|Title||Membrane Binding of HIV-1 MA Protein: Dependence on Bilayer Composition and Protein Lipidation.|
|Publication Type||Journal Article|
|Year of Publication||2016|
|Authors||Barros, M, Heinrich, F, Datta, SAK, Rein, A, Karageorgos, I, Nanda, H, Lösche, M|
|Date Published||2016 Feb 24|
By assembling in a protein lattice on the host's plasma membrane, the retroviral Gag polyprotein triggers formation of the viral protein/membrane shell. The MA domain of Gag employs multiple signals - electrostatic, hydrophobic and lipid-specific - to bring the protein to the plasma membrane, thereby complementing protein-protein interactions, located in full-length Gag, in lattice formation. We report the interaction of myristoylated and unmyristoylated HIV-1 Gag MA domains with bilayers composed of purified lipid components to dissect these complex membrane signals and quantify their contributions to the overall interaction. SPR on well-defined planar membrane models is used to quantify binding affinities and amounts of protein and yields free binding energy contributions, ΔG, of the various signals. Charge-charge interactions in the absence of the phosphatidylinositide PI(4,5)P2 attract the protein to acidic membrane surfaces, and myristoylation increases the affinity by a factor of 10; thus our data does not provide evidence for a PI(4,5)P2-trigger of myristate exposure. Lipid-specific interactions with PI(4,5)P2, the major signal lipid in the inner plasma membrane, increase membrane attraction at a similar level as the protein lipidation. While cholesterol does not directly engage in interactions, it augments protein affinity strongly by facilitating efficient myristate insertion and PI(4,5)P2 binding. We thus observe that the isolated MA protein, in the absence of protein-protein interaction conferred by the full-length Gag, binds the membrane with sub-micromolar affinities.
IMPORTANCE: Just as other retroviral species, the Gag polyprotein of HIV-1 contains three major domains: The N-terminal, myristoylated MA domain that targets the protein to the plasma membrane of the host; a central capsid-forming domain; and the C-terminal, genome-binding nucleocapsid domain. These domains act in concert to condense Gag into a membrane-bounded protein lattice that recruits genomic RNA into the virus and forms the shell of a budding immature viral capsid. In binding studies of HIV-1 Gag MA to model membranes with well-controlled lipid composition, we dissect the multiple interactions of the MA domain with its target membrane. This results in a detailed understanding of the thermodynamic aspects that determine membrane association, preferential lipid recruitment to the viral shell, and those aspects of Gag assembly into the membrane-bound protein lattice that are determined by MA.
|Alternate Journal||J. Virol.|