding of the protein to disordered domains may precede Gag association with, or nucleation of, rafts. Studies with bicelles revealed a subset of surface and myr-associated MA residues that are sensitive to native PI(4,5)P2, but cleft residues that interact with the 2'-acyl chains of tr-PI(4,5)P2 molecules in aqueous solution were insensitive to native PI(4,5)P2 in bicelles. Our findings call to question extended-lipid MA:membrane binding models, and instead support a model put forward from coarse-grained simulations indicating that binding is mediated predominantly by dynamic, electrostatic interactions between conserved basic residues of MA and multiple PI(4,5)P2 and phosphatidylserine molecules.
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
authors.forename: Peter Y
authors.initials: PY
authors.lastname: Mercredi
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
authors.forename: Nadine
authors.initials: N
authors.lastname: Bucca
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
authors.forename: Burk
authors.initials: B
authors.lastname: Loeliger
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
authors.forename: Christy R
authors.initials: CR
authors.lastname: Gaines
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
authors.forename: Mansi
authors.initials: M
authors.lastname: Mehta
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
authors.forename: Pallavi
authors.initials: P
authors.lastname: Bhargava
authors.affiliation: Virus-Cell Interaction Section, HIV Dynamics and Replication Program, National Cancer Institute at Fredrick, Fredrick, MD 21702-1201, USA.
authors.forename: Philip R
authors.initials: PR
authors.lastname: Tedbury
authors.affiliation: Institut des Biomolécules Max Mousseron, CNRS UMR5247, Université Montpellier, Faculté de Pharmacie, Montpellier Cedex 05, France.
authors.forename: Landry
authors.initials: L
authors.lastname: Charlier
authors.affiliation: Institut des Biomolécules Max Mousseron, CNRS UMR5247, Université Montpellier, Faculté de Pharmacie, Montpellier Cedex 05, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Floquet
authors.affiliation: Centre d'études d'agents Pathogénes et Biotechnologies pour la Santé CNRS-UMR 5236, Université Montpellier, Montpellier Cedex 5, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Muriaux
authors.affiliation: Centre d'études d'agents Pathogénes et Biotechnologies pour la Santé CNRS-UMR 5236, Université Montpellier, Montpellier Cedex 5, France.
authors.forename: Cyril
authors.initials: C
authors.lastname: Favard
authors.affiliation: Department of Biochemistry, Center for Structural Biology, and Institute of Chemical Biology, Vanderbilt University School of Medicine, Nashville, TN 37240-7917, USA.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Sanders
authors.affiliation: Virus-Cell Interaction Section, HIV Dynamics and Replication Program, National Cancer Institute at Fredrick, Fredrick, MD 21702-1201, USA. Electronic address: efreed@mail.nih.gov.
authors.forename: Eric O
authors.initials: EO
authors.lastname: Freed
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA. Electronic address: janm@umbc.edu.
authors.forename: Jan
authors.initials: J
authors.lastname: Marchant
authors.affiliation: Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA. Electronic address: summers@hhmi.umbc.edu.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Summers
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D015497:HIV-1 / Q000502:physiology*; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D021962:Membrane Microdomains; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010718:Phosphatidylserines / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008055:Lipids; D008081:Liposomes; D019269:Phosphatidylinositol 4,5-Diphosphate; D010718:Phosphatidylserines; D054301:gag Gene Products, Human Immunodeficiency Virus
keywords: HIV-1 matrix protein; PIP2; bicelles; membrane targeting; polysomes